Physics GCSE

Physics GCSE glossary

1837 key terms for Physics GCSE, A to Z, each linked to the topic pages that use it.

Find a term in Physics GCSE

1837 terms found. Open a term to try a short memory check.

A

a = F ÷ m: Rearranged, a = F ÷ m, so the same force produces greater acceleration on a smaller mass.AQA
a = Δv ÷ t: Acceleration is the rate of change of velocity, found by dividing the change in velocity by the time taken.AQA
absorbers: Paper or skin stops alpha, a few millimetres of aluminium stops beta, and thick lead or concrete reduces gamma.AQA
Absorbing materials: Paper or a few centimetres of air stop alpha particles, a few millimetres of aluminium stop beta particles, and thick lead or concrete reduce gamma rays.OCR
absorption: Some electromagnetic waves are taken in by materials, such as microwaves being absorbed by water molecules to heat food or X-rays being absorbed by bone.AQA, OCR
absorption and emission: Absorbing electromagnetic radiation moves an electron further from the nucleus to a higher energy level, while emitting it moves the electron closer to the…AQA
Absorption and emission of radiation: A body's temperature rises when it absorbs more radiation than it emits, falls when it emits more than it absorbs, and stays constant when the rates are equal.OCR
absorption by an aerial: The radio wave is absorbed by the aerial, and the oscillating electric field it carries pushes the free electrons in the metal backwards and forwards.AQA
absorption by the Earth: The rate at which radiation is absorbed by the surface and the atmosphere is one factor the Earth's temperature depends on.AQA
absorption contrast: Materials soak up some waves more than others, so a structure such as dense bone or a flaw in a casting shows up as a shadow against another.AQA
absorption line spectra: Dark lines in a galaxy's spectrum, produced by known elements and appearing at known wavelengths in the laboratory, used to measure the size of the shift.AQA
accelerating expansion: The conclusion that the expansion of the universe is not slowing but accelerating, so distant galaxies are receding ever faster.AQA
Acceleration: The rate of change of speed, found by dividing the change in speed between two points by the time taken between them when speed increases.AQA, OCR
Acceleration and units: The acceleration due to gravity is represented by g, is approximately 9.8 m/s² and may be approximated to 10 m/s² in calculations.AQA
acceleration as a curve: When the object is accelerating, the line curves upwards with an increasing gradient.AQA
Acceleration as rate of change of velocity: Judged by dividing the change in velocity by the time taken, using acceleration = change in velocity ÷ time.OCR
Acceleration due to gravity: About 9.8 m/s², commonly rounded to 10 m/s² in calculations, acting as a magnitude with direction downward.OCR
Acceleration equation: The equation a = Δv ÷ t, in which the value of Δv is used correctly.AQA
accepting a model: A suggestion becomes an accepted model only when its predictions are tested against measurement.AQA
Accuracy: Reading at eye level, choosing a scale that suits the size of the quantity, and recording with a sensible number of significant figures and correct units.OCR
Accurate reading of scales: Reading scales at eye level to avoid parallax error and noting the smallest division to judge precision.OCR
Accurate recording with units: Always stating the unit with a measurement, such as cm, g, s, cm³ or °C.OCR
across versus through: Potential difference is always across a component, while current is always through a component because it passes along the path.AQA
acting on different objects: The two forces of an interaction pair each act on a different object, which is why they never cancel each other out on any single object.AQA
activity: The rate at which a source of unstable nuclei decays, measured in becquerels (Bq), where 1 Bq equals one decay per second.AQA
activity against duration: A short half-life gives a high activity and a large dose over a short time, while a long half-life gives a lower activity but a hazard lasting a very long time.AQA
activity and half-life: A short half-life means each nucleus is very likely to decay soon, so for the same number of nuclei the activity is high.AQA
adding and subtracting forces: The simple method of finding the resultant of two forces on the same straight line once a positive direction is fixed.AQA
adding fields of turns: Each turn carries the same current the same way round, so where the turns sit side by side their fields point the same way inside the coil and add together.AQA
adding scalars: Scalars of the same kind add as ordinary numbers, so walking 3 km then 4 km always totals 7 km of distance however the route bends.AQA
adverse conditions: Road and weather conditions that can affect the braking distance of a vehicle.AQA
aerial: The part of the circuit in which an alternating current makes charges oscillate and from which the radio wave travels away.AQA
ageing: It stiffens and damages hair cells and the cochlea, so the upper limit falls, high frequencies are lost first, and the audible range narrows.OCR
agreement with observations: When a model's predictions are tested against measurement and the two agree, which is why the scientific community adopted Bohr's version of the atom.AQA
air and water resistance: The friction of a fluid on an object moving through it, growing larger as the object speeds up.AQA
air resistance: A resistive force that grows as the vehicle goes faster, because the car sweeps through more air every second.AQA
Air resistance and resultant force: If air resistance becomes significant, the resultant downward force decreases and acceleration is less than 9.8 m/s².AQA
alcohol and drugs: Factors that can affect a driver's reaction time; data shows the mean reaction time rises after drinking but not by the same amount for everyone.AQA
alignment with a field: The needle lines up with the direction of the magnetic field it is in rather than being pulled by it.AQA
All bodies emit radiation: Every object with a temperature above absolute zero emits electromagnetic radiation.OCR
alpha decay: A type of decay that causes both the mass and charge of the nucleus to decrease.AQA
Alpha emission: Emitting a helium nucleus of 2 protons and 2 neutrons lowers the mass number by 4 and the proton number by 2, reducing both mass and positive charge.OCR
alpha inside the body: Inside the body alpha radiation is absorbed by tissue and organs and, being highly ionising, does a great deal of damage in a small volume.AQA
alpha particle: Consists of two neutrons and two protons, and is the same as a helium nucleus.AQA
alpha particle scattering: Firing alpha particles, which are positively charged and relatively heavy, at a very thin gold foil and recording where they went.AQA
Alpha, beta, neutron and gamma emission: An unstable nucleus can lose energy by emitting an alpha particle, a beta particle, a neutron, or gamma rays.OCR
alternating current: A supply in which the potential difference repeatedly reverses, so charges in the wire move backwards and forwards rather than drifting one way.AQA
Alternating Current (AC): An electric current that repeatedly reverses its direction of flow.AQA
Alternating current in the home: The domestic supply in the UK is a.c., so its voltage repeatedly reverses direction, swinging positive and negative many times each second.OCR
alternating potential difference: Reverses regularly, with the terminals swapping over 100 times a second, so the charge oscillates back and forth with no net drift.AQA
Alternating voltage: Repeatedly reverses polarity, so the potential difference swings between positive and negative values and the current changes direction each cycle.OCR
alternator: A machine that uses the generator effect to generate ac, spinning a coil in a magnetic field with two slip rings, one joined to each end of the coil.AQA
alternator against dynamo: The alternator trace crosses the time axis with one positive and one negative peak per revolution, while the dynamo trace stays on one side of the axis and…AQA
altitude: The height of a surface above ground level; as it increases, the column of air above the surface becomes shorter and contains fewer air molecules.AQA
altitude and cosmic rays: At high altitude there is less atmosphere above you to absorb cosmic rays, and aircrew spend working hours at altitude.AQA
always attraction: The force between a magnet and a magnetic material is always one of attraction, whichever way round the magnet is held.AQA
always virtual: The image produced by a concave lens is always virtual, because the rays spread rather than converge and can never cross beyond the lens.AQA
Ammeter: Goes in series with the component so the same current flows through it.OCR
ammeter in series: The ammeter is connected in series so the current it reads is the current through the component.AQA
ammeter placement: An ammeter always goes in series with the component whose current it measures, because the current has to pass through it.AQA
amplitude: The maximum displacement of a point from its undisturbed position, measured in metres.AQA, OCR
amplitude and frequency: The frequency of the sound matches the frequency of the current, and the amplitude of the movement sets the loudness.AQA
Apply: Substituting values correctly into either equation, including converting a percentage to a decimal or the reverse.AQA
Applying and rearranging equations: Substituting the given values correctly, keeping units consistent, and isolating the required quantity before substituting when finding flux density, current…OCR
Applying the transformer equation: List the three known quantities, rearrange for the unknown, substitute values with consistent units and calculate.OCR
Appropriate apparatus selection: Selecting a ruler with a suitable resolution, a spring that does not permanently deform, and masses that give a measurable but safe range of forces.OCR
Area: The size of a surface, measured in square metres (m²), not metres or cubic metres.AQA, OCR
Area as displacement: The enclosed area between the plotted line and the time axis represents the displacement travelled in the chosen time interval, because velocity multiplied by…OCR
Area conversion: An area given in cm² is converted to m² by multiplying by 1 × 10⁻⁴ before calculating.OCR
Area in contact: The area of the surface actually in contact with the fluid or force, not the total surface area of the object.AQA
Area of a circle: Calculated using A = πr², with the radius converted to metres before squaring.AQA
Area of a rectangle: Found by multiplying its length in metres by its width in metres.AQA
Area under a force–extension graph: Gives the work done in stretching; in linear cases the graph is a straight line from the origin, so the area is a triangle.OCR
area under a graph: The region between the line and the time axis on a velocity–time graph, from which the distance travelled can be calculated.AQA
Area under a graph as a physical quantity: The area enclosed between the plotted line and the time axis on a velocity–time graph represents the distance travelled or displacement.AQA
Area under a velocity–time graph: The region between the line and the time axis, which represents distance travelled.AQA
area under the graph: The energy can be found from the area under the force-extension line, which is a triangle.AQA
Armature: The rotating coil of wire in a DC electric motor, which carries the current and experiences the motor effect force within the magnetic field of the permanent…Pearson Edexcel
armature and contacts: The iron arm that the electromagnet attracts, and the parts the moving arm pushes together to complete the second circuit.AQA
arrangement of particles: In a solid the particles are in a regular repeating pattern, in a liquid irregularly arranged, and in a gas randomly placed.AQA
arrow conventions: Draw the arrow with a ruler, starting at the object or at the point where the quantity acts, with a single arrowhead showing the direction.AQA
arrow length shows size: Each force is drawn as a labelled arrow pointing the way the force acts, with the length showing its relative size.AQA
arrow representation: A way of showing a force on a diagram, where the length represents the size and the head shows the direction.AQA
arrowhead shows direction: The arrowhead is placed to show which way the force acts, giving the direction of the vector quantity.AQA
arrowheads in or out: Outward pointing arrowheads at both ends show a convex, converging lens, while inward pointing arrowheads show a concave, diverging lens.AQA
arrows on field lines: These represent the direction of the magnetic field, not its strength.AQA
artificial satellites: Objects launched by people that orbit the Earth or another planet, are held in orbit by gravity and are usually small, low and fast.AQA
Artificial satellites: geostationary and polar orbits: Human-made objects placed in orbit, often around Earth; a geostationary satellite orbits above the equator with a period of 24 hours, and a polar satellite…OCR
at right angles to the motion: The direction of the gravitational force on an orbiting object, so it does not speed the object up or slow it down.AQA
atmospheric pressure: Created by air molecules colliding with a surface, acting at right angles to it whichever way it faces.AQA
Atmospheric pressure and altitude: A greater height means there is less air above the point, so the atmospheric pressure is lower.OCR
Atmospheric pressure and weight of air: The weight of the air column pressing down on each unit of area, giving a pressure that acts in all directions on any surface within the air.OCR
Atomic and nuclear changes: Changes in atoms and nuclei can generate and absorb radiations over a wide frequency range.OCR
atomic number: The number of protons in an atom of an element, given the symbol Z, and written as the lower of the two numbers in the nuclide symbol.AQA
Atomic number and mass number: The subscript Z is the atomic number and the superscript A is the mass number, which counts protons plus neutrons.OCR
attraction: The pull that a gravitational field always produces between masses, never a push.OCR
attraction and repulsion: Between two like charges the field lines push apart, giving repulsion; between two opposite charges the lines run from the positive to the negative charge,…AQA, OCR
Attraction caused by induced magnetism: Induced magnetism always produces attraction towards the inducing magnet, never repulsion.OCR
attraction of neutral objects: A charged object also attracts an uncharged one, so attraction is a weaker test for charge than repulsion.AQA
audibility graphs: Graphs showing how the minimum audible level changes with age and noise exposure.AQA
audible range: Human hearing works over a limited range, roughly 20 Hz to 20 kHz in a young adult, with greatest sensitivity in the mid-frequencies.OCR
Average acceleration: Calculated by dividing the change in velocity by the time taken for that change, giving an average value over the interval.AQA
average density: The density of all the air above a surface, which falls as the surface rises because the densest air near the ground is left below.AQA
Average Kinetic Energy: The mean kinetic energy of all the particles in a gas.AQA
average speed: For the whole journey this comes from the total distance divided by the total time, the gradient of a straight line drawn from the first point to the last.AQA, OCR
average velocity: Displacement over time, which is zero for a journey returning to its start.AQA
axes and scales: Time goes on the horizontal axis and distance on the vertical, both labelled with units, using sensible scales that fill at least half the grid.AQA

B

background correction: If a background count rate is quoted anywhere in the question, subtract it from every value before you start.AQA
background radiation: Radiation included in a reading that must be measured with the source removed and subtracted before the count-rate from the source is used.AQA
Balanced and unbalanced forces: Opposing forces that are equal are balanced, while forces that are not equal leave a resultant force.OCR
balanced beam: A beam that is not turning, because the sum of every clockwise turning effect about the pivot matches the sum of every anticlockwise one.AQA
balanced forces: When the original forces are balanced the single force replacing them is zero, as for a hailstone at terminal velocity.AQA, OCR
balanced nuclear equations: Equations written using the names and symbols of common nuclei and particles, in which both the mass numbers and the atomic numbers balance.AQA
Balanced object: An object for which the total clockwise moment about the pivot equals the total anticlockwise moment.OCR
balancing equations: Limited to balancing the atomic numbers and mass numbers, with the mass numbers across the equation and the atomic numbers across the equation.AQA
Balancing mass numbers in decay equations: A nuclear equation is balanced when the mass numbers add up to the same total on both sides.OCR
balloon model: Dots inked onto a balloon all move apart as it is blown up, and the dots that start furthest apart separate fastest.AQA
basilar membrane: A structure inside the cochlea that responds strongly near its resonant range but weakly far from it.OCR
Battery as chemical store versus mains a.c. supply: A battery is a store of chemical energy, while the mains a.c.OCR
bearings: A three-figure bearing is measured clockwise from north and is one acceptable way of giving the direction.AQA
becquerel: The unit of activity, where 1 Bq is one decay per second.AQA
becquerels: The unit in which the activity of a radioactive source is measured, where 1 Bq equals one decay per second.AQA
bending towards the normal: What the ray does as it enters the glass and slows down, making the angle of refraction inside the glass smaller than the angle of incidence in the air.AQA
beta decay: A neutron inside the nucleus turns into a proton, and the electron created in the process is ejected as the beta particle.AQA
Beta emission: A fast electron created when a neutron changes into a proton leaves the mass number the same while the proton number rises by 1, increasing the positive charge.OCR
beta particle: A high speed electron ejected from the nucleus as a neutron turns into a proton.AQA
Big Bang theory: Suggests that the universe began from a very small region that was extremely hot and dense.AQA
Big-Bang model: The universe began from a very small, hot, dense region and has expanded ever since.OCR
black body: A body that does not reflect or transmit any radiation, so the whole of the incident radiation must be absorbed.AQA
blocked by liquids: S-waves travel through solid rock but stop dead at a liquid boundary, because liquids do not resist a change of shape.AQA
blue neutral: The neutral wire is identified by blue insulation covering it.AQA
blue-shift: The matching effect for an object approaching us, a shift towards shorter wavelengths, shown by a few nearby galaxies.AQA
body at 0 V: You are at earth potential whenever you stand on the ground, touch a metal pipe or lean on a damp wall.AQA
body waves: Two types travel through the body of the Earth: P-waves, which are longitudinal, and S-waves, which are transverse.AQA
Bohr model: A development of the nuclear model in which electrons orbit the nucleus at specific distances.AQA
Bohr's electron shells and energy levels: Electrons orbit the nucleus in fixed shells or energy levels, explaining why atoms emit and absorb particular energies.OCR
boundary between materials: Any place where the material a wave is travelling through changes, such as air to glass or air to a brick wall.AQA
boundary between media: The place where two different media meet, at which part of an ultrasound pulse is reflected and part is transmitted.AQA
Boyle's Law: For a fixed mass of gas at constant temperature, the pressure of the gas is inversely proportional to its volume.AQA
brake overheating: The steep rise in temperature of the brakes when energy is transferred to their thermal store at a greater rate, causing them to fade and lose their grip.AQA
brake temperature: A quantity that increases as the brakes get hot when work is done against friction between the brakes and the wheel.AQA
braking: When a vehicle slows down, the brakes do work against friction, filling the thermal store of the brakes, which is why they get hot.AQA
braking distance: The distance travelled under the braking force, during which friction does work against the motion and the vehicle decelerates.AQA, OCR
braking force: The force acting on a vehicle that produces its deceleration, with a larger value giving a larger deceleration for a given mass.AQA
Branch: A section of a parallel circuit containing one or more components, which provides a separate path for current.OCR
Branching circuits: Where a circuit branches, the current splits between the branches, so the single-loop rule applies to one loop only.OCR
brown live: The live wire is identified by brown insulation covering it.AQA
brushes: Two carbon brushes feed the current to the coil through the split-ring commutator.AQA
burglar alarms: An application that triggers when a beam falling on the LDR is broken.AQA

C

calculating gradient: Change in distance divided by change in time, which equals the speed for any straight section.AQA
Calculation of work done from force and distance: Calculating a derived value as force × distance moved along the force, and stating the unit as the joule.OCR
Calculations with powers of ten: Keeping powers of ten in standard form and handling them correctly when dividing, so the answer's unit matches the quantity requested.OCR
camera exposure: An application that uses the current directly, adjusting exposure from the light reaching an LDR.AQA
cancelling side forces: The side faces are pushed inwards equally from both directions, so those forces cancel.AQA
Carbon Brushes: Stationary electrical contacts that press against the split-ring commutator to maintain a continuous electrical connection between the external circuit and…Pearson Edexcel
Cause-and-effect explanation: The reasoning chains greater height, less air above, smaller weight, and lower pressure, rather than stating only that pressure decreases.OCR
Cell polarity conventions: The long line of a cell is the positive terminal and the short thick line is the negative terminal, so the supply pushes conventional current from positive…OCR
cells and batteries: A cell is a long thin line and a short thick line, and a battery is two or more cells in line.AQA
centre of mass: The point from which the weight may be considered to act, or where the mass appears to be concentrated.AQA
centre of the lens: The point from which the focal length is measured, rather than from the edge or the surface of the lens.AQA
Centripetal acceleration and force: An acceleration directed towards the centre of the circle, produced by a resultant force acting towards the centre.OCR
Chadwick: His experimental work provided the evidence to show the existence of neutrons within the nucleus.AQA
chain of nails: Iron nails can hang from a bar magnet, each nail becoming an induced magnet that induces magnetism in the next one down.AQA
chain reaction: A self-sustaining sequence in which at least one neutron from a fission is absorbed by another large nucleus, causing a further fission that releases more…AQA, OCR
change in height: Only the change in height counts, so a ball that rises and falls back to the start has no net change.AQA
Change in temperature: Found by subtracting the initial temperature from the final temperature, and used in the equation rather than the final temperature.OCR
Change in velocity: Found by subtracting the initial velocity from the final velocity, with velocities recorded with their direction signs before subtracting.AQA, OCR
Change in velocity (Δv): Found by subtracting the initial velocity from the final velocity, so Δv = v − u.AQA
change of speed: What happens when a wave enters a different substance, and the cause of the change of direction.AQA
change of speed in glass: Refraction happens because the light changes speed in the glass.AQA
change of state: What happens when the temperature stays constant while the energy goes to the potential store, separating the particles against the forces holding them…AQA
change of velocity: Found by subtracting the initial velocity from the final velocity, remembering that a rebound reverses the sign.AQA
changes in atomic number: Alpha decay reduces the atomic number of the nucleus by 2.AQA
changes in mass number: Alpha decay reduces the mass number of the nucleus by 4.AQA
Changes in stored energy during use: Match each rating to the store that changes, such as thermal energy of water or kinetic energy of a fan.OCR
Changes of state: Melting is solid to liquid, freezing is liquid to solid, boiling and evaporating are liquid to gas, condensing is gas to liquid, and sublimating is solid…AQA, OCR
changing and replacing models: Adapting or throwing out and rebuilding a model when an experiment produces a result the existing model cannot account for.AQA
changing direction: The direction of motion changing continuously, which means the velocity changes even though the speed does not.AQA, OCR
changing field: A change in the field through the coil, caused for example by a magnet sliding through a coil or a steel string vibrating above a magnet and a coil.AQA
Changing magnetic field: This is required in the core to induce a potential difference in the secondary coil.AQA
changing models: Scientists change the model when new evidence or observations appear that the existing model cannot explain.AQA
Changing potential difference in power transfer: Transformers are used in the transfer of power from power stations so that the potential difference is raised for transmission and lowered again for use.OCR
Changing speed or direction from an unbalanced force: If the forces do not balance, a resultant force exists and the speed and/or direction change.OCR
changing the strength: Its strength can be changed by increasing the current, adding more turns to the coil, or adding an iron core.AQA
Characteristic: Identified by varying the current or potential difference, recording pairs of readings and plotting a graph of current against potential difference.OCR
characteristic graph: A graph plotting current against potential difference that tells you what a component does.AQA
Charge: Measured in coulombs (C), it can be found by rearranging the equation to Q = E ÷ V.OCR
Charge as a universal property of matter: Charge is a property that every form of matter possesses, because matter is built from particles that carry charge.OCR
Charge carriers and transfer of electrons: Electrons, which carry negative charge, can be moved from one object to another when two different insulating materials are rubbed together.OCR
charge flow: Given by Q = I t, and it combines with E = Q V so that E = Q V = I t V = P t.AQA, OCR
Charge flow and current: Charge, current and time are linked by Q = I × t, where Q is charge in coulombs, I is current in amperes and t is time in seconds.OCR
charge flow equation: Charge flow, current and time are linked by the equation charge flow = current × time, or Q = I t.AQA
charge redistribution: Inside a neutral object the charges shift slightly, with the opposite charge drawn to the near side and the like charge pushed to the far side.AQA
Charge, current and time: The relation Q = I × t links quantity of charge, current and time.OCR
charging by friction: Rubbing certain insulating materials against each other makes them electrically charged, as electrons are dragged from the surface of one onto the surface of…AQA
Checking magnitude and units of an answer: Reasoning about direction and size before calculating, then checking the answer's units and magnitude.OCR
chemical change: A change that produces a new substance with its own properties, which is not recovered on reversal.AQA
choosing a half-life: A suitable half-life is long enough for the source to be useful but short enough that the activity does not persist and cause harm.AQA
Choosing appropriate apparatus: Matching each instrument to the quantity it measures, such as a ruler or metre rule for length and a balance for mass.OCR
Choosing appropriate measuring instruments: Selecting an instrument suited to the distance, such as a metre rule, tape measure or marked track, and a timing method suited to the interval, such as a…OCR
choosing materials: A material with a very high specific heat capacity is chosen so a huge energy transfer produces only a small temperature rise.AQA
Choosing suitable measuring apparatus: Apparatus suited to the wave and material is chosen, such as a ripple tank for water waves or a ray box and protractor for light.OCR
circular field around a wire: Around a long straight wire the field lines are circles centred on the wire, lying in a plane at right angles to it, and closest together near the wire.AQA
Circular field pattern around a straight wire: Around a straight wire the field lines are circles in a plane at right angles to the wire.OCR
Circular motion: Motion round a circle at constant speed, where the direction of motion changes continuously along the tangent to the circle.OCR
circular orbit: The path of a planet or satellite that is bent into a circle by a force at right angles to its motion.AQA
Circular orbits: A planet moves around a circle, and the gravitational force from the Sun acts towards the centre of the orbit.OCR
Clockwise and anticlockwise rotation: The two ways an object can turn; pushing the end of a spanner handle one way gives a clockwise turn and pushing the other way gives an anticlockwise turn.OCR
closed circuit: The other condition for charge to flow, forming a complete path so charge can travel all the way round.AQA, OCR
closed field lines: The internal and external lines join up, so each line is a closed loop through the coil and back round outside.AQA
closed loops: Inside the magnet the lines continue from south back to north, so every field line is a closed loop.AQA
closed system: A system on which no external resultant force acts, so nothing can add momentum to it or take momentum away.AQA
Closed systems: The number of particles and the volume are fixed, so the reasoning relating temperature and pressure is kept to these systems.OCR
Cochlea: Part of the ear where vibrations are converted into electrical signals sent to the brain.OCR
collision frequency: How often the molecules strike the container walls, which falls when the molecules are further apart and travel further between hits.AQA
collisions: When a moving object hits an obstacle, its kinetic store empties, mostly into thermal stores, with some energy transferred by sound waves.AQA
Collisions with container walls: Faster particles strike the walls more often and with greater force per collision, so the total force on a fixed area of wall increases.OCR
collisions with walls: Molecules hitting the walls of the container, which happens more often when the molecules move faster.AQA
colour coding: The insulation covering each wire is colour coded for easy identification.AQA
colour filters: A piece of coloured transparent material that transmits the wavelengths of its own colour and absorbs the rest, so the light that comes out is coloured and…AQA
Colour of objects in white light and in coloured light: The wavelengths that reach the eye determine the perceived colour, and a coloured surface under light of a different colour may appear black if that light…OCR
column of air: A body of air standing on a surface and reaching to the top of the atmosphere, every molecule in it having weight and pressing down on the surface.AQA
column of liquid: Its height, h, in metres, m, is multiplied by the density of the liquid and the gravitational field strength to give the pressure.AQA
combined mass: The mass used on the after side of the equation in a collision where objects join together.AQA
Combining fields of multiple turns: Winding the wire into a coil concentrates many turns so each turn's field adds to its neighbours' inside the coil, producing a much stronger, more uniform…OCR
combining forces: A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together.AQA
Communication and medicine: Uses including television and radio broadcasts, mobile phone signals, satellite and phone communications, medical imaging of bones and treating cancer.OCR
Comparing appliance ratings: A 2500 W heater warms a room faster than a 1000 W heater because it transfers energy at a greater rate.OCR
comparing at fixed pd: Two such components are compared at a chosen potential difference, since comparing them at different potential differences makes the comparison meaningless.AQA
Comparing devices of different power: Two devices transferring the same total energy differ in that the higher-power device does it in less time.OCR
comparing doses: Always convert both figures to the same unit before you compare or divide them.AQA
comparing galaxy spectra: Reading the dark lines of two galaxies so that the one shifted further towards the red end has the greater red-shift.AQA
comparing heights: Taking any two heights, where everything above the upper one is also above the lower one, and the lower surface carries the extra slab of air between them.AQA
comparing insulators: Judging which material has the higher thermal conductivity from the times taken to cool through the same temperature difference, where a shorter time means…AQA
comparing lines: On the same axes the steeper line is the faster one, and where the lines cross the two objects are at the same distance at the same time.AQA
comparing power: Two devices doing identical jobs at different speeds show that the one finishing in less time has the greater power.AQA
Comparing pressures at different heights: A point at sea level has a longer air column and greater pressure, while a mountain-top point has less air above it and lower pressure.OCR
comparing resources: This means naming the resources being compared and classifying them correctly as renewable or non-renewable, and comparing ways they are used for transport,…AQA
comparing storage methods: A genuine comparison links the two methods rather than describing them separately, holding both options together.AQA
comparison with a bar magnet: The field inside a solenoid is uniform, whereas the field around a bar magnet is never uniform.AQA
Compass needle as a small magnet: A needle that is a small magnet and turns freely, aligning with the local magnetic field.OCR
complete absorption: Because a black body neither reflects nor transmits incident radiation, all of that radiation is absorbed.AQA
complete circuit: The loop that must exist for there to be a current; without the neutral wire it is not complete.AQA
components equivalent to the force: The two component forces together have the same effect as the single force.AQA
Compound geometric shapes in physics: The space under a graph is split into simple geometric shapes, rectangles where velocity is constant and triangles where velocity changes uniformly.AQA
compressibility: A gas can be compressed because of the space between its particles, whereas a liquid can barely be compressed.AQA
Compressibility of gases: Gases can be compressed when the pressure on them is increased, reducing their volume.OCR
compression and expansion: A gas is compressed into a smaller volume when the pressure on it is increased, and expands when the pressure is lowered.AQA
compression and extension: The deformation of a spring, either squashed or stretched, on whose square the stored energy depends.AQA
compression by the air above: Air is a gas and can be compressed, so the weight of all the air above squeezes the air at the bottom into a smaller volume.AQA
compressions: Regions where the particles are pushed closer together and the pressure is higher than normal.AQA
compressions and rarefactions: A loudspeaker cone moving outwards pushes the air molecules in front of it together, creating a compression; as it moves back it leaves them further apart,…AQA, OCR
Computing rates: Identifying which quantity is divided by which, such as distance divided by time for speed.OCR
concentrated positive charge: What is somewhere inside the atom, repelling the small number of alpha particles that were deflected through large angles.AQA
concentration of mass: Most of the mass of an atom is concentrated in the nucleus.AQA
conduction: Energy carried through a material as vibrating particles jostle their neighbours and, in metals, as free electrons move through the structure.AQA
Conductor: A material that allows electric charge (electrons) to flow through it easily.Pearson Edexcel
conductors and insulators: The cores are copper because it is a good electrical conductor that bends without breaking, and each core is covered in plastic because plastic is an…AQA
cone and diaphragm: The cone or diaphragm is attached to the coil and moves with it, and the flexible surround lets the coil and cone move freely and spring back.AQA
conservation of charge: An emission equation is balanced when the atomic (proton) numbers on both sides agree, making the total charge on the left equal the total on the right.AQA, OCR
Conservation of energy: Total energy is conserved even though useful energy decreases, because dissipated energy is not destroyed but transferred to the surroundings.AQA, OCR
conservation of mass: A change of state rearranges particles; it does not create or destroy them, so the mass is the same before and after.AQA, OCR
conservation of mass number: An emission equation is balanced when the mass numbers on both sides agree, making the total on the left equal the total on the right.AQA, OCR
conservation of momentum: In a closed system, the total momentum before an event is equal to the total momentum after the event.AQA
consistent scale: When several vectors appear on the same diagram, draw them to a consistent scale so that a longer arrow really does mean a larger quantity.AQA
consistent units: Both pressures must share one unit and both volumes must share another, because the conversion factors cancel.AQA
Constant acceleration motion: Motion for which the equation links velocity, acceleration and distance without needing the time.OCR
constant and changing resistance: For some resistors the value of R remains constant, but in others it can change as the current changes.AQA
constant chance of decay: Every undecayed nucleus of a given isotope has the same constant probability of decaying in the next second.AQA
constant particle size: Every circle is kept the same size across all three diagrams because the particles themselves do not shrink or swell when a substance changes state.AQA
constant resistance: A fixed resistor keeps this because the ratio of potential difference to current stays the same as current changes.AQA, OCR
constant speed: The speed is steady, so the distance travelled in a specific time can be calculated using the equation.AQA
Constant speed with changing direction: The planet's direction of motion changes continuously around the circle, so its velocity changes even though its speed stays constant.OCR
constant speed with changing velocity: The satellite is accelerating all the way round and its velocity is changing all the way round, yet its speed stays constant.AQA
constant temperature: The condition that must hold for an ohmic conductor, so that current is directly proportional to potential difference.AQA
Constant temperature and constant average particle speed: At constant temperature the average speed of the gas particles stays the same, so the particles do not slow down when the volume increases.OCR
Constant temperature and fixed mass: The relationship applies only when both temperature and mass are held constant.OCR
constant temperature during melting: While the substance is changing state the temperature holds constant and the extra energy goes to the potential store instead.AQA
constant temperature plateau: A flat section of a heating curve, at the melting point or the boiling point, where a change of state occurs while the temperature stays constant.AQA
constant velocity: Moving at the same speed and in the same direction, which continues when the resultant force is zero.AQA, OCR
Constant velocity and rest: The motion of an object when the resultant force is zero, whether it stays at rest or moves at constant velocity.OCR
Constant velocity of all electromagnetic waves in space: In space all electromagnetic waves travel at the same velocity.OCR
Constant versus changing ratio: In a linear relationship the ratio of force to extension is constant, whereas in a non-linear relationship the ratio changes as force rises.OCR
constant volume: A gas is held at constant volume when it is sealed in a rigid container so the volume cannot change.AQA
Constructing and checking circuits from diagrams: To construct a circuit you read the diagram and join components in the order shown, keeping the loop closed; to check it, you compare the built circuit with…OCR
construction rays: Standard rays drawn from the top of the object to build a lens ray diagram; any two are enough to locate the image.AQA
Contact Force: A force that acts on an object by direct contact with it (e.g., friction, air resistance, normal reaction, tension).OCR
contact forces: Forces such as friction, tension, air resistance and the normal contact force that require the surfaces to touch.AQA
contact time: The time over which a person is brought to rest, which a safety feature increases so that the same change in momentum is spread over more time.AQA
contamination: The unwanted presence of radioactive material on or inside a person or object, which keeps delivering a dose for as long as the transferred atoms go on…AQA, OCR
Continuous range of electromagnetic radiation: A hot object emits a continuous range of wavelengths, so it emits photons with a continuous range of energies.OCR
continuous spectrum: The seven named groups are convenient labels along one unbroken range of wavelengths, not seven separate kinds of wave, with no gap between them.AQA
control rods: Usually boron, these absorb surplus neutrons without undergoing fission, mopping up the neutrons left over from each fission.AQA
control variables: The same water temperature, the same distance, the same starting temperature and the same time interval.AQA
controlling current: Changing the push by adding or removing cells or turning up a variable power supply, or changing the opposition by adjusting a variable resistor or adding…AQA
controlling variables: Describing a test in which only one of the two factors is changed at a time, keeping one variable fixed.AQA
conventional current: The current taken from positive to negative, which the second finger points along.AQA, Pearson Edexcel
Conventional current direction: The second finger points along the conventional current in the conductor.OCR
Conventional nuclear notation: A way of writing a nucleus with the mass number A as a superscript and the atomic number Z as a subscript, both before the element symbol.OCR
converging and diverging: A convex lens is converging and brings parallel rays together, while a concave lens is diverging and spreads parallel rays apart.AQA
converging versus diverging: Through a convex lens the rays converge, whereas through a concave lens they diverge.AQA
Conversion between joules and kilowatt-hours: One kilowatt-hour equals 1000 W multiplied by 3600 s, which is 3 600 000 J.OCR
Conversion from non-SI to SI units: Building a ratio from known equivalences and multiplying or dividing by that factor.OCR
converting back from a measurement: Reading a diagram reverses the process: measure the arrow, then multiply by the scale to give the magnitude.AQA
cooling curves: A graph on which a steeper section is linked to a greater rate of emission and which is steepest at the start and flattens off towards room temperature.AQA
Cooling of buildings: A warm building cools because energy is transferred through its walls to the cooler outside; the comparison concerns the rate, not the total energy, which is…OCR
Correct placement of measuring instruments: An ammeter is placed in series, and a voltmeter across a component.OCR
correlation and causation: A link shown in data does not automatically prove that the radiation caused the observed harm, so further evidence is needed to confirm the exact mechanism.AQA
Cosmic microwave background radiation: Faint microwave radiation arriving from every direction, interpreted as cooled remnant radiation from the early hot universe.OCR
coulombs: Charge flow, Q, is measured in coulombs, C.AQA
count-rate: The number of decays recorded each second by a detector such as a Geiger-Muller tube.AQA
counting neutrons: The upper number, the mass number, gives protons plus neutrons, so the neutron count is found by subtracting the atomic number.AQA
Counting squares: A method of finding the area under a curved or multi-section line by counting squares on the grid.AQA
couple on a coil: Two equal forces acting in opposite directions on either side of the axle, which turns the coil about its axle.AQA
coupling gel: A gel smeared on the skin to remove the air gap that would otherwise reflect almost the whole pulse at the surface.AQA
crossing a boundary: When a sound wave crosses from one medium into another, its frequency does not change, because the frequency is fixed by the source that made it.AQA
crossing point: The point where the construction rays cross, which is the top of the image.AQA
Current: The rate of flow of charge, measured in amperes (A), where one ampere is one coulomb per second.AQA, OCR
current and field strength: Increasing the current increases the strength of the magnetic field at any given point.AQA
Current and length in a field: I is the current in amperes and L is the length of conductor in the field in metres, multiplied with B to give force.OCR
current and power: Since the potential difference across the battery is unchanged, a rise in current raises the power output too, because P = I V.AQA
current as rate of flow of charge: The size of the electric current is the rate of flow of electrical charge.AQA
current balance: A demonstration in which the section of wire in the field moves down when the current flows.AQA
Current in a series loop: In a single closed loop, the current is the same at every point, so the same value is found at any point in the loop.OCR
Current paths and splitting: In parallel the current splits between alternative branches, giving more paths for charge to flow.OCR
Current versus energy transfer: Components transfer energy to the surroundings without reducing the current, so it is energy, not charge, that is transferred.OCR
Current–voltage characteristics: Graphs of current against voltage whose shape is used to identify a component and explain how its resistance behaves.OCR
curved characteristics: The graphs of such components are curved rather than straight because their resistance changes as conditions change.AQA
curved graphs: The shape of a distance-time graph for real motion, rather than a straight line, when speed changes.AQA
curved line: A line on either graph that shows changing speed or changing acceleration.OCR
curved ray paths: P-wave paths curve as the speed changes gradually with depth and kink where it changes suddenly.AQA

D

dam design: A dam is built much thicker at its base than at the top because pressure increases with depth.AQA
Danger of the live wire with an open switch: A switch in the live wire stops current when open, but the live wire on the supply side stays at a high potential relative to earth.OCR
dark energy: The term introduced for whatever is driving the accelerating expansion, because nothing in the existing physics explained it.AQA
dark mass and dark energy: Dark mass is needed to explain the way galaxies rotate, and dark energy is needed to explain the accelerating expansion; neither has been detected directly.AQA
data-supported conclusions: Conclusions backed by data, such as a longer time for the same temperature drop.AQA
decay in contact with tissue: Every decay of the contaminating atoms happens in contact with, or inside, living tissue, so the ionising radiation is absorbed by cells.AQA
deceleration: The rate of change of speed when speed decreases, found by dividing the change in speed between two points by the time taken between them.AQA, OCR
Deceleration and sign: A negative value simply means slowing down, so braking is treated as negative acceleration.OCR
Deceleration of vehicles: The change in velocity divided by the stopping time, calculated using a = Δv ÷ t with the change in velocity in m/s and the time in s.AQA
Decimal to percentage conversion: To change a decimal to a percentage, multiply by 100; to change a percentage to a decimal, divide by 100.AQA
decreasing acceleration: The resultant force is still downwards but smaller, so the object speeds up at a steadily decreasing rate.AQA
decreasing gradient: As the potential difference rises the filament heats, the resistance climbs, and the current no longer rises in proportion, so the curve bends over and its…AQA
Definition of potential difference: The energy transferred per unit charge, measured in volts (V), where one volt is one joule per coulomb.OCR
definition of ultrasound: Any sound with a frequency above the upper limit of human hearing.AQA
demagnetisation: The jumbling of the domains when a magnet is heated strongly, hammered or dropped repeatedly, so that it loses its magnetism.AQA
demonstrations with a wire: A wire resting on rails between the poles of a pair of magnadur magnets jumps when the switch is closed.AQA
Density: Measured in kilograms per metre cubed, kg/m, it is multiplied by the height of the column and the gravitational field strength to give the pressure.AQA, OCR
Density and depth: The pressure at a given depth depends on depth, density and g rather than on the cross-sectional area or volume of the container.OCR
Density as a property of a material: Depends on the material, not the size of the sample, so a larger volume of the same material has more mass but the same density.OCR
density comparison: Comparing the density of the object with the density of the fluid: if the object's density is lower, upthrust beats its weight and it rises.AQA, OCR
Density equation: Density equals mass divided by volume, written in symbols as ρ = m / V.OCR
density with altitude: The atmosphere gets less dense with increasing altitude, so the density falls steadily as you rise.AQA
Dependence of current on potential difference and resistance: Current depends on both the potential difference across a component and the resistance of that component.OCR
describing motion: Translating between graphical and numerical forms by describing the journey stage by stage, quoting specific times and distances from the axes.AQA
detecting a field: Placing a test object, such as a plotting compass, and watching for a force or a turning effect.AQA
detection and exploration: Sending a wave into a structure hidden from direct observation and reading what comes back, using differences in velocity, absorption and reflection.AQA
Detection by instruments: A detector such as a radio aerial, a thermal camera or a photographic film can register groupings the eye cannot detect.OCR
detectors: Devices such as an aerial for radio waves, a thermal camera for infrared, or a fluorescent material or photographic film for ultraviolet and X-rays, needed…AQA
diagonal is the resultant: The diagonal from that point is the single force equivalent to both.AQA
diaphragm: The part pushed in and out by the pressure changes, with a coil attached to it that moves with it in and out of the field of a permanent magnet.AQA
diaphragm and coil: The thin sheet facing the sound and the coil wound on a former fixed behind it, which vibrates with the diaphragm as sound waves arrive.AQA
diaphragms and drums: A microphone diaphragm, a loudspeaker cone and the ear drum all have a working range set by their size, mass and stiffness.AQA
dice model: Each die has a fixed one in six chance of showing a six on every throw and you cannot say which die will do it.AQA
diffuse reflection: Reflection from a rough surface, where the normals point in many different directions so parallel rays leave at many different angles and the light is…AQA
diode: One of the circuit elements whose I–V characteristics are investigated, and which needs a protective resistor in series so the forward current cannot damage it.AQA, OCR
diodes: Components through which current flows in one direction only and which have a very high resistance in the reverse direction.AQA
Dipping compass and vertical field component: A compass balanced so the needle can tilt in the vertical plane; away from the equator the needle dips downward because the Earth's field has a vertical…OCR
Direct and inverse proportionality: Identifying which quantity is directly proportional to which and which is inversely proportional.OCR
Direct Current (DC): An electric current that flows in one direction only.AQA
direct potential difference: Keeps the same sign, with one terminal staying positive, so charge in the circuit is pushed one way only.AQA
direct proportion: A relationship in which doubling the mass doubles the weight exactly, and trebling it trebles the weight.AQA
direct proportionality: The relationship where double the force gives double the extension, shown by a straight line through the origin on a graph of force against extension.AQA
Direct voltage: Keeps the same polarity, so the potential difference stays on one side of zero and current flows one way around the circuit.OCR
direction and sign: Choosing a positive direction first, so that where objects bounce apart one velocity is likely to be negative and the answer states the direction as well as…AQA
Direction convention: The chosen positive direction, which must always be stated because a negative value of u means motion in the direction chosen as negative.AQA
direction of a field: The direction of the force that would act on another north pole placed at that point.AQA
direction of energy transfer: The line along which a wave carries energy, to which transverse oscillations are perpendicular and longitudinal oscillations are parallel.AQA
direction of field lines: The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet.AQA
direction of force: Given by the field line at that point for a positive charge, while a negative charge feels a force in the opposite direction to the line.AQA
direction of rotation: Reversing the current, or swapping the magnetic poles over, reverses it, but doing both together changes nothing.AQA
direction of the force: The way each object in the interaction exerts a force on the other, which must be stated when describing an example.OCR
direction of the induced potential difference: Set by only two things, the direction of the relative motion and the direction of the magnetic field, and both of them are reversals.AQA
direction of transfer: Where force and displacement point the same way, energy flows into the object; where they point opposite ways, energy flows out of its kinetic store.AQA
Direction of vibration relative to direction of travel: The angle between vibration and travel: perpendicular for transverse, parallel for longitudinal.OCR
direction on a diagram: A weight arrow is drawn from the object towards the centre of the Earth, which on a diagram of a satellite in orbit is not simply 'down the page'.AQA
direction towards the centre: The weight of an object always acts towards the centre of the Earth.AQA
Directly Proportional: A relationship between two variables where if one doubles, the other also doubles.OCR
discovery of the electron: Thomson identified a particle far lighter than any atom and carrying a negative charge, so the idea that an atom could not be divided had to be abandoned.AQA
displaced fluid: The fluid an object has pushed out of the way, whose weight equals the size of the upward resultant.AQA
displacement: The vector partner of distance, carrying magnitude and direction, and zero for any journey returning to its start.AQA, OCR
displacement in the direction of a force: What counts is how far the object moves in the direction the force acts, not how far it travels altogether.AQA
Displacement method: Used for an irregular solid: record the water level in a measuring cylinder, lower the object in fully, and take the rise in level as its volume.OCR
displacement technique: A way of finding the volume of an irregularly shaped object by lowering it until it is fully submerged and collecting the water that overflows in a measuring…AQA
dissipation: Energy is spread out to the surroundings, too thinly spread to be recovered, as when friction in the bearings transfers energy into the thermal store of the…AQA
Dissipation of energy to the surroundings: Energy that is not useful output is dissipated to the surroundings, usually by heating.OCR
Distance: The total length of the path moved, a scalar quantity measured in metres (m).AQA
Distance along the line of action of the force: The distance measured along the line of action of the force, so only the part of the movement in the direction of the force counts.OCR
distance and displacement: A kinematic scalar paired with the vector partner that does carry direction.AQA
Distance and displacement from motion graphs: The separate calculated areas are added together to obtain the total distance travelled, giving the final answer with the unit m.AQA
distance equation: Distance travelled equals speed multiplied by time, with distance in metres, speed in metres per second and time in seconds.AQA
distance from the magnet: The field gets weaker as the distance from the magnet increases, and the weakening is sharp rather than proportional.AQA
distance from the wire: The field is weaker at greater distances from the wire, which is why the concentric circles are drawn further apart further out.AQA
distance travelled: The quantity calculated from the area under a velocity–time graph, or from the area below the time axis for motion in the opposite direction.AQA, OCR
distance-time graph: A graph on which the slope gives speed: a horizontal line means the object is stationary, a straight sloping line means constant speed, and a steeper line…OCR
Distinguishing extension from total length: The change in length from the natural length, not the total length, so subtract the original length first.OCR
Distinguishing force from mass: Force is recorded in newtons, not kilograms, and weight is a force while mass is not.AQA
distractions: Things such as a phone that may affect a driver's ability to react, adding time before the driver's foot reaches the brake pedal.AQA
Distribution of mass in the atom: Almost all of the mass of the atom is concentrated in the nucleus.OCR
distribution of the elements: The throwing of all of a star's elements outwards into space, so they mix into the clouds of dust and gas between the stars.AQA
diverging lens: A concave lens spreads apart rays that arrive parallel to the principal axis, as though they had come from a point on the same side as the object.AQA
divisible atoms: The atom must contain smaller parts, so it is not indivisible.AQA
DNA damage: Ultraviolet radiation damages the DNA inside skin cells, and this genetic damage can cause mutations.AQA
do not cancel: The two forces act on different objects, so they never cancel each other out.OCR
domains lining up: The external field lines up the magnetic domains inside the material, so it develops its own north and south poles.AQA
domains randomising: Without the field to hold them, the domains fall back into a random arrangement and the poles disappear.AQA
dose monitoring: Workers are monitored with film badges or electronic dosimeters and work to legal dose limits.AQA
dose versus activity: Dose describes the risk of harm to body tissue from being exposed to radiation, while activity counts decays per second in the source.AQA
dotted projections: Tracing the emerging rays backwards with dotted lines shows where they appear to come from, and that is the virtual image.AQA
dotted virtual rays: Rays traced backwards as dotted lines behind a concave lens to find the virtual image.AQA
double insulation: An appliance with a plastic case, such as a hairdryer or a phone charger, uses a two-core cable because a plastic case cannot become live even if a wire works…AQA
drag: As the object speeds up, fluid resistance grows, and the resultant force is now weight minus drag and upthrust if in a liquid.AQA
driving force: The force from the wheels that pushes a vehicle forward.AQA
duration of exposure: Irradiation stops when the source is removed or shielded, whereas contamination continues while the atoms decay, which for a long half-life can be years.AQA
dwarf planets: These orbit the Sun but have not cleared other objects out of their orbital path, so they are counted separately from the planets.AQA
dynamo: A machine that uses the generator effect to generate dc, spinning a coil in a magnetic field with a single split-ring commutator.AQA

E

E = m L: The equation for the energy for a change of state, where energy is in joules, mass in kilograms and specific latent heat in joules per kilogram.AQA
E = P t: The relationship used to find the energy transferred over a given time, giving joules when time is in seconds.AQA, OCR
E = Q V: The equation used to calculate energy transferred, where energy transferred equals charge flow multiplied by potential difference.AQA
ear drum: Part of the ear that pressure variations in air push on, so that it vibrates and the ossicles pass the vibration to the cochlea.AQA
Eardrum: A thin membrane in the ear that sound waves strike and cause to vibrate.OCR
earth as 0 V: The earth is taken as the zero of potential, so its potential is 0 V.AQA
earth wire: A safety wire connected to the metal case of an appliance that carries no current in normal use but provides a low-resistance path to earth if a fault occurs.AQA, OCR
earth wire at 0 V: The earth wire sits at 0 V, so in normal operation both ends are at 0 V and there is no potential difference along it.AQA
Earth's magnetic field: The field the Earth behaves as though it has, which a plotting compass held horizontally aligns with, so its needle points roughly north–south.AQA, OCR
Earthing: The process of removing excess charge by providing a low-resistance path for electrons to flow to or from the Earth.Pearson Edexcel
Easily magnetised: Iron is used as it is easily magnetised, so its magnetism can follow a magnetic field that changes direction rapidly.AQA
echo pulses: Separate pulses on the detector trace, each returned a little later by its own deeper boundary as the pulse passes through layered tissue.AQA
echo sounding: Using high frequency sound waves to detect objects in deep water and measure water depth.AQA
echo timing: A short pulse is sent out, travels to the boundary, reflects and travels back, and the detector records the time between transmission and echo.AQA
echoes: Sound travels to the wall and back, so the distance in the equation is twice the separation.AQA
effect of separation: The size of the force grows quickly as the separation is reduced and as stronger magnets are used.AQA
Effect of shape and hollowness: Shape sets the volume displaced when fully submerged, so a hollow steel hull floats while a solid steel block sinks.OCR
effect of temperature: In a filament lamp the current itself heats the filament, and a hotter filament resists more.AQA
Effect of the atmosphere on electromagnetic radiation: Incoming short-wavelength radiation from the Sun passes through the atmosphere, while the Earth emits longer-wavelength infrared, some of which the atmosphere…OCR
effect on normal contact force: The vertical component effectively lifts the sled and so reduces the normal contact force from the surface, which in turn reduces the friction.AQA
Efficiency: Compares the useful energy or power transferred by a device with the total energy or power supplied to it, and is always between 0 and 1, or between 0% and…AQA, OCR
Efficiency as a ratio and percentage: Useful energy output divided by total energy input, giving a value between 0 and 1, and multiplying by 100 gives a percentage.OCR
efficiency of conversion: Converting a sound wave into vibration of a solid, and back again, is efficient only over a limited frequency range.AQA
efficient appliances: Devices that need a smaller energy input for the same useful output, so less electricity has to be generated.AQA
elastic deformation: Occurs when the object returns to its original length and shape once the stretching force is removed, so the change is reversible.AQA, OCR
Elastic limit: The point beyond which a spring no longer returns to its original length when unloaded, meaning inelastic deformation has occurred.AQA, OCR
Elastic limit and material behaviour: A material may behave elastically for small forces and plastically once the force exceeds its elastic limit.OCR
Elastic limit and permanent deformation: Beyond the elastic limit the line curves and the spring is permanently deformed, so the simple proportionality no longer holds.OCR
Elastic potential energy: The energy associated with a stretched spring, given by E_e = ½ × k × x², where k is the spring constant in N/m and x the extension in metres.AQA, OCR
elastic potential store: The energy stored in a stretched spring, calculated as Eₑ = ½ k e², with e the extension in metres, not the total length.AQA
Electric charge of nucleus and electrons: The nucleus is positively charged and the electrons are negatively charged.OCR
electric field: The region around a charged object where another charged object experiences a force.AQA, OCR, Pearson Edexcel
electrical heating: Bringing water to a boil in an electric kettle involves the mains doing electrical work, filling the thermal store of the water and of the kettle itself.AQA
electrical neutrality: Atoms have no overall electrical charge because the positive and negative charges cancel exactly.AQA
Electrical power: The rate of energy transfer, measured in watts, where 1 W equals 1 J transferred each second.OCR
Electrical work: Work done when a current flows, transferring energy electrically, where the energy transferred depends on current, potential difference and time, related by E…OCR
electrical working: Energy transferred when a current flows, calculated using E = P t or E = Q V.AQA
electricity generation: One of the uses of energy resources, alongside transport and heating.AQA
electromagnet: A solenoid, or coil of wire, with an iron core, whose magnetic field is present only while there is a current in the coil.AQA
Electromagnetic induction: When the magnetic field around a conductor changes, a potential difference is induced across its ends.OCR
Electromagnetic spectrum: The range of regions whose practical uses depend on wavelength and energy, covering radio, microwave, infrared, visible, ultraviolet, X-ray and gamma ray.OCR
Electron: A negatively charged subatomic particle that can be transferred between objects to create static charge.Pearson Edexcel
electron arrangement: The way electrons are arranged at different distances from the nucleus, filling the lowest energy level first, such as 2,8,1 for sodium.AQA
electron energy changes: Changes in the electrons of an atom, where an electron moves between energy levels, produce waves in the infrared, visible, ultraviolet and X-ray parts of the…AQA
Electron energy levels: In each atom its electrons are arranged at different distances from the nucleus, with inner levels closer and lower in energy.OCR
electron shells: The particular distances from the nucleus that electrons occupy, drawn as shells and described as energy levels.AQA
electron transfer: Only electrons move when materials are rubbed together, because the positive nuclei are fixed, so charge is transferred between the materials rather than…AQA
electrons: Negatively charged particles that surround the nucleus, each with a relative charge of -1.AQA, OCR
electrostatic force: The attraction and repulsion between two charged objects, one of the three non-contact forces alongside the gravitational and magnetic forces.AQA
Electrostatics: An interaction between charged objects, such as a charged rod attracting small pieces of paper.OCR
element identity: The number of protons fixes which element the atom is, so six protons is always carbon.AQA
elements from a supernova: Elements heavier than iron are produced in the enormous energies of a supernova explosion instead of in a star's core.AQA
embedded electrons: Negatively charged electrons sit within the positive charge like fruit in a pudding.AQA
emergency stopping: Bringing a road transport vehicle to rest in an emergency, where the distance required depends on factors that affect the thinking distance and the braking…AQA
Emission: When the electron loses energy it is emitted as radiation as the electron falls to a lower level.OCR
emission and absorption: An atom can give out a wave or absorb a wave of the right frequency and move to a higher energy level.AQA
Emission and absorption of electromagnetic radiation: Incoming radiation of a suitable frequency can be taken up and change the atom or nucleus, while changes can also generate radiation.OCR
emission into space: The rate at which infrared is emitted back into space is one factor the Earth's temperature depends on.AQA
emitted particle numbers: The emitted particle is treated as a full member of the totals, with its own two numbers, and the -1 on a beta particle has to be included when the atomic…AQA
empty space: What the atom must be mostly made of, because most alpha particles passed straight through undeflected.AQA
Energy change: The change produced by a device, such as thermal energy in a resistor or light and thermal energy in a lamp.OCR
Energy change and internal energy: When a material is heated without changing state, its change in internal energy equals the energy supplied.OCR
Energy dissipation: The spreading of energy into the surroundings, usually by heating, so that it becomes stored in less useful ways.OCR
Energy dissipation in transfers: The remaining energy that is not useful output, dissipated mainly by heating the surroundings.OCR
energy in joules: The energy stored by lifting an object, given in joules, as in 60 × 9.8 × 4.5 = 2646 J.AQA
energy levels: The different distances from the nucleus at which electrons are arranged, with the level closest to the nucleus being the lowest in energy.AQA
energy not matter: Both types of wave transfer energy without transferring matter.AQA
Energy of radiation: The missing mass appears as this, often carried away by a fast neutron and gamma rays.OCR
energy pathways: Mechanical working, electrical working, heating or radiation, by which energy moves between stores.AQA
energy redistribution: A change in a system is a redistribution between stores, never a creation or destruction of energy.AQA
energy released on cooling: The same energy that heating the object would need, because the equation works both ways.AQA
energy released per fission: Each fission event transfers energy from the nuclear store of the fuel, and per atom this is roughly a million times more than any chemical reaction such as…AQA
energy source of stars: Fusion is the energy source of every main sequence star, where its outward effect balances the inward gravitational collapse.AQA
Energy stored by raising a mass: Energy stored when a mass is raised against gravity, calculated as mass times gravitational field strength times height.OCR
Energy stored in a system: The energy stored in the thermal store increases when heating transfers energy into the system.OCR
energy stores: Kinetic, gravitational potential, elastic potential, thermal, chemical, magnetic, electrostatic and nuclear, between which energy moves.AQA
Energy stores and transfers: For each named situation, track the store that empties and the store that fills as energy moves between them.OCR
energy transfer: Energy, not matter, moves from the source to the absorber, and when the wave is absorbed the energy is transferred to another store.AQA, OCR
Energy transfer and braking: Brakes convert kinetic energy into thermal energy, and very large decelerations can overheat brakes and reduce their effectiveness.AQA
Energy transfer and particle kinetic energy: Energy transferred to the gas by work increases the kinetic energy and average speed of the particles.OCR
Energy transfer between stores: The work done by the pushing force transfers energy from the person to the box's kinetic energy store, and friction transfers energy by heating to the…OCR
Energy transfer by heating: Heating transfers energy into the system and increases the energy stored in its thermal store.OCR
Energy transfer by waves: Electromagnetic waves carry energy and transfer it from a source to an absorber, while no material travels with the wave.OCR
Energy transfer measured in joules: Work done measures the energy transferred when a force moves an object, and the unit of work done is the joule.OCR
energy transfer on release: The emptying of the elastic store into whatever the spring pushes, such as a kinetic or gravitational potential store.AQA
energy transfer to thermal store: The fast-moving fission fragments collide with surrounding atoms in the fuel rods, transferring energy to the thermal store of the fuel.AQA
Energy transferred: Equals power multiplied by time, given in joules when power is in watts and time is in seconds, or in kilowatt-hours when power is in kilowatts and time is in…OCR
energy transferred by current flow: Calculated as E = P × t or E = Q × V, with power in watts and time in seconds giving joules.OCR
Energy transfers between stores: Energy moving from one store to another, such as gravitational potential to kinetic, while the total stays constant.OCR
Energy versus matter: The key idea is energy moving from source to absorber, not matter moving.OCR
Energy, mass and specific latent heat relationship: E = m × L, where E is the energy change in joules, m is the mass in kilograms and L is the specific latent heat in joules per kilogram.OCR
environmental impact: This arises from the use of different energy resources, such as carbon dioxide from burning, radioactive waste from nuclear, flooded valleys from…AQA
environmental issues: Problems that may arise from the use of different energy resources, such as carbon dioxide released when fossil fuels burn and its link to global warming.AQA
equal and opposite: The size of the positive charge is exactly equal to the negative charge picked up by the other material.AQA
equal and opposite charges: The two objects end up with equal and opposite charges: whatever one gains, the other has lost.AQA
equal and opposite forces: By Newton's third law the magnet is pushed back with an equal and opposite force, which is why a magnet resting on a balance shows a change in reading when…AQA
equal and opposite pairs: The rule that the two forces are equal in size and opposite in direction, and each is a vector.AQA
equal angles: The angle of reflection is equal to the angle of incidence, both measured from the normal.AQA
equal current: The current in the neutral wire is exactly the same size as the current in the live wire, since the appliance does not use charge up.AQA
Equal numbers giving zero net charge: In a neutral body the total amount of positive charge equals the total amount of negative charge, so the charges cancel and the net charge is zero.OCR
equal reflection: Reflecting all wavelengths equally, which makes an object appear white.AQA
Equation for power: Power (W) = work done (J) / time (s), linking work done in joules, time in seconds and power in watts.OCR
Equation for pressure: p = F ÷ A, which can be rearranged to F = p × A or A = F ÷ p.AQA
Equation linking acceleration, velocity change and time: Acceleration equals change in velocity divided by time taken, giving average acceleration over the time interval.AQA
Equation linking motion quantities without time: v² − u² = 2as, where v is final velocity in m/s, u is initial velocity in m/s, a is acceleration in m/s² and s is distance in m.AQA
Equilibrium: The inward gravitational force equals the outward pressure from fusion, so the star remains at a constant size.AQA, OCR
equilibrium and closed triangles: Three forces acting on an object with a zero resultant form a closed triangle when drawn tip to tail, so if the drawing does not close the forces are not…AQA
Equilibrium between collapse and expansion: Energy released in fusion raises the pressure and pushes outward while gravity pulls inward, and when the two balance the star is in equilibrium.OCR
Equilibrium from balanced forces on one object: A book resting on a table is in equilibrium because the upward push of the table on the book balances the downward pull of gravity on the book, both acting on…OCR
Equilibrium with zero resultant: Shown when vectors close to form a complete shape, giving zero resultant.OCR
equivalent points: Matching points on neighbouring waves, such as crest to the next crest, trough to the next trough, or compression to the next compression.AQA
Equivalent resistance in series: For resistors in series the same current flows through each resistor, the p.d.s add, and the equivalent resistance is R = R₁ + R₂ + … .OCR
errors carried forward: A rule under which values carried forward from an earlier part are credited, so a wrong number early on does not automatically cost every mark that follows.AQA
estimating: Using sensible values and rounding, not quoting exact figures.OCR
Estimating physical quantities: Choosing sensible values for mass, initial speed and stopping time, then giving the answer to a reasonable number of significant figures.AQA
estimation: Using an estimated or typical value rather than a precise calculation, as when a question provides or asks for an estimate.AQA
evaluating evidence: Recognising that evidence and decision making are different things, since scientific evidence alone does not settle what happens next.AQA
everyday accelerations: The magnitude of accelerations for situations such as a family car pulling away, a sports car, a sprinter, a commuter train or a passenger lift.AQA
Everyday energy changes: In common situations, such as a rising object, a collision, a slowing vehicle or a kettle, energy is transferred between kinetic, gravitational potential,…OCR
Everyday example of a bicycle pump: Compressing the air inside as the piston moves in warms the air and the pump barrel feels warm to touch.OCR
everyday examples: Examples used to illustrate the balance between incoming radiation absorbed and radiation emitted.AQA
Everyday transport speeds: Typical figures such as walking about 1.5 m/s, running about 3–6 m/s, cycling about 5–10 m/s, a motorway car about 30 m/s and a train about 50–60 m/s.OCR
evidence: A specific observation, such as a cork bobbing, that shows the wave and not the water or air itself travels.AQA
Evidence for a magnetic core: The consistent alignment and dip of compass needles at many places on the Earth's surface are evidence that the Earth has its own magnetic field, which is…OCR
Evidence for an expanding universe: The pattern of speed increasing with distance is evidence that the universe is expanding.OCR
evidence for non-contact forces: A charged rod brought near another suspended charged rod shows like charges repel and opposite charges attract without touching.AQA
evidence for the Big Bang: Running the expansion backwards shows everything was once together, which is what the Big Bang theory describes.AQA
Evidence from floating objects on water: A floating object such as a cork bobs up and down as the ripple passes but stays in roughly the same place, so the water oscillates while the ripple pattern…OCR
Excitation: An inner electron absorbs energy from electromagnetic radiation and rises to a higher energy level.OCR
expanding universe: The conclusion drawn from the change of each galaxy's speed with distance, where the further away a galaxy is the faster it recedes and space is expanding…AQA
Expansion and compression by pressure change: A gas can expand when the pressure on it is reduced, increasing its volume, and can be compressed when the pressure is increased.OCR
Expansion and cooling of the universe: An initial hot dense state followed by expansion and cooling, which together explain the observations.OCR
experimental evidence: The idea came from experimental evidence, not from theory alone, which is why it took further work after the nuclear model was established.AQA
Experimental method: A procedure in which one person holds a ruler vertically and releases it without warning while another catches it between thumb and finger.OCR
Explaining density differences using the particle model: A given volume holds many particles when they are packed tightly, giving high density, and far fewer particles when they are far apart, giving much lower…OCR
Explaining mechanisms: Heating changes how easily charge carriers move through the material, altering resistance, so the shape of the graph is linked to whether resistance is…OCR
explaining non-contact force: The first object fills the space around it with a field and any charge placed in that space feels a force, so nothing has to reach across the gap.AQA
explaining refraction: Refraction is the consequence of one part of the wave slowing before another, so the front pivots and the whole wave changes direction.AQA
exposure stops on removal: The exposure ends as soon as the source is removed or shielded.AQA
exposure time: The time of exposure, on which the dose depends.AQA
extension: The stretched length minus the original unstretched length, so a spring 30 mm long that becomes 50 mm long has an extension of 20 mm.AQA, OCR
extension and compression: The amount by which an elastic object gets longer, or how much shorter it has become, measured in metres and given the symbol e.AQA
extra layer of air: The slab of air between two heights that sits above the lower surface only, so a lower surface carries it compared to a higher one.AQA
extreme temperature and pressure: Only the enormous temperature and pressure in a star's core give the nuclei enough kinetic energy to collide and join.AQA

F

F = B I l: The equation for a conductor at right angles to a magnetic field and carrying a current, where force = magnetic flux density × current × length.AQA
F = m a: Equation linking the resultant force in newtons, the mass in kilograms and the acceleration in metres per second squared.AQA
falling through a fluid: An object falling through a fluid initially accelerates due to the force of gravity.AQA
fault current: A very large current that passes through the live wire and the earth wire when the live wire works loose and touches the metal case.AQA
field across the gap: The field in the gap runs across the coil, so the force on the coil acts along the axis of the cone, in or out.AQA
Field around a bar magnet: The lines crowd near the poles and spread out further away, so the field is strongest at the poles and weakest at the sides and at distance.OCR
field around a magnet: It exists in three dimensions whether or not anything is there to feel it, is strongest at the poles, and gets weaker with distance.AQA
field around a straight wire: Two things set its strength: the size of the current and the distance from the wire.AQA
field between like poles: The lines leaving both north poles bend away from each other, and none of them run from one magnet to the other.AQA
field inside a solenoid: A strong and uniform field, where away from the two ends the field lines run parallel to the axis, evenly spaced and all pointing the same way.AQA
field line conventions: Lines must never cross, and they should be drawn closer together near the surface to show the stronger field there.AQA
field line diagrams: The same diagram conventions serve both electric fields and the magnetic field of a bar magnet, which also weakens with distance from the poles.AQA
field line spacing: The spacing of the field lines is linked to the strength of the field, with lines packed closest together at the poles and spreading out as you move away.AQA
Field lines: Lines representing a field, whose direction shows the force on a positive charge and whose spacing shows the strength of the field.OCR
field lines between poles: The lines leave the north pole of one magnet, cross the gap and enter the south pole of the other, and are tightly packed in the gap because the field there…AQA
field of the induced current: The induced current makes a magnetic field of its own, and that field always opposes whatever caused it.AQA
field pattern of a solenoid: Parallel evenly spaced lines inside that loop round outside like a bar magnet's, with an arrowhead on every line and the current direction marked.AQA, OCR
field pattern of a straight wire: Concentric circles round the wire, widening with distance, with an arrowhead on every line and the current direction marked.AQA
field strength: Depends on the distance from the magnet, being strongest at the poles and getting weaker as the distance from the magnet increases.AQA, OCR
Field strength and current: The strength of the field increases as the current through the conductor increases, so a larger current gives a stronger field.OCR
field strength and distance: The further away from the charged object, the weaker the field, so a charge placed far from the object feels only a small force.AQA
Field strength and distance from the conductor: The strength of the field decreases as the distance from the conductor increases, so the field is strongest close to the wire.OCR
Field strength and line spacing: Lines drawn close together mark a strong field, while widely spaced lines mark a weak field.OCR
field weakens with distance: The field is strongest at the surface and gets weaker with distance, so the field strength, and so the weight, decreases as distance from the Earth increases.AQA
field, current and force: The three directions related by the rule: the first finger points along the field, the second finger along the current and the thumb gives the direction of…AQA
filament lamp: One of the circuit elements whose I–V characteristics are investigated in the required practical.AQA, OCR
filament lamps: A lamp in which current in the thin metal filament raises its temperature until it glows.AQA
Final velocity: The velocity of an object at the end of the time interval or displacement being considered, having both magnitude and direction.AQA
finite: Of limited supply, so that using the resource uses it up.AQA
fire alarms: A sudden rise in temperature produces a sudden fall in resistance that triggers the alarm.AQA
fissions per second: The power output depends on the number of fissions per second, so controlling how many neutrons go on to cause further fissions is exactly how the output of a…AQA
fitness: A trained person sustains a higher speed for longer before fatigue forces them to slow down.AQA
fixed magnet: The permanent magnet fixed to the body, whose magnetic field lines are cut by the moving coil.AQA
fixed mass of gas: The relationship only holds while the temperature and the mass of gas stay fixed.AQA
fixed nuclei: The positive nuclei are locked in place in the solid.AQA
fixed orbits: The certain fixed distances from the nucleus that electrons can only occupy, rather than any distance at all.AQA
fixed poles: The north and south poles of a permanent magnet, which stay in place so that it can repel as well as attract.AQA
fixed resistors: A component whose resistance stays constant as the current changes, so it behaves predictably whatever the circuit does to it.AQA
Fixed speed of electromagnetic waves: The electromagnetic spectrum is one family of transverse waves that all travel at the same speed in a vacuum, about 3.0 × 10⁸ m/s.OCR
Fleming's left hand rule: A rule that represents the relative orientation of the force, the current in the conductor and the magnetic field, using the thumb, first finger and second…AQA, Pearson Edexcel
floating and sinking: An object floats when it can displace a weight of fluid equal to its own weight before it is fully under, and sinks when its density is higher than the fluid's.AQA
floating objects: A floating object bobs up and down as ripples pass but stays in the same place, showing the water does not travel with the wave.AQA
Fluid: A liquid or a gas, which exerts pressure on any surface it is in contact with.AQA
Fluid pressure: In a fluid, a liquid or a gas, pressure causes a force that acts at right angles (normal) to any surface it contacts.AQA
fluids: Substances that can flow, covering both liquids and gases and excluding solids.AQA
Fluids as gases and liquids: A fluid is any substance that flows, so both gases and liquids count.OCR
focal length: The distance from the lens to the principal focus, measured from the centre of the lens to the principal focus.AQA
force: Estimated by applying F = ma with a sensible vehicle mass, and quoted in N or kN.AQA, OCR
Force and acceleration: For a fixed mass, a larger deceleration requires a larger force, as shown by F = m × a.AQA
Force and area relationship: Pressure increases if the force increases or if the area decreases, for a constant value of the other variable.AQA
Force and extension proportionality: Extension increases as the applied force increases, and in the straight-line region doubling the force doubles the extension, so force divided by extension…OCR
force and separation: The force gets stronger as the distance between the objects decreases.AQA
Force as a vector quantity: Force has size and direction, and the direction of the resultant force determines the direction of the acceleration.AQA
force at right angles: The net force a gas produces acts at right angles to the wall of its container or any surface, whatever the wall's orientation.AQA
force between charges: When two electrically charged objects are brought close together they exert a force on each other.AQA
force between magnets: When two magnets are brought close together, each one exerts a force on the other.AQA
Force direction and orientation: The force is greatest when the conductor is at right angles to the magnetic field and is zero when it is parallel to the field.OCR
Force multiplication: The ratio of the effort arm to the load arm sets the force multiplication, so a long effort arm and short load arm turn a small force into a large one.OCR
force multiplier: A device that trades force against distance or speed, since the energy transferred is not increased.AQA
force on a conductor: When a conductor carrying a current is placed in a magnetic field, the magnet producing the field and the conductor exert a force on each other.AQA
Force on a current-carrying conductor: The force in newtons equals magnetic flux density in tesla multiplied by current in amperes multiplied by the length of conductor in metres within the field.OCR
Force pairs acting on different objects: The two forces act on different objects, so they never cancel each other.OCR
force per collision: Each molecule hits a wall harder, exerting a greater force during each collision.AQA
force per unit area: The total force of the collisions shared over the wall area, which falls when the force is spread over a larger surface area.AQA
Force perpendicular to surfaces: Because particles arrive from all directions inside the gas, the combined effect is a net force acting at right angles to every surface the gas touches.OCR
force through a field: The field of one magnet reaches the other and exerts a force on it, and the second magnet's field does the same in return.AQA
force towards the centre: The gravitational attraction that pulls a satellite towards the centre of its orbit rather than along its path.AQA
force-extension graph: A plot of force on the vertical axis against extension on the horizontal, whose gradient of the straight part is the spring constant.AQA
force–extension line: A straight line through the origin in linear cases, whose gradient also equals k.OCR
Force, mass and acceleration: The resultant force is estimated by substituting the mass and the deceleration into F = m × a, with the unit stated as N.AQA, OCR
Force, mass and acceleration proportionality: Doubling the force on a fixed mass doubles the acceleration, while doubling the mass under a fixed force halves it.OCR
Forces and acceleration: A non-zero resultant force causes the object to accelerate in the direction of that resultant.OCR
Forces and motion: In the absence of air resistance all objects fall with the same acceleration regardless of mass.AQA
Forces and shape change: To stretch, bend or compress an object, more than one force has to be applied, because a single force simply accelerates the object in the direction of the…OCR
forces as vectors: A force is drawn as an arrow from the object in the direction the force acts, exactly like any other force.AQA
Forces between charged objects: Two objects carrying like charges repel; two carrying opposite charges attract.OCR
Formation of the Sun from dust and gas: Our Sun was formed from dust and gas drawn together by gravity.OCR
forward and reverse direction: The two ways a diode can be connected, with current passing in one direction only and the resistance being very high in the reverse direction.AQA
fossil fuels: Coal, oil and gas, which are finite and so non-renewable, and which dominate transport and heating.AQA, OCR
fraction not number: Equal time intervals remove equal fractions rather than equal numbers, which is exactly what produces a fixed half-life.AQA
free body diagram: A diagram that isolates one object and shows only the forces acting on that object, each drawn as a labelled arrow starting on the object.AQA, OCR
Free body diagrams: A diagram showing the object as a point or simple shape with one arrow for each force acting on it.OCR
Free body force diagram: A diagram that isolates one object and shows every force acting on that object as an arrow, with length representing magnitude and arrowhead giving direction.OCR
Free fall: Motion under gravity alone, with air resistance negligible.OCR
free fall as a yardstick: Anything dropped near the Earth's surface accelerates at about 10 m/s² while air resistance is small, and that value is the natural yardstick for comparison.AQA
Free-fall acceleration: A dropped object accelerates at about 10 m/s² due to gravity, and this is the benchmark for sanity-checking answers.OCR
Frequency: The number of complete waves passing a point each second, measured in hertz.AQA, OCR
Frequency (f): The number of complete waves passing a certain point per second.OCR
frequency and wavelength: Red has the longest wavelength and therefore the lowest frequency, violet the shortest wavelength and the highest frequency.AQA
Frequency matching between wave and circuit: The frequency of the emitted wave matches the frequency of the current oscillation, and the induced oscillation has the same frequency as the incoming wave.OCR
frequency of collisions: Each molecule reaches the walls more often, so collisions with the walls become more frequent.AQA
Frequency of the UK mains supply: The frequency of that reversal is 50 Hz, meaning 50 complete cycles every second, so the direction changes 100 times per second.OCR
frequency unchanged: The frequency stays the same when the sound crosses the boundary, because it is fixed by the source that made it.AQA
friction: The force available at the tyres and at the brakes, which is lowered by a film of water or ice between tyre and surface.AQA, OCR
Friction and heating to surroundings: Friction or air resistance transfers energy by heating to the surroundings and reduces useful energy.OCR
friction and insulators: Static electricity is produced when two different insulating materials are rubbed together, and friction causes electrons to be transferred between them.AQA
friction and internal energy: Work done against friction raises the internal energy of the objects, so naming friction alone is not enough.AQA
friction and lubrication: Oil the bearings and less work is done against friction, so a greater proportion of energy is transferred usefully.AQA
friction removing energy: Where force and displacement point opposite ways, as with friction on a sliding box, energy flows out of its kinetic store instead.AQA
further enquiry: Publication promotes further enquiry, prompting new experiments and new explanations.AQA
fuse melts: The surge melts the fuse in the live line, which disconnects the live supply and leaves the case safe to touch.AQA
fusion and vaporisation: Fusion is the solid to liquid change and vaporisation is the liquid to vapour change.AQA
Fusion reactions releasing energy: When the core is hot enough, hydrogen nuclei fuse to form helium, releasing energy.OCR

G

galaxy: A very large collection of stars held together by gravity.AQA
gamma cameras: A detector outside the body that receives gamma radiation passing out of the body and builds an image of how the organ is working.AQA
gamma emission: The emission of a gamma ray, which does not cause the mass or the charge of the nucleus to change.AQA
Gamma radiation: A high-energy electromagnetic wave with no mass and no charge, so it changes neither mass number nor proton number.OCR
gamma ray: Electromagnetic radiation from the nucleus, with no mass and no charge.AQA, OCR
Gamma rays as an example of nuclear radiation: A change inside a nucleus can emit gamma radiation, which is one important example.OCR
gamma rays emitted: The electromagnetic radiation emitted as the excited fragments settle after the nucleus splits.AQA
Gas pressure and volume: For a fixed mass of gas at constant temperature, pressure multiplied by volume stays constant, written p × V = constant.OCR
gears: Meshing gears transmit rotational effect, and the ratio of teeth numbers sets the force multiplication, with a larger driven gear increasing turning effect…AQA, OCR
Geiger-Muller tube: A detector that records the number of decays each second.AQA
gene mutation and cancer: Knocking electrons off atoms can cause the mutation of genes and lead to cancer.AQA
generations of fission: The sequence continuing from a first fission to a second and then a third generation of fissions.AQA
generator effect: The effect used by microphones to convert the pressure variations in sound waves into variations in current in electrical circuits.AQA
gloves: A precaution that prevents transfer of material even though it does not stop irradiation.AQA
glowing objects: An electric hob glows dull red before it glows orange, while objects at room temperature look dark to the eye because their peak lies in the infrared.AQA
gold foil: The very thin material at which the alpha particles were fired in the experiment.AQA
good absorber is a good emitter: A surface that absorbs a given wavelength well also emits that wavelength well, at the same temperature.AQA
gradient: On a distance–time graph, found by taking two points on a straight section and dividing the change in distance by the change in time.AQA, OCR
gradient and resistance: At any given potential difference the component carrying the smaller current has the larger resistance and its line has the smaller gradient.AQA
gradient as acceleration: The gradient of a velocity-time line is the acceleration, found by reading a change in velocity with its matching change in time from a large triangle.AQA
gradient is g: The gradient of a weight against mass graph is the gravitational field strength.AQA
graph interpretation: Check the axis quantity and unit, read up from the speed to the curve and across, and compare different vehicles only at the same speed.AQA
Graphical representation of elastic behaviour: A force–extension graph plots as a straight line through the origin in the proportional region, and beyond the elastic limit the line curves.OCR
gravitational attraction: The pulling together of the particles of the cloud, which makes it collapse and become denser and hotter.AQA
Gravitational collapse: Gravity continuously pulls the star's mass inwards, attempting to collapse it, and the initial cloud of dust and gas collapses as gravity draws the matter…AQA
gravitational field: All matter has one, and it causes attraction between masses rather than pushing them apart.AQA, OCR
Gravitational field strength: Measured in newtons per kilogram, this term is included in the calculation so the result carries the correct units of pressure.AQA, OCR
Gravitational field strength g: The force per unit mass, with a value of 10 N/kg at the Earth's surface.OCR
gravitational force: The force that pulls a satellite towards the centre of its orbit, acting along the line joining the Earth and the satellite.AQA
Gravitational force towards the centre: The force on the planet acts towards the centre of its circular orbit and is always perpendicular to the planet's motion.OCR
Gravitational potential energy: The energy associated with an object raised above ground level, given by E_p = m × g × h, with g taken as 9.8 N/kg and h the height in metres.OCR
gravitational potential store: The energy associated with an object raised above ground level, calculated as Eₚ = m g h with g = 9.8 N/kg.AQA
Gravity: An interaction between masses, such as the Earth pulling a falling object downwards.OCR
gravity acting towards the centre: In a circular orbit gravity pulls the satellite towards the centre of the circle, at right angles to the way it is moving.AQA
Gravity and core heating: As the material falls inward, gravitational potential energy becomes thermal energy, so the core heats up.OCR
Gravity and free fall: Near the Earth's surface any object falling freely under gravity has an acceleration of about 9.8 m/s², directed towards the Earth's centre.AQA
Gravity as the force maintaining orbits: Gravity provides the centripetal force needed to keep the satellite in a stable orbit.OCR
greater red-shift: The greater increase in wavelength, shown by dark lines shifted further towards the red end.AQA
green and yellow earth: The earth wire is identified by green and yellow stripes on its insulation.AQA
Greenhouse effect and Earth's temperature: Greenhouse gases absorb and re-emit some of the Earth's outgoing longer-wavelength infrared, so the balance sets the surface temperature.OCR
greenhouse gases: Gases such as carbon dioxide and methane that absorb outgoing infrared and re-emit some of it downwards, cutting the rate of loss to space.AQA

H

Half-life: The time taken for the number of undecayed nuclei in a sample to halve, or for the count rate from the sample to fall to half its starting value.OCR
halving chains: Write the chain out in full, such as 800, 400, 200, 100, so the number of half-lives is on the page.AQA
halving the path: In an echo calculation, the total distance the sound covers is halved to find the distance to the reflecting surface.AQA
handling with tongs: Using long tongs to handle sources, holding them at arm's length and pointing them away from people.AQA
hanging rod demonstration: A charged polythene rod is brought near an identical charged rod hanging from a thread, and the hanging rod swings away.AQA
hazard over time: The half-life sets how the hazard is spread over time, so a short half-life source soon becomes safe while a long half-life material stays hazardous for…AQA
hazardous effects: Ultraviolet waves, X-rays and gamma rays carry enough energy to have hazardous effects on human body tissue.AQA
hearing loss with age: The range of human hearing narrows with age, with the top end falling first.AQA
heating: Calculated as E = m × c × Δθ, with mass in kilograms, specific heat capacity in J/(kg °C) and temperature change in °C.AQA, OCR
heating a system: Changes the energy stored within the system by increasing the energy of the particles that make up the system.AQA
heating and cooling graphs: Graphs that include changes of state, in which sloping parts belong to ΔE = m c Δθ and flat plateaus belong to E = m L.AQA
Heating and friction: A moving car transfers energy by friction and air resistance, warming the brakes, tyres and surrounding air.OCR
heating by absorbed light: Absorbed light is not destroyed; its energy is transferred to the internal energy store of the surface, so the surface becomes hotter.AQA
heating by infrared: Infrared from a grill is absorbed by food, raising its internal energy store and its temperature.AQA
heating calculations: Calculations using ΔE = m c Δθ to find the energy transferred when a system is changed by heating.AQA
heating curves: A graph whose sloping sections are temperature rises and whose flat sections at the melting point and the boiling point are changes of state.AQA
Heating effect on resistance: A larger current makes the filament hotter, which increases its resistance, so resistance rises as current rises.OCR
heating elements: A high resistance element through which the current passes, with collisions between the moving charges and the metal ions transferring energy to its thermal…AQA
heating graph sections: The sloping parts are governed by specific heat capacity and the flat parts by specific latent heat, where the temperature is constant.AQA
hertz: The unit in which frequency is measured, where 1 Hz means one wave per second.AQA, OCR
high potential difference: Transmitting at a high potential difference gives a smaller current for the same power, so less energy is dissipated to the surroundings.AQA
high specific heat capacity: A high value means the substance needs a lot of energy to warm up and also releases a lot as it cools.AQA
high temperature and pressure: Extremely high temperatures and pressures are needed to bring positively charged nuclei close enough to fuse.AQA
High-energy end of the electromagnetic spectrum: Ultraviolet, X-rays and gamma rays sit at the high-frequency, short-wavelength end, so each photon carries a relatively large amount of energy.OCR
High-voltage transmission advantages: Transmitting at high voltage means a low current, and since heating in cables depends on current, less energy is wasted.OCR
Higher Tier: The level at which the relationship is written as F = m Δv ÷ Δt.AQA
highly penetrating: Gamma rays are the most penetrating of the nuclear radiations, needing thick lead or metres of concrete to reduce them appreciably.AQA
Hooke's law proportionality: Up to a limit, doubling the force roughly doubles the extension, and you note where the spring stops obeying this pattern.OCR
horizontal and vertical: The two directions usually chosen for the components, with the force drawn as the diagonal of a rectangle whose sides run along them.AQA
hot dense beginning: The universe began from a very small region that was extremely hot and extremely dense.AQA
how fusion works: Two light nuclei are forced together into a single heavier nucleus, and the protons of both end up in the same nucleus.AQA
how science develops: Each stage waited on new experimental techniques and on evidence that the existing picture could not explain.AQA
how science works: A model makes a prediction, experiments test it, and other scientists check the work by peer review and by repeating the measurements themselves.AQA
Hydroelectricity: A resource in which falling water in a hydroelectric scheme spins turbines.OCR

I

I to V characteristics: What is investigated for a variety of circuit elements, including a filament lamp, a diode and a resistor at constant temperature.AQA
I² R heating: The power wasted heating the cables is P = I² R, which falls with the square of the current.AQA
I² R losses: The power wasted heating the cables depends on the square of the current, P = I² R.AQA
identical particles: The nucleus is built from identical positively charged particles, each particle having the same amount of positive charge.AQA
identifying a source: Using the fall of count-rate to background at a stated distance as evidence of the type of radiation emitted.AQA
identifying decay type: A rise of one in the proton number with no change in mass number is the signature that identifies a decay as beta.AQA
identifying elements: Two atoms are the same element only when their proton numbers, or equivalent atomic numbers, are compared and match.AQA
identifying the emitted particle: Running the same method backwards: if the atomic number rose by one and the mass number held still, the decay was beta.AQA
identity, charge and mass: A change in the lower number means a different element, a change in the upper number alone means a different isotope, and a charge means an ion.AQA
Improving reliability through repeats and means: Repeating readings where appropriate and calculating a mean to improve the reliability of the recorded data.OCR
increase in wavelength: The observed change in light from most distant galaxies, where the light arrives with a longer wavelength than the same light would have if the galaxy were at…AQA
increased atomic number: There is now one more proton, so the atomic number rises by one and the daughter is the next element along in the periodic table.AQA
increasing the current: One of the two changes that strengthens the field around a current carrying wire, the other being shaping the wire into a solenoid.AQA
independence from conditions: Heating, cooling, dissolving or squeezing the material all leave the decay untouched, so nothing done to the outside changes the rate.AQA
Independence of acceleration from mass: The mass cancels in a = W/m, so a heavy ball and a light ball accelerate at the same rate when air resistance is negligible.OCR
indirect evidence: Evidence about parts of the Earth which are not directly observable, so the evidence has to be indirect.AQA
indivisible atoms: Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.AQA
induced alternating current: The wave can induce oscillations in an electrical circuit, producing an alternating current in the aerial with exactly the same frequency as the radio wave…AQA
Induced current and its magnetic field: If the conductor forms part of a complete circuit, the induced potential difference drives a current that generates its own magnetic field.OCR
induced magnet: A material that becomes a magnet when it is placed in a magnetic field.AQA
induced magnetism: When a magnetic material is placed in a field, the domains inside it line up so that the pole induced nearest the magnet is always the opposite pole.AQA
induced magnets: These are magnetic only while in a field, their poles are set by that field, the force is always attraction, and magnetism is lost quickly once the field is…AQA, OCR
induced poles: An unmagnetised piece of iron in a magnetic field becomes an induced magnet with the opposite pole facing the magnet, and the induced poles turn round when…AQA
induced potential difference: What is produced when the field through the coil changes, lighting the lamp in a shake torch, and where the circuit is complete a current is induced.AQA
Induced potential difference from a changing magnetic field: A change in the magnetic field around a conductor gives rise to a potential difference across its ends.OCR
Induced potential difference from a changing magnetic flux: The alternating potential difference across the primary produces a changing magnetic flux in the iron core, and this induces an alternating potential…OCR
Induction of oscillations by radio waves: A radio wave arriving at a conductor can induce an oscillating current in that circuit, which is how a receiving aerial works.OCR
inelastic deformation: Once stretched far enough for this, some of the work done goes into permanently rearranging the material rather than into the elastic store, and the spring…AQA
inertia: The tendency of objects to continue in their state of rest or of uniform motion.AQA, OCR
Inertial mass: A measure of how difficult it is to change the velocity of an object, including speeding up, slowing down or changing direction.AQA, OCR
Inertial Mass (Higher Tier): The ratio of force to acceleration (m = F/a).OCR
infrared: Radiation given out by every warm object, which an infrared heater produces to warm you strongly without looking bright.AQA
infrared absorption: An object absorbs infrared radiation coming from its surroundings at the same time as it emits infrared radiation.AQA
infrared emission: All bodies, no matter what temperature, emit infrared radiation, and emission and absorption always happen together.AQA
infrared radiation: The radiation that a body radiates more of in a given time the hotter the body is.AQA
Initial velocity: The velocity u at the start of the motion, which together with acceleration a and time or displacement determines the value of the final velocity.AQA
injury risk: The chance of injury, which falls because the force on the person is smaller.AQA
instantaneous speed: The speed at one instant, found from the gradient of the tangent to the distance–time graph at that time.AQA
Insulation: Material used to reduce the rate of thermal energy transfer to the surroundings.AQA
Insulator: A material that does not allow electric charge (electrons) to flow through it easily.Pearson Edexcel
insulators: The materials must be insulators for the effect to show, because charge cannot move through an insulator and so stays where the rubbing put it.AQA
intensity against wavelength: A graph of this for a black body is a curve with a peak, and raising the temperature lifts the whole curve and grows the area beneath it.AQA
Intensity depends on temperature: The hotter the object, the greater the intensity of radiation it emits at every wavelength.OCR
interaction between pairs of objects: A situation in which forces arise between two objects, and each object in the pair experiences a force.OCR
interaction of two fields: A current carrying wire produces its own magnetic field, and when placed in the field of a magnet the two fields interact, reinforcing on one side of the wire…AQA
Interaction of waves with matter: At a boundary waves can reflect, refract or be absorbed, and in a fluid waves such as sound or water waves spread and can be reflected or refracted.OCR
Interaction Pair: A pair of forces that are equal in size, opposite in direction, of the same type, and act on two different interacting objects.AQA, OCR
interaction pairs: When two objects interact, each exerts a force on the other, and these forces are equal in magnitude, opposite in direction and of the same type.AQA
Internal dose: Dose from contamination that can be inhaled or swallowed and continues delivering dose until removed.OCR
internal energy: Energy stored inside a system by the particles that make up the system, being the total of the energy the particles have because they are moving and because…AQA
internal versus external hazard: Outside the body a gamma source is the greater hazard because the radiation reaches internal organs, while inside the body an alpha source is far worse.AQA
interpreting arrow sizes: Check each arrow for its direction, its wavelength label and its size, then total the energy in and the energy out.AQA
interpreting data: Reading the values from a table or graph and stating a conclusion supported by the data.AQA
Interpreting graph shape physically: Explaining what the curvature means physically rather than merely calling it 'not straight'.OCR
Interpreting V–I characteristics: For a fixed resistor doubling V doubles I, while a filament lamp or thermistor gives a V–I graph that curves rather than staying straight.OCR
inverse frequency and wavelength: Because v = f λ and v is fixed, the shorter the wavelength, the higher the frequency.AQA
inverse proportion: Halving the volume doubles the pressure, so pressure and volume are inversely proportional.AQA
Inverse relationship: For a fixed velocity, increasing frequency shortens wavelength and decreasing frequency lengthens it, because f and λ are inversely proportional when v is…AQA, OCR
Inverse relationship between orbital speed and radius: For a given central body, a faster stable orbit must have a smaller radius, and a slower stable orbit must have a larger radius.OCR
Inverse relationship between pressure and volume: If the volume is halved, the pressure doubles, because the same number of particles hits a smaller area more often.OCR
Inversely Proportional: A relationship between two variables where one increases as the other decreases, such that their product remains constant.AQA
Investigating fields with compasses and iron filings: Methods include plotting with a small plotting compass moved around the magnet, and sprinkling iron filings to reveal the pattern.OCR
ion vibration and collisions: The metal ions in the lattice vibrate more strongly at higher temperature, so the electrons carrying the current collide with them more often and find it…AQA
Ionisation: If the radiation absorbed is energetic enough, such as ultraviolet or an X-ray, the electron is removed from the atom completely and the atom becomes a…AQA, OCR
Ionisation (Higher Tier): The process by which a neutral atom or molecule gains or loses electrons to become a charged ion.Pearson Edexcel
Ionisation and cell damage: Energy can be transferred to atoms and molecules in living tissue, ionising them or breaking chemical bonds.OCR
ionisation of electrons: Radiation passing through matter ionises atoms by knocking electrons out of them.AQA
ionising: A property of X-rays and gamma rays, which can penetrate deep into the body to cause gene mutations and cancer.AQA
ionising power: Runs alpha, then beta, then gamma, because an alpha particle is large and doubly charged and rips electrons from atoms quickly.AQA, OCR
ionising radiation: X-rays and gamma rays are highly penetrating and are classified as ionising radiation, carrying enough energy to knock electrons off atoms.AQA
ions: Any charge written after the symbol refers to electrons, not protons, so an ion has lost or gained electrons while the two nuclear numbers stay the same.AQA
iron as the limit: Fusing nuclei heavier than iron takes energy in rather than giving it out, so no star can make elements such as gold or uranium in its core.AQA
iron core: Iron is used for the core because it is easily magnetised and demagnetised, allowing its magnetism to follow an alternating magnetic field.AQA
Iron core and electromagnets: Adding an iron core magnetises the iron and strengthens the field further, making an electromagnet.OCR
irradiation: Exposure to radiation from a source outside the object, where the source stays where it is and only the radiation reaches the object.AQA, OCR
Irradiation hazard: Dose delivered only while exposure lasts, so distance, shielding and limiting time reduce it.OCR
irradiation leaves nuclei unchanged: Radiation passing through matter ionises atoms by knocking electrons out of them, but it leaves the nuclei unchanged, so the object does not become radioactive.AQA
isotopes: Variants of an element with different neutron counts, while atoms of one element always share the same proton number.AQA, OCR

J

J/kg °C: The unit of specific heat capacity, carrying the whole definition: joules, per kilogram, per degree Celsius.AQA
joule: The unit produced when force is multiplied by distance, so a work done in newton-metres simply changes its label to this.AQA
joule and newton-metre: One joule and one newton-metre are the same amount of energy, because multiplying newtons by metres is exactly what the work equation does.AQA
Joulemeter: A device used to measure the electrical energy transferred to an appliance.AQA
joules: The unit of work done, where one joule is done when a force of one newton causes a displacement of one metre.AQA
joules per coulomb: The energy transferred per coulomb, so a 1 V potential difference means 1 joule is transferred for every coulomb that passes.AQA
Judging suitability from observations: Asking whether the apparatus can detect the wave, resolve the effect and give repeatable readings.OCR
Judging suitability of measurements: Deciding whether apparatus gives a clear, repeatable reading at the scale of the observed wave, not merely that it is available.OCR
Junction: A point in a circuit where three or more conductors meet, allowing current to split or recombine.OCR
junctions: A junction is the point at which the wire splits and a parallel branch begins.AQA

K

kilogram: The coherent SI unit of mass, required so that force comes out in newtons when acceleration is in m/s².AQA
kilowatt-hours: Used for home appliances, where 1 kW h = 1000 W × 3600 s = 3 600 000 J.OCR
Kinetic energy: The energy associated with a moving body, given by E_k = ½ × m × v², with mass in kilograms and speed in metres per second, giving joules.AQA, OCR
Kinetic energy and temperature: Heating the gas transfers energy to the particles, so their mean kinetic energy rises and they move faster; cooling reverses this.OCR
kinetic energy of fragments: The two fragments and the two or three neutrons are thrown out at speed, so all fission products have kinetic energy, which holds most of the energy released.AQA
kinetic energy of particles: Increases while the temperature is rising, so the particles vibrate or move faster and their mean kinetic energy increases.AQA
kinetic energy store: The store from which energy is transferred out when the brakes are applied, so that the vehicle slows.AQA
Kinetic model of a gas: Gas particles move randomly at high speed, and raising the temperature increases their average kinetic energy so they move faster.OCR
kinetic store: The energy associated with a moving object, calculated as Eₖ = ½ m v², so doubling the speed quadruples the energy.AQA
Kinetic Theory of Gases: A model that explains the properties of gases by describing the behaviour of their particles: gas particles are in constant, random motion with a range of…AQA

L

labelling: Marking the neutrons and the nuclei so the two can be told apart, since an examiner cannot credit an unlabelled circle.AQA
large triangle: A triangle used to take the gradient, with both readings exact from grid intersections, such as a velocity rising from 4 m/s to 20 m/s over 8.0 s.AQA
latent heat: What melting or boiling needs instead of the equation, which applies only while the substance stays in one state.AQA, OCR
Latent heat of fusion: The specific latent heat used for melting or freezing.OCR
Latent heat of vaporisation: The specific latent heat used for boiling or condensing.OCR
Law of conservation of momentum: The total momentum of the interacting objects before a collision equals the total momentum after it, provided no external resultant force acts on the system.OCR
law of reflection: The rule that the angle of incidence equals the angle of reflection, both measured from the normal.AQA
lead-lined storage: Returning the source to its lead-lined box between measurements rather than leaving it out.AQA
LEDs: Light emitting diodes, which behave the same way as diodes and emit light only when connected the right way round.AQA
length in the field: The length of the conductor that is inside the field, one of the three things the size of the force depends on.AQA
length represents magnitude: The length of the arrow stands for the magnitude of the vector quantity, measured with a ruler against a stated scale.AQA
Leslie cube: A metal cube with four faces, matt black, shiny black, matt white and shiny silver, filled with hot water.AQA
Lever: A lever balances when the moment of the effort equals the moment of the load about the pivot, so a small effort far from the pivot balances a large load close…OCR
levers: A rigid bar turning about a pivot, where a small effort a long way from the pivot balances a large load close to it.AQA
light dependent resistors: A component that responds to light rather than heat, with resistance that is very high in darkness and can fall to a few hundred in bright light.AQA
light gates: Apparatus placed at two points that gives the speed at each point, so the change in speed divided by the time between the gates gives acceleration or…AQA, OCR
light intensity: The brightness of the light falling on an LDR; as it increases, the resistance of the LDR decreases.AQA
Light nuclei joining: Two light nuclei join to form a single heavier nucleus, as in a multiple-choice option that names this process.OCR
Light-dependent and thermistor sensing: An NTC thermistor drops in resistance as temperature rises, and an LDR drops in resistance as light intensity rises.OCR
like and unlike poles: Like poles repel and unlike poles attract, and the force grows as the magnets get closer.AQA
like charges repel: Two objects that carry the same type of charge push apart, because each sits in the electric field of the other and is pushed outwards.AQA
like poles repel: Two north poles pushed together repel, and so do two south poles.AQA
limit of proportionality: The point up to which the extension is directly proportional to the force applied; past it the line bends away from the straight part.AQA
limited frequency range: The conversion of sound waves to vibrations of solids works only over a band of driving frequencies.AQA
Limited range of human vision: Our eyes can only detect a limited range of the electromagnetic spectrum, responding to only a small slice of it.OCR
limits of science: Science has the ability to identify environmental issues arising from the use of energy resources but not always the power to deal with the issues.AQA
line of action: The line along which a force acts; if it passes through the pivot, the force causes no rotation.AQA
Line of action of a force: The distance must be measured in the same direction as the force, and a force at right angles to the motion does no work because there is no movement along it.OCR
linear: A straight line through the origin on a current against potential difference graph, meaning an ohmic element whose resistance is constant.AQA
Linear element: Gives a straight line through the origin on a potential difference–current graph, so its resistance stays constant as current changes.OCR
linear scale: Because the extension is directly proportional to the force applied, the scale has evenly spaced divisions.AQA
Linear spring behaviour: The graph is a straight line from the origin, so the area is a triangle and the work done is W = ½Fx.OCR
Linear versus non-linear graphs: A linear relationship gives a straight-line graph through the origin, while a non-linear relationship gives a curved graph.OCR
lines never cross: Magnetic field lines never cross and never stop in mid air, and they are closest together at the poles.AQA
liquid outer core: S-waves cannot travel through it, unlike P-waves, which provides crucial evidence for the Earth's internal liquid structure.AQA
liquids and gases: Both can be pumped along a pipe and both press outwards on every surface they touch.AQA
little absorption: Very little of the incident light is taken in, which is why white surfaces warm up slowly.AQA
live at 230 V: The potential difference between the live wire and earth is about 230 V.AQA
live neutral earth: The three cores of a mains cable; live and neutral carry the working current, and the earth core is a safety connection to the metal case.AQA
live to earth connection: Any accidental connection between live and earth completes a path that puts the full 230 V across your body and charge passes through you.AQA
Live wire: Carries the alternating potential difference from the supply and alternates between a positive and a negative potential difference relative to the neutral wire.AQA, OCR
Live-to-earth faults and shock: Touching the live wire, or a fault linking it to an earthed case, completes a path to earth so a large current can flow through a person, causing a shock.OCR
Long half-life: Activity falls slowly, so the material remains hazardous for a long time and persists in the environment.OCR
long to short wavelength: Because the speed is the same for all of them, going from long to short wavelength is also going from low to high frequency.AQA
longitudinal: Describes a wave in which the molecules oscillate backwards and forwards along the direction the sound travels.AQA
longitudinal motion: The rock particles oscillate backwards and forwards parallel to the direction of energy transfer.AQA
longitudinal wave: A wave in which the oscillations or vibrations are parallel to the direction of energy transfer.AQA
longitudinal waves: Waves such as sound in air, where air particles vibrate back and forth along the direction the sound travels, forming compressions and rarefactions.AQA, OCR
loss of electrons: Negatively charged electrons are transferred away from the object, which leaves its protons outnumbering its remaining electrons.AQA
loss of energy: The nucleus was left in an excited, higher-energy arrangement and emitting the gamma ray carries that surplus energy away, leaving the nucleus more stable.AQA
loss of induced magnetism: An induced magnet loses most or all of its magnetism quickly when removed from the magnetic field.AQA
Loudspeaker: A device in which a vibrating cone in a solid structure pushes air to create sound waves.OCR
low resistance path: The earth path has very low resistance, so the resulting current is large, far larger than the appliance's normal current, and the fuse melts quickly.AQA
Lubrication: Oil or grease between moving parts reduces friction, so less energy is transferred by heating to the parts and surroundings.AQA, OCR

M

magnetic compass: Contains a small bar magnet balanced on a pivot so that it can turn freely.AQA
magnetic effect of a current: A current-carrying wire is surrounded by a magnetic field, shown by a plotting compass deflecting or iron filings forming concentric circles.AQA, OCR
magnetic field: The region around a magnet where a force acts on another magnet or on a magnetic material.AQA
Magnetic field around a current: A current-carrying conductor produces a magnetic field around itself, and this field interacts with the field of a nearby magnet.OCR
Magnetic field direction: By convention the lines run from the north pole round to the south pole outside the magnet, and the arrow gives the force direction on a north pole placed at…OCR
Magnetic field patterns: Field lines leave a north pole and enter a south pole and never cross, and the closer the lines the stronger the field.OCR
magnetic flux density: B in the equation, measured in tesla (T), and found by dividing the force by the product of current and length.AQA, OCR
Magnetic Flux Density (B): A measure of the strength of a magnetic field at a given point, defined as the force per unit current per unit length on a conductor perpendicular to the field.Pearson Edexcel
Magnetic flux density and field direction: The first finger points along the magnetic field, from north to south pole.OCR
magnetic flux density in tesla: A quantity in tesla that is multiplied by current in amperes and length in metres to give the force in newtons.AQA, OCR
magnetic force: Acts between magnetic poles and between a magnet and a magnetic material, with unlike poles attracting and like poles repelling.AQA
magnetic linking: The core links the two coils magnetically, so the changing field through the secondary induces an alternating potential difference across it.AQA
magnetic materials: Iron, steel, cobalt and nickel are the materials that become magnets when placed in a magnetic field.AQA
Magnetic poles: A permanent magnet has two poles, north and south, and the rule is that unlike poles attract and like poles repel.OCR
magnification ratio: A ratio of two lengths, image height divided by object height, which has no unit.AQA
magnifying glass: The arrangement in which the object is closer to the lens than the principal focus, giving a virtual image that is upright and enlarged.AQA
Magnitude: The size or numerical value of a quantity (e.g., the size of a force in Newtons).AQA
magnitude and direction: A displacement is expressed in terms of both of these, and a magnitude on its own always loses the direction mark.AQA
magnitude only: Having a number and a unit with no direction attached, which is how a scalar quantity is completely described.AQA
main sequence: One of the stages that every star passes through before the two routes separate.AQA
mains frequency 50 Hz: The supply completes 50 full cycles every second, so one cycle lasts 1 ÷ 50 = 0.02 s.AQA
man-made sources: Sources such as the fallout from nuclear weapons testing and nuclear accidents that contribute to background radiation.AQA
Mass: Measured in kilograms (kg) with the symbol m, it is the quantity of matter in an object and resists a change in motion.AQA, OCR
mass and stiffness: Properties of a solid part such as the ear drum that set its working range.AQA
mass and temperature rise: For the same energy input, a larger mass of the same substance gives a smaller temperature rise.AQA
mass converted into energy: Each of these reactions releases energy, because some of the mass of the nuclei is converted into energy.AQA
mass converted to energy: In fusion, some of the mass may be converted into the energy of radiation.AQA
mass decides the route: The mass of the star decides which route it takes after the main sequence.AQA
mass number: The number written above the chemical symbol in a nuclide symbol, which differs between isotopes of an element.AQA
mass unchanged: The quantity of matter in an object, which is the same everywhere and stays the same wherever the object is.AQA
Mass versus weight: Mass in kilograms measures how much matter is present, while weight is the gravitational force on that mass in newtons.OCR
Mass-energy conversion: The total mass of the product nucleus is slightly less than the combined mass of the original nuclei, and the missing mass appears as energy of radiation.OCR
massive object: One that produces a stronger gravitational field than a less massive object does.OCR
matched comparison: The comparison is written in matched pairs, such as in the convex lens the rays converge, whereas in the concave lens they diverge.AQA
Matching apparatus to the quantity measured: Picking apparatus that measures each quantity to a sensible precision, such as a balance for mass, a measuring cylinder for volume and a thermometer for…OCR
Matching distance and time measurements to the same motion: Marking clear start and finish points so that the distance measured matches the time measured.OCR
matching frequencies: The frequency of the radio wave produced is the same as the frequency of the alternating current driving the aerial.AQA
matching frequency: The current has exactly the same frequency as the radio wave, so the information carried by the wave survives the transfer.AQA
material choice: Water is used in heating systems and engine coolants, and reactor walls are chosen for a very high specific heat capacity so an enormous energy transfer…AQA
material interfaces: The boundaries between materials where reflection, transmission and absorption of waves take place.AQA
matt and shiny surfaces: Matt surfaces absorb more infrared than shiny surfaces of the same colour, as shown by the temperature rises of the cubes.AQA
matt black best emitter: The matt black face gives the highest reading, showing that a matt black surface is the best emitter of infrared.AQA
maximum speed: The speed at which the resistive forces have grown until they equal the driving force, so the speed stays constant.AQA
mean kinetic energy: The average kinetic energy of the molecules, which rises when the temperature is raised and falls when the gas is cooled.AQA
mean of intervals: Find the time interval over which the count rate falls to half, do it again for a second interval and take the mean.AQA
Measurement of energy transfer: Recording readings with correct units, distinguishing energy in joules from work done in joules and from temperature change in degrees Celsius.OCR
measurement technique: Zero the instrument first, hang it vertically, let the object come to rest and read the scale at eye level.AQA
measuring distance: Comparing how bright a supernova looks with how bright it really is gives its distance, measured independently of its red-shift.AQA
Measuring force and extension: Calculating the force from the weight of each mass using W = m × g, and finding the extension by subtracting the original length from the new length.OCR
measuring instruments: Appropriate apparatus such as a ruler, micrometer or Vernier callipers for measuring dimensions, and a balance for measuring mass.AQA
Measuring length and calculating area: Measuring length with a metre rule or vernier callipers, then finding area by multiplying two perpendicular lengths and giving the unit in m².OCR
measuring many waves: Measuring across ten complete waves with a millimetre rule and dividing the total by ten, because measuring one wave alone gives a large percentage uncertainty.AQA
Measuring volume of a regular solid: Measure length, width and height with a ruler and multiply them to get volume in cm³.OCR
measuring wavelength and frequency: Measuring across ten wavelengths with a rule and dividing by ten, and reading the frequency from the signal generator or counting ripples passing a mark over…AQA
medical tracers: A gamma-emitting isotope is taken into the body and followed by a detector outside it, building an image of how an organ is working.AQA
Medical uses of nuclear radiation: Nuclear radiations are used in medicine for exploration of internal organs and for control or destruction of unwanted tissue.OCR
medium required: Because it needs particles, sound cannot cross a vacuum, unlike light.AQA
meltdown: The same runaway behaviour in a power station, where the fuel is not suitable for a bomb-type explosion, showing itself as the core overheating and damaging…AQA
Meniscus: The point at which a measuring cylinder is read for volume, in cm³ or ml.OCR
metal case: The part of an appliance joined to the ground by the earth wire, which would otherwise rise to about 230 V if the live wire touched it.AQA
meters: A voltmeter is a circle marked V and an ammeter is a circle marked A.AQA
Metres: The unit in which distance travelled is measured, written as m.AQA, OCR
Microphone: A device in which sound waves vibrate a diaphragm and the movement is converted into an electrical signal.OCR
Milky Way: The galaxy that contains our solar system, seen from the inside as a faint band of light in a dark sky.AQA
milli prefix: The ordinary prefix used here, the same prefix logic already used for millimetres and milliamps, applied unchanged.AQA
moderator and coolant: Neutrons collide with atoms in the moderator to slow down, and energy is transferred to the coolant, which is pumped to a heat exchanger to boil water.AQA
molecular collisions: Air molecules bouncing off any surface they meet, each one exerting a tiny force on that surface.AQA
molecule number: The count of air molecules above a surface, which decreases as the height of the surface above ground level increases.AQA
Moment: A force applied at a distance from a pivot produces a turning effect equal to force multiplied by the perpendicular distance from the pivot.OCR
Moment as the turning effect of a force: A moment measures the turning effect of a force about a pivot.OCR
moment of a force: The turning effect of a force, defined by the equation moment of a force = force × distance.AQA
moments are not energy: A moment is a turning effect measured in newton-metres, not an energy, so it is never rewritten in joules.AQA
Momentum: A vector quantity that measures how hard it is to stop a moving object, calculated as mass in kilograms multiplied by velocity in metres per second.AQA, OCR
momentum calculations: Calculations involving an event such as the collision of two objects, using total momentum before = total momentum after with each momentum as mass × velocity.AQA
moons: Natural bodies that orbit planets, are held in orbit by gravity and are seen only by reflected sunlight.AQA
motor appliances: Appliances in which a current in a coil sitting in a magnetic field makes the coil turn, so energy is transferred electrically to the kinetic store of the…AQA
motor effect: The conductor's field interacts with the magnet's field to produce a force on the conductor, and this is exploited in loudspeakers and electric motors.AQA, OCR, Pearson Edexcel
Movement of particles in each state: Solid particles vibrate about fixed positions, liquid particles can slide past one another, and gas particles move randomly at high speed.OCR
moving-coil loudspeaker: A device in which a coil sits in the narrow gap between the poles of a cylindrical magnet, fixed to the narrow end of a paper cone held at its rim by a…AQA
moving-coil microphone: A device in which sound waves cause a diaphragm to vibrate, making an attached coil cut the magnetic field lines of a fixed magnet and inducing a potential…AQA
multi-stage journeys: Journeys shown by joining points with distinct straight line segments for periods of constant speed, rather than a single line of best fit.AQA
mutually perpendicular directions: The thumb, first finger and second finger of the left hand are held mutually at right angles.AQA

N

named stores: The answer has to name the store the energy is transferred from and the store the energy is transferred to.AQA
national grid: The network of cables and transformers that carries electrical power from power stations to homes and businesses.OCR
National Grid transmission: Step-up transformers increase potential difference and decrease current, and since energy wasted heating cables depends on the square of the current, a…AQA
natural frequency or resonant range: A detector, a vibrating structure or a medium responds strongly near this range but weakly far from it.OCR
natural satellites: Objects that were not put in orbit by people, such as the moons that orbit planets.AQA
Natural satellites (moons): Most planets have moons that orbit them, for example the Moon orbiting Earth.OCR
natural sources: Sources such as rocks and cosmic rays from space that contribute to background radiation.AQA
Nature of light: Light is an electromagnetic wave, produced by oscillating electric and magnetic fields that travel together through space.OCR
nebula: A cloud of dust and gas, mostly hydrogen, from which the Sun was formed.AQA
Negative acceleration: Indicates a velocity change in the negative direction, meaning speeding up if velocity is negative, or slowing down if positive.AQA
negative charge: An object is negatively charged when it holds more electrons than protons, so more negative than positive charge.AQA
negative gradient: A line sloping downwards means the object is slowing, and the gradient comes out negative.AQA
nerve impulses: Electrical impulses sent along the auditory nerve by hair cells in the cochlea, which the brain interprets as sound.AQA
Net (resultant) force: Found by adding parallel vectors tip to tail and combining perpendicular ones with a right-angled triangle, then measuring with a ruler and protractor.OCR
net absorption: The overall transfer of energy into a body when it absorbs radiation faster than it emits radiation.AQA
net decline as a ratio: The fall in a radioactive emission after a given number of half-lives, written as a ratio such as 1:16 after four half-lives.AQA
Net force perpendicular to a surface: The combined effect of many collisions is a net force acting at right angles to the surface.OCR
Net resistance: In series it equals the sum and is larger than either resistor; in parallel it is smaller than the smallest branch resistance.OCR
Net upward force on a submerged surface: The pressure on the lower surface exceeds the pressure on the upper surface, so the liquid pushes up more strongly than it pushes down.OCR
neutral atoms: Atoms that have as many electrons as protons, so the atomic number also gives the electron count, although not for an ion.AQA
Neutral bodies and cancellation of charge: A body with equal numbers of positive and negative charges has zero net charge, because the charges cancel when equal in number.OCR
neutral near earth potential: The neutral wire is at, or close to, earth potential, which is 0 V.AQA
neutral object: An object that holds as many electrons as protons, so the charges cancel.AQA
neutral point: A point on the line between the magnets where the two fields are equal and opposite and cancel.AQA
neutral wire: Completes the circuit and is held at about zero potential difference, close to earth potential.AQA, OCR
neutron absorbed by second nucleus: At least one fission neutron is shown being absorbed by an additional large nucleus and causing fission.AQA
neutron absorption: The process by which control rods take in surplus neutrons; lowering the rods further into the core increases the number absorbed.AQA, OCR
neutron emission: Removing one neutron lowers the mass number by 1 while the proton number is unchanged, so charge stays the same.AQA, OCR
neutron losses: Neutrons that do not cause fission because many escape through the surface of the fuel or some are absorbed without causing fission.AQA
Neutron number: Found by subtracting the proton number from the mass number, and can differ between atoms of the same element.OCR
Neutron number from A − Z: The neutron number is found by subtracting the atomic number from the mass number.OCR
neutron star or black hole: The supernova leaves behind a neutron star or a black hole as the final stage.AQA
Neutrons and mass: Neutrons are neutral and contribute mass but no charge, so changing the neutron count leaves the nuclear charge unchanged.OCR
neutrons released: Two or three of these particles are released when a large unstable nucleus splits.AQA
newton: The SI unit of force; one newton gives a 1 kg mass an acceleration of 1 m/s².AQA
newton-metres: The unit of a moment of a force, written Nm.AQA
Newton's first law: An object keeps a constant velocity unless a resultant force acts on it.OCR
Newton's second law: A resultant force on a mass produces acceleration in the direction of that force, and acceleration is directly proportional to resultant force for a fixed…AQA, OCR
Newton's third law: When body A exerts a force on body B, body B exerts an equal-sized force on A in the opposite direction.AQA, OCR
newtonmeter: The instrument used to measure weight, hanging the object from the hook so the spring stretches and the scale reads the force.AQA, OCR
no centre to the expansion: The same pattern of galaxies receding would be seen from any galaxy, so the Earth is not at the centre.AQA
no change in nucleon number: Nothing but energy leaves the nucleus, so the mass number and the atomic number do not change.AQA
no change of charge: The atomic number, and so the charge, is unchanged because a gamma ray has no charge.AQA
no change of mass number: The mass number stays the same because a gamma ray has no mass and no nucleons are lost.AQA
no current in normal use: In normal operation there is no potential difference along the earth wire, so no current flows in it and the working current goes out along live and back…AQA
no isolated poles: You cannot get a single pole on its own, because snapping a bar magnet in half simply gives two shorter magnets, each with a north and a south.AQA
no nucleus: There is no nucleus and no empty space, as matter and charge fill the atom uniformly.AQA
no reflection: A black body reflects none of the incident radiation, and it is the absence of reflection that makes a cold black body look black.AQA
no transmission: A black body transmits none of the incident radiation that reaches it.AQA
no unit for magnification: The final value has a unit for a height and no unit for a magnification, so the answer is left as a bare number.AQA
non-contact force: A force that acts between two objects that are not touching.AQA, OCR
non-contact forces: Forces where the objects need not touch, because the force acts through a field, as with magnetic attraction and repulsion between two magnetic poles.AQA
Non-contact forces of attraction and repulsion: Charged objects exert forces on each other without touching: like charges repel and opposite charges attract.OCR
non-contact interaction: The first object sets up the field, and the second responds to the field where it sits, so a force acts across a gap between two objects.AQA
non-destructive testing: An industrial use of ultrasound that finds cracks, voids and corrosion inside castings, welds and pipes without cutting them open.AQA
Non-equilibrium motion from unbalanced forces: In a non-equilibrium case such as a rocket accelerating, the exhaust pushes the rocket forward while the rocket pushes the exhaust backward with an equal force.OCR
non-ionising: A property of ultrasound meaning it will not mutate genes, which is why it is chosen over X-rays for a foetus.AQA
non-linear: Anything on a current against potential difference graph that is not a straight line through the origin.AQA
Non-linear element: Gives a curve on the graph, so its resistance changes with current.OCR
non-linear response: The way an LDR's resistance changes over several orders of magnitude, so its resistance against light intensity graph is a curve rather than a straight line.AQA
non-magnetic metals: Metals such as aluminium and copper feel no force at all from a magnet, neither attraction nor repulsion.AQA
non-ohmic components: Components such as lamps, diodes, thermistors and LDRs whose resistance is not constant but changes with the current through the component.AQA, OCR
non-renewable: Describes fossil fuels and nuclear fuel, which are finite rather than replenished as they are used.AQA
Non-renewable fuels: Fossil fuels and nuclear fuel, which are non-renewable because their supplies are finite.OCR
Non-SI to SI conversion factors: Factors used to convert non-SI units to SI before substituting, such as 1 km = 1000 m and 1 minute = 60 s.OCR
Non-uniform motion: Motion where the speed changes during a journey, so a single instantaneous speed does not describe the whole trip.OCR
Normal (perpendicular) force component: The force acting perpendicular to the surface; only this component counts, so a force acting along the surface contributes nothing to pressure.OCR
normal at 90°: A dashed line drawn at the point where the incident ray strikes the mirror, at 90° to the mirror surface.AQA
normal at each face: A dashed line drawn at 90° to the boundary at the point where the ray meets it, needed at both faces.AQA
normal contact force: The push of a surface on an object resting against it, acting at right angles to that surface.AQA, OCR
Normal force: The force created when particles in a fluid collide with a surface, acting at right angles to it.AQA
normal line: The construction line drawn at 90° to the surface at the point where the ray strikes.AQA
north to south outside: Outside a magnet, field lines run from the north seeking pole round to the south seeking pole, and the arrows go that way.AQA
not a chemical reaction: The energy comes from the nucleus rather than from a chemical reaction, so it is not supplied by burning the uranium.AQA
nuclear changes: Changes inside the nucleus produce gamma rays, which sit at the highest frequency end.AQA
Nuclear charge: The nucleus carries a positive charge because of its protons, and neutrons add mass but no charge.OCR
Nuclear charge and isotope identity: Nuclear charge equals +Z elementary charges, so isotopes of one element share the same charge, and Z fixes the element so identity is unchanged.OCR
Nuclear composition: Atomic nuclei are composed of both protons and neutrons, which are the particles that make up an atomic nucleus.OCR
Nuclear decay equations: The parent nuclide is written on the left and the daughter nuclide plus the emitted particle on the right, with both totals checked before choosing an answer.OCR
nuclear equations: Used to represent radioactive decay, showing what a nucleus turns into when it decays.AQA
nuclear explosion: The explosion of a nuclear weapon, caused by an uncontrolled chain reaction releasing all the energy at once.AQA
nuclear fission: The splitting of a large and unstable nucleus into two smaller nuclei that are roughly equal in size.AQA, OCR
nuclear fuel: A finite, non-renewable resource that gives reliable electricity on demand and releases no carbon dioxide but leaves radioactive waste.AQA
nuclear fusion: Lighter nuclei join to form heavier nuclei, releasing energy because some of the mass of the nuclei is converted into energy.AQA, OCR
Nuclear instability: Some nuclei have too much energy or an unsuitable balance of protons and neutrons, so they are unstable and may emit radiation.OCR
Nuclear mass: Differs between atoms of the same element because neutrons carry mass, while the proton number stays the same.OCR
nuclear not chemical: The change is to the nucleus, not to the electrons, so it is nothing like burning and releases far more energy per atom than any chemical reaction.AQA
Nuclear notation with mass and proton numbers: Writing a nucleus with its mass number as a superscript and its proton number as a subscript, for example uranium-238 as ²³⁸₉₂U.OCR
nuclear origin: Gamma rays originate from changes in the nucleus of an atom, not from the electrons.AQA
nuclear radius: The radius of a nucleus is less than 1/10 000 of the radius of an atom.AQA
nuclear store: The store of the fuel from which every fission event transfers energy, rather than energy being created.AQA
nucleon number: Another word for the mass number, meaning the same thing if a question uses that word.AQA
nucleus: The positively charged central part of an atom, composed of both protons and neutrons.AQA
nuclide notation: A representation carrying the chemical symbol, the mass number above it and the atomic number below it.AQA
nuclide symbols: A representation read as three separate questions, where the lower number names the element and the upper number gives protons plus neutrons.AQA
number of half-lives: Found by halving repeatedly or by writing the fall as a power of two.AQA
number of turns: Winding more turns onto the coil means each field line is cut once per turn, so the induced potential difference rises again.AQA

O

object distance: How far the object is from the lens, which decides whether the image is real or virtual.AQA
Observation and recording skills: Recording clear descriptions of what is seen, such as light passing through or a shadow forming, rather than conclusions.OCR
Observing waves in fluids: Watching waves travelling through a fluid, such as water in a ripple tank, and noting what can actually be seen or detected.OCR
Observing waves in solids: Watching waves travelling through a solid, such as a stretched string or a metal rod, and noting what can actually be seen or detected.OCR
occupational dose: Some jobs put people near sources, so workers such as radiographers, nuclear power station staff and aircrew receive a raised dose.AQA
Ohmic and non-ohmic behaviour: A fixed resistor keeps the same R whatever current flows, but a filament lamp or thermistor has a resistance that changes as current changes.OCR
ohmic conductor: A conductor where, at constant temperature, the current is directly proportional to the potential difference.AQA
opaque objects: Objects through which no light passes, so everything seen from them has bounced off their surface.AQA
opaque surfaces: For an opaque object the incident light has only two possible fates: it is reflected or it is absorbed, because none is transmitted through.AQA
open and closed containers: In an open container steam leaves the balance rather than vanishing, while in a sealed container the reading does not change at all.AQA
open switch still live: Opening a switch only breaks the loop, so the length of live wire between the consumer unit and the switch is still at about 230 V relative to earth.AQA
Opposing forces at different points: Forces must act in opposing directions at different points so that the object is pulled or pushed from more than one side, and are not balanced overall in the…OCR
opposing the change: An induced current generates a magnetic field that opposes the original change, either the movement of the conductor or the change in magnetic field.AQA
Opposing the original change: The direction of the induced current's magnetic field opposes the original change, in line with Lenz's law.OCR
opposite pole induced: A north pole induces a south pole facing it, so the two are pulled together.AQA
opposition and braking: The opposition rule doing useful work, where induced currents produce fields that oppose the motion and slow the car, as in a roller coaster brake.AQA
optical density: The more optically dense the material, the slower the wave goes in it.AQA
orbiting a planet: Going round a planet, which is what a moon does.AQA
orbiting the Sun: Everything else in the solar system orbits the Sun either directly or indirectly, and the Sun holds the whole system together by gravitational attraction.AQA
Order of magnitude: The nearest power of ten, used to describe a typical size rather than an exact figure.OCR
Order of the electromagnetic groupings: The groupings, in order of decreasing wavelength and increasing frequency, are radio, microwave, infrared, visible, ultraviolet, X-rays and gamma rays.OCR
order of the spectrum: Going from long to short wavelength, the groups are radio, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays.AQA
Order-of-magnitude estimation: Values far above 10 m/s² for ordinary road travel are unrealistic, while gentle public transport is near or below 1 m/s².OCR
Ordering the EM spectrum: Ordering the spectrum by increasing frequency gives decreasing wavelength.OCR
orders of magnitude: The two orders of magnitude to learn are 10⁻¹⁰ m and 10⁻¹⁴ m.AQA
Orientation of conductor to the field: The force is greatest when the conductor is at right angles to the field and zero when the conductor is parallel to the field.OCR
origin of gas pressure: Pressure comes from collisions: molecules strike the walls of the container and rebound, and the total force from all those impacts, divided by the wall area,…AQA
oscillating charges: Charges that move backwards and forwards, and whose acceleration produces a changing electric and magnetic field that travels away as an electromagnetic wave.AQA
oscillation about a fixed position: In both cases the particles oscillate about a fixed position, and only energy moves forward.AQA
Oscillation of particles about fixed positions: Each molecule oscillates about a fixed position and passes the disturbance to its neighbour, so a compression travels through the air while the air itself is…OCR
oscilloscope trace: For a dc supply it is a horizontal line displaced from the zero line, while for ac it is a wave spending equal time above and below zero.AQA
ossicles: Three small bones joined to the drum which pass the vibration on and amplify it before it reaches the fluid filled cochlea.AQA
outer electrons: The electrons held least tightly, so they are the ones that can be pulled away by rubbing two surfaces together or by ionising radiation.AQA
output against time graphs: Graphs of the potential difference generated in the coil plotted against time, which students should be able to draw and interpret.AQA
Overheating and fire risk: A direct connection between the live wire and earth also risks a large current, overheating and fire.OCR
own magnetic field: The field a permanent magnet produces all the time, present whether or not another magnet is nearby.AQA

P

P = I² R: Power equals current squared multiplied by resistance, used when you are given current and resistance.AQA
p = m v: The equation for momentum, in which p is momentum, m is mass in kilograms and v is velocity in metres per second.AQA
P = V I: Power equals potential difference multiplied by current, used when you are given potential difference and current.AQA, OCR
P-wave shadow zone: A band of the globe, roughly 105° to 140° away from the earthquake, where no direct P-waves arrive.AQA
paired forces: The two forces in an interaction, which are equal in size and opposite in direction.OCR
pairs of forces: To change the shape of a stationary object, more than one force has to be applied, such as the weight and the pull of the support on a hanging spring.AQA
parallax error: Reading the position of the bottom of the spring at eye level avoids this error when the millimetre rule is held vertically alongside.AQA
parallel branches: Components are in parallel when they sit on separate branches between the same two junctions, so charge divides and each branch is a complete path on its own.AQA
parallel circuit: A circuit in which the potential difference across each branch equals the supply value, the branch currents add to give the total current, and the combined…AQA, OCR
parallel emergent ray: The ray leaving the glass, which speeds up and bends away from the normal by the same amount, so for a rectangular block it is parallel to the original…AQA
parallel field lines: Lines that run parallel to the axis, evenly spaced and all pointing the same way, showing the field is uniform.AQA
partial reflection: When an ultrasound pulse meets a boundary, some of it is reflected back towards the probe and the rest carries on into the second medium.AQA
Partial squares: Squares under the line that are not whole, which are combined to make whole ones when counting.AQA
particle arrangement: In a liquid the particles touch but slide past one another, while in a gas they are far apart and move randomly at speed.AQA
Particle arrangement in solids, liquids and gases: Solid particles are closely packed in a regular arrangement, liquid particles are close together but irregularly arranged, and gas particles are far apart.OCR
Particle collisions and force: Particles keep moving and colliding with the container walls, and each collision exerts a tiny push on the wall.OCR
Particle collisions producing force: Particles in a fluid move randomly and collide with surfaces, and each collision exerts a tiny force.OCR
particle count unchanged: The same particles are present before and after a change of state, so the number of particles is unchanged.AQA
particle model: A way of explaining the behaviour of a gas in terms of its molecules, including how far apart they are and how often they strike the container walls.AQA
particle model of a gas: The molecules of a gas are in constant random motion, and nothing about the molecules themselves changes size when the gas is heated; only how fast they move…AQA
Particle model of gases: The model in which gas particles move and strike the container walls, used to explain how temperature changes affect pressure at constant volume.OCR
Particle packing: How closely particles are packed, which with the mass of the particles density depends on.OCR
particle spacing: The air near the ground is the densest, with its particles closest together, and at higher altitudes the particles are spaced further apart.AQA
Particle spacing and its link to density: Density depends on how much mass is squeezed into a volume, which follows from particle spacing.OCR
Particle spacing and number density: In a larger volume the particles are spread more thinly, so the number of particles per unit volume falls.OCR
particles: The atoms and molecules that make up a system and store energy inside it.AQA
pascal: The unit in which pressure is measured, where 1 Pa is 1 N/m².AQA
Pascal (Pa): The unit of pressure, where one pascal is equal to one newton per square metre (1 Pa = 1 N/m²).AQA
Passenger safety and injury: A large force acting on a passenger can cause injury such as whiplash, internal damage or fractures.OCR
patterns and trends: These can be described in the use of energy resources, such as coal falling and gas and renewables rising as costs drop and targets tighten.AQA
peak wavelength: The wavelength at the peak of the curve, which shifts towards shorter wavelengths as the temperature increases.AQA
peer review: Other scientists read the method and the data, look for flaws in the design and check whether the conclusions genuinely follow from the results.AQA
penetrating: Gamma rays are highly penetrating, which suits them for sterilisation and medical treatments.AQA
penetrating power: Runs the other way: alpha is stopped by paper or skin, beta by a few millimetres of aluminium, and gamma is only reduced by thick lead or concrete.AQA, OCR
Penetrating power of alpha, beta and gamma: Gamma penetrates tissue and leaves the body, while alpha and beta are largely absorbed before reaching a detector.OCR
penetration: The extent to which alpha particles, beta particles and gamma rays pass through materials, such as paper, skin, aluminium, lead or concrete.AQA
Penetration and dose of X-rays and gamma rays: X-rays penetrate further and are absorbed by denser tissue such as bone, while gamma rays penetrate deeply and can damage cells throughout the body; a large…OCR
perceived versus measured risk: What people believe the danger to be, which is often higher than the measured risk.AQA
period: The time for one complete cycle, measured in seconds, s, and read from a displacement-time graph.AQA, OCR
period and peak value: Two features of a generator's output graph; spinning faster makes the peaks grow taller while the period gets shorter.AQA
Permanent Magnet: A magnet that produces its own magnetic field constantly.AQA
permanent magnets: A magnet that produces its own magnetic field all the time, with fixed north and south poles that are there whether or not another magnet is anywhere near.AQA, OCR
perpendicular components: Two components at right angles to each other that replace a single force acting at an angle.AQA
perpendicular distance: The distance between the pivot and the line of action of the force, which with the force explains the turning effect.AQA
Perpendicular distance from the pivot: The distance from the pivot to the line of action of the force, measured normal to the force's direction, in metres.OCR
perpendicular forces do no work: A force at right angles to the motion does no work, so a normal contact force transfers no energy when motion is perpendicular to it.AQA
physical change: A change in which the substance itself is unchanged, since only the arrangement and energy of its particles differ.AQA
Physical versus chemical change: A physical change alters the form or arrangement of a substance without making a new substance, while a chemical change produces a new substance with…OCR
pitch: What is heard as higher when a sound has a higher frequency.AQA
pitch and loudness: A higher frequency gives a higher pitch, and a larger amplitude gives a louder sound.AQA
pivot: The point about which an object turns, such as the centre of a nut, the hinges of a door or the wheel axle of a wheelbarrow.AQA
Pivot location: The fixed point about which an object actually turns, such as the hinge of a door or the nut on a spanner.OCR
planets: Bodies that orbit the Sun, are held in orbit by gravity, follow roughly circular orbits and give out no light of their own.AQA
Plastic deformation: Occurs when the object is permanently distorted and does not return to its original shape after the force is removed.OCR
plotting compass: Its north seeking pole is free to turn and settles along the field, so the needle points the way the field points.AQA
Plotting compass and iron filings as detection methods: A plotting compass placed near the wire deflects, and iron filings sprinkled on the card form concentric circles centred on the wire.OCR
plum pudding model: A ball of positive charge with the negative electrons dotted through it, which explained neutrality and the existence of electrons.AQA
Polarises: The field of a charged object polarises a neutral object, and the resulting force acts without the objects touching.OCR
poles of a magnet: The places where the magnetic forces are strongest.AQA
poles of a solenoid: The coil behaves as though it had a north pole at one end and a south pole at the other.AQA
political and economic factors: Political, social, ethical or economic considerations that mean science does not always have the power to deal with environmental issues.AQA
Position of colours within visible light: Within the visible band, red has the longest wavelength and lowest frequency, while violet has the shortest wavelength and highest frequency.OCR
Position of visible light in the spectrum: The visible region sits between infrared and ultraviolet, with violet near the short-wavelength end and red near the long-wavelength end.OCR
Positive and negative charge: Two kinds of charge exist, and charge exists in two types, positive and negative.OCR
Positive and negative charging by friction: Rubbing two different insulating materials transfers electrons from one object to the other; the object that gains electrons becomes negatively charged and…OCR
positive by loss of electrons: A positively charged object is one that has lost electrons, since only electrons move and the positive nuclei are fixed.AQA
positive charge: The material that loses electrons is left with an overall charge that is positive.AQA
positive direction: A direction chosen and stated first, so that forces the other way are treated as negative and the sign of the answer tells you the direction of the resultant.AQA
positive ions: Particles formed when atoms lose one or more outer electrons, so that positive charge outweighs negative.AQA
potential difference: Measured in volts (V), it is the energy transferred per unit charge, so 1 V means 1 J of energy is transferred for each coulomb of charge passing.AQA, OCR
Potential Difference (Voltage): The work done per unit charge moved between two points.OCR
Potential difference across coils: The voltage across the primary coil and the voltage across the secondary coil, related to the two turn counts by the transformer equation.OCR
Potential difference and current in coils: For an ideal transformer, the power input to the primary coil equals the power output from the secondary coil.OCR
Potential difference between live and neutral: The full mains value, while the potential difference between neutral and earth is close to zero.OCR
potential dividers: A thermistor connected in series with a fixed resistor across the supply forms a potential divider, so the share of the supply potential difference across the…AQA
potential energy of particles: Increases during a change of state, weakening the attractions that hold the particles close together while their kinetic energy stays the same.AQA
Power: The rate of energy transfer, so dividing useful power output by total power input gives the same fraction as dividing useful energy output by total energy…AQA, OCR
power and current: The power of a circuit device is related to the potential difference across it and the current through it.AQA
Power and energy calculations: The relations P = V × I and E = P × t link power, energy, potential difference, current and time.OCR
Power as a rate: The rate at which energy is transferred, not the total amount of energy transferred.OCR
power output in watts: Dividing the work done by the time gives a pair of values in watts, so the comparison becomes numbers.AQA
power rating: The power of the appliance, which together with how long it is switched on for determines the amount of energy transferred.AQA, OCR
Power transfer: An ideal transformer transfers the same power, so if potential difference rises the current falls by the same factor.OCR
powers of two: The factor the emission has fallen by is written as a power of two to get the number of half-lives.AQA
Practical applications: Uses such as broadcasting, cooking food, remote controls, fibre-optic communication, sterilising, medical imaging of bones and treating cancer.OCR
practical error analysis: Explaining how energy lost to the surroundings makes the calculated L too high, and how water evaporating before boiling makes L too low.AQA
Precision and repeat readings: Judging precision from the smallest division and repeating readings where possible.OCR
premature ageing: Repeated exposure damages the structural proteins keeping skin elastic, causing the skin to age prematurely.AQA
premature skin ageing: Ultraviolet waves are absorbed by the skin, leading to premature skin ageing and an increased risk of skin cancer.AQA
prenatal scanning: A medical use of ultrasound in which a developing foetus is scanned, chosen over X-rays because ultrasound is not ionising.AQA
Pressure: Force spread over the area in contact, measured in pascals (Pa), with force in newtons and area in square metres.AQA, OCR
Pressure (gas): The force exerted per unit area on the walls of a container, caused by the repeated collisions of gas particles with those walls.AQA
Pressure acting in all directions: The pressure from the weight of the air column acts in all directions on any surface within the air.OCR
Pressure and area: Because area appears on the bottom, a smaller area gives a larger pressure for the same force.AQA
pressure and volume: For a fixed mass of gas at a constant temperature, pressure multiplied by volume gives a constant value.AQA
Pressure as force per unit area: Measures how concentrated a force is over a surface, found by dividing the force normal to that surface by the area of the surface.OCR
Pressure at constant volume: With the number of particles and the space they occupy fixed, rising temperature raises the pressure and cooling lowers it.OCR
pressure difference: The difference between the pushes on the bottom and top faces depends on the vertical height of the block and the density of the liquid, not on how deep the…AQA
pressure falls with height: Atmospheric pressure decreases with an increase in height because there are fewer molecules above a surface and fewer collisions each second.AQA
Pressure from collisions with walls: Faster particles strike the container walls more often and with greater force, raising the pressure.OCR
Pressure in a liquid column: The pressure created at the base of a vertical column of liquid, calculated as height of column in metres × density of liquid in kg/m³ × gravitational field…OCR
Pressure in fluids: Pressure is calculated using p = F ÷ A, where F is the normal force in newtons and A is the area in square metres.AQA
Pressure in liquids: Increases with depth in a liquid, and the difference between two depths is found using Δp = ρ × g × Δh.OCR
Pressure increasing with density: Pressure increases with density because a denser liquid has more mass in the same volume.OCR
Pressure increasing with depth: Pressure in a liquid increases with depth because more liquid lies above and its weight presses down.OCR
pressure variations: A series of compressions and rarefactions in sound arriving at the microphone, so the air pressure at the diaphragm rises and falls.AQA
pressure with depth: Pressure in a liquid grows with depth, so the lower face of a submerged block sits deeper than the upper face and the liquid pushes harder on it.AQA
primary arrival: Being the faster of the two body waves, they are always the first arrival on a seismogram.AQA
primary coil: The coil connected to the input supply, which is simply whichever coil the input reaches.AQA
principal axis: A line drawn through the centre of the lens at right angles to the line representing the lens.AQA
principal focus: The point on the axis beyond the lens where parallel rays of light are brought to a focus.AQA
principle of moments: If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.AQA, OCR
Production of radio waves by oscillating currents: An oscillating current in a circuit produces radio waves, because accelerating charges radiate electromagnetic energy.OCR
Production of static electricity by rubbing insulators: Two different insulating surfaces are rubbed together, and friction transfers electrons from one surface to the other, producing static charge.OCR
projectiles: An object projected upwards has its kinetic store empty as its gravitational potential store fills, with some energy passing to the thermal store of the…AQA
Propagation of compressions through air: A vibrating source pushes air molecules back and forth, so a compression travels through the air while the air itself is not carried across the room.OCR
Proportional reasoning: Efficiency is a ratio and therefore has no unit, and can be written as a decimal or multiplied by 100 to give a percentage.AQA
Proportional reasoning with inverse relationships: Halving the volume of a fixed mass doubles the density, and quartering the volume raises density fourfold at constant mass.OCR
Proportional reasoning with ratios: Doubling the number of secondary turns while keeping the primary turns and primary potential difference fixed doubles the secondary potential difference.OCR
Proportionality symbol: The symbol in an expression like a ∝ F, which indicates how one variable changes with respect to another.AQA
protective precautions: Gloves are worn even though they cannot stop irradiation, because they prevent transfer of material.AQA
Protective role of insulation: Insulation around wires and the casing of devices prevents contact between the live conductor and a person or earthed metal, so intact insulation is a key…OCR
proton: The name given to the identical positively charged particles that make up the charge of a nucleus.AQA
Proton number and element identity: The number of protons fixes which element the atom is, so the nucleus of each element has a characteristic positive charge.OCR
proton number defines the element: An element is defined by the number of protons in its nucleus, so any process that changes that number makes a new element.AQA
protons and electrons: In an atom the number of electrons is equal to the number of protons in the nucleus.AQA
protons and neutrons: The particles that make up the nucleus, where protons have a relative charge of +1 and neutrons are uncharged.AQA
protostar: The hot dense lump at the centre of the collapsing cloud, which is not yet a star because fusion has not started.AQA
publishing unexpected results: Findings are published rather than kept in-house, so that a claim that challenges accepted theory gets tested rather than simply accepted or dismissed.AQA

Q

Q = I × t: The relationship between charge flow, current and time, which can be rearranged to I = Q ÷ t or t = Q ÷ I.OCR
Qualitative circuit reasoning: Describing the effect of added opposition or extra paths rather than deriving a formula.OCR
Qualitative description: Describing the transfers in words rather than giving a numerical calculation.OCR
Qualitative reasoning about change: You reason about the direction of the change, not a numerical calculation.OCR
Quantitative relationships: The equation is used by substituting the useful output energy transfer and total input energy transfer in joules (J) and dividing to obtain a decimal…AQA
quoting figures: Using specific numbers from the provided data to justify your reasoning in a conclusion.AQA

R

R = V ÷ I: Resistance is calculated as potential difference divided by current, and can be worked out for any component at any moment.AQA
radial spreading: The field lines spread out radially, so the same lines cover a larger and larger area as the distance grows.AQA
radiation balance: The balance between incoming radiation absorbed and radiation emitted, which determines the temperature of a body.AQA
radiation dose: The extra dose raises the chance of damage to cells, DNA and genes, and so of mutations or cancer.AQA
radioactive contamination: The unwanted presence of materials containing radioactive atoms on other materials.AQA
radioactive decay: A random process in which an unstable nucleus gives out radiation as it changes to become more stable.AQA
radiotherapy: High-energy gamma beams are aimed at a tumour from several directions so the beams cross only at the tumour, or a sealed source is implanted next to it.AQA
Radiotherapy and destruction of unwanted tissue: A targeted dose of radiation is aimed at the tissue so that its cells are damaged and stop dividing, which is how tumours are treated.OCR
radon and geology: Houses built on granite, as in parts of Cornwall and Aberdeen, receive far more radon than those on chalk or clay.AQA
random decay: You cannot predict which nucleus in a sample will decay next, and you cannot predict when any particular nucleus will decay.AQA
random error: Reduced by repeating the measurement and averaging the results.OCR
random motion: Molecules move continuously in every direction, with no preferred direction and a wide spread of speeds, changing direction whenever they collide with one…AQA
Random nature of decay: Emission happens randomly rather than at a set time and cannot be predicted for an individual nucleus.OCR
Random nature of radioactive decay: You cannot predict which particular nucleus will decay next, or exactly when it will happen.OCR
randomness: You cannot predict which nucleus in a sample will decay next, and you cannot predict when any particular nucleus will decay.AQA
range in air: The distance alpha particles, beta particles or gamma rays travel in air, from only a few centimetres to very large distances.AQA
Range of electromagnetic waves: Examples across the spectrum include visible light, microwaves, infrared, ultraviolet and X-rays, each transferring energy from a source to an absorber.OCR
range of half-lives: Half-life values span an extraordinary range, from tiny fractions of a second to billions of years.AQA
rarefactions: Regions where the particles are further apart, with lower than normal pressure.AQA
Rate equations and unit consistency: Computing a rate by dividing the correct numerator by the correct denominator and checking that the computed rate has sensible SI units.OCR
rate of change of momentum: The quantity equal to the force, which is made smaller when the same change in momentum is spread over more time.AQA
Rate of change of velocity: A large deceleration means a large rate of change of velocity, so a large resultant force acts.AQA, OCR
rate of cooling: How quickly a building loses energy and its inside temperature falls, which is lower when the walls conduct less readily.AQA
rate of cutting field lines: How fast field lines are being cut, which sets the size of what you induce.AQA
rate of emission: How much infrared radiation a body radiates in a given time, which is not the same as the total energy emitted over the whole experiment.AQA
Rate of energy transfer: How quickly energy passes across a material; a high thermal conductivity means a high rate for the same temperature difference and thickness.AQA, OCR
Rate of flow of charge: One ampere means one coulomb passing a point each second.OCR
Ratio and percentage calculation: The division gives a number with no unit; multiply by 100 to express it as a percentage.OCR
Ratio and proportional reasoning: Used in two ways: converting between units and computing rates.OCR
Ratio scaling with one variable held constant: Using ratio methods to scale consistently while keeping track of which variable changes and which is held constant.OCR
ray diagram: A drawing used to illustrate the refraction of a wave at the boundary between two different media.AQA
reaching a conclusion: Saying which figures support the decision and finishing with an explicit judgement that refers back to the figures given.AQA
reaction time: The delay between a stimulus and a response, measured in humans using methods such as the ruler drop.AQA, OCR
reactor shutdown: Dropping the control rods fully into the core, which shuts the reactor down.AQA
reading axes: Take the numbers from the axes rather than counting squares, unless the question states what one square represents.AQA
reading circuit diagrams: Following the steps in the order the diagram shows, starting at the switch and following the current, because each linked step earns credit.AQA
reading decay graphs: Correct for background, halve the initial count rate, read across to the curve and down to the time axis.AQA
reading graphs: On a curved graph, R = V ÷ I is recalculated at each point rather than using one value throughout.AQA
real focus: The focus is real because real light rays actually meet there, so a screen placed at that point shows a bright spot.AQA
real image: Formed when the object is further from the lens than the principal focus, so the refracted rays actually cross beyond the lens; it is inverted and can be…AQA
real versus virtual: A convex lens can form a real image, whereas a concave lens can only form a virtual image.AQA
Real-life applications of deformation: Examples include a gymnast's uneven bars bending under her weight and the reaction at the supports, a bridge deck flexing under traffic, and a rubber band…OCR
rearrangement: Making a quantity the subject of an equation, such as rearranging the elastic energy equation to make the spring constant the subject.AQA
rearranging: The equation can be rearranged so that speed equals distance divided by time and time equals distance divided by speed.OCR
Rearranging and applying a physics equation: Always square the speed first, then multiply by mass, then halve.OCR
Rearranging and applying equations: Dividing gravitational potential energy by the product of mass and gravitational field strength finds height, or by the product of gravitational field…OCR
Rearranging and substituting into a kinematic equation: List the known quantities with units, rearrange for the unknown, substitute values and solve.AQA
Rearranging equations: Rearranging gives change in velocity = acceleration × time and time = change in velocity ÷ acceleration, useful when the question supplies different quantities.AQA, OCR
Rearranging equations and SI units: Dividing the force by the product of the other two values gives the rearranged quantity, after converting all values to SI units first.OCR
Rearranging equations to solve for any variable: Rearranged, the spring constant equals force divided by extension, and extension equals force divided by spring constant.OCR
Rearranging formulae: The relationship can be rearranged to find mass as force ÷ acceleration, or acceleration as force ÷ mass.OCR
rearranging moments: Making the unknown force or distance the subject of the moment equation after setting the total clockwise moment equal to the total anticlockwise moment.AQA
Rearranging ratio equations: Cross-multiplying so that the primary voltage times the secondary turns equals the secondary voltage times the primary turns, isolating the unknown quantity.OCR
Rearranging the density equation: To find mass use m = ρ × V; to find volume use V = m / ρ.OCR
Rearranging the equation: Rearranging lets you find either height, since image height = magnification × object height.AQA, OCR
Rearranging the momentum equation: The equation p = m × v can be rearranged to find mass or velocity when momentum is known.OCR
Rearranging v = f × λ: Selecting the formula and rearranging it to suit the quantity you need, whether velocity, frequency or wavelength.OCR
Recall: Writing either efficiency equation from memory.AQA
Recall and application of equations: Recall means writing the equation from memory; apply means substituting values, rearranging and calculating.AQA
receding galaxies: Galaxies moving away from us, shown by red-shift observed in almost all galaxies, while a few nearby galaxies are blue-shifted because they are approaching.AQA
reciprocal relationship: Period and frequency are reciprocals: T = 1 ÷ f.AQA
Recognising component-specific symbols: A variable resistor is a rectangle with an arrow through it, a fixed resistor is a plain rectangle, and a switch is a break in the line with a hinged arm.OCR
Recognising correct values among distractors: A useful check is to reject any option that gives a direct supply, a frequency such as 60 Hz, or a voltage far from 230 V.OCR
Recording mass, time, volume and temperature with units: Recording each reading with its correct unit and an appropriate number of significant figures, matching the precision to the smallest scale division.OCR
Recording values with units: Writing every value with its unit and an appropriate number of significant figures.OCR
Recording with units and significant figures: Recording each measurement with its unit and a sensible number of significant figures.OCR
Recovery of original properties: When a physical change is reversed, the material regains its original properties, such as the same melting point, density and appearance as before.OCR
rectangle construction: Given two perpendicular forces, draw them as the sides of a rectangle from a common starting point and complete the rectangle.AQA
rectangles and triangles: The shapes into which the area under straight-line sections is split, a rectangle being velocity multiplied by time and a triangle half the base multiplied by…AQA
red end of the spectrum: The long wavelength end of visible light, which runs from violet at the short wavelength end to red at the long wavelength end.AQA
red giant and red supergiant: A star like the Sun becomes a red giant, while a much more massive star becomes a red supergiant.AQA
red to violet: Inside the visible band, red has the longest wavelength and lowest frequency of the visible colours and violet the shortest and highest.AQA
red-shift: An observed increase in the wavelength of light from most distant galaxies, called red-shift because red is the longest wavelength of visible light.AQA
Red-shift as supporting evidence: Nearly all galaxies show light shifted to longer wavelengths, indicating they recede, and more distant galaxies recede faster, which fits expansion from a…OCR
Red-shift of galactic light: Light from a receding galaxy is stretched to longer wavelengths, so its spectral lines shift towards the red end.OCR
Reducing air resistance: Streamlining shapes so air resistance is reduced and therefore less energy is transferred wastefully.OCR
Reducing friction: Lubricating moving parts so friction transfers less energy to thermal stores, which reduces the energy dissipated as heat.OCR
Reducing heat loss by insulation: Insulating or lagging a device so less heat escapes to the surroundings.OCR
Reducing measurement error: Reducing error by repeating readings or by timing multiple oscillations and dividing to find one period.OCR
Reducing random and reaction-time error: Reducing timing error by using electronic timing where possible or by repeating readings.OCR
Reducing random error by repeating: Taking repeated readings, such as timing several repeats, and averaging to reduce random error.OCR
reducing unwanted transfers: Unwanted energy transfers can be significantly reduced, though never entirely eliminated, using methods such as lubrication and thermal insulation.AQA
refining a model: The nuclear model was not thrown away when the neutron turned up, it was completed.AQA
Reflection: Sends the wave back into the first material at the boundary, as when ultrasound pulses bounce off the boundary between soft tissue and bone or off the seabed…AQA, OCR
reflection by clouds and ice: The fraction reflected straight back into space without ever being absorbed, mainly by clouds, ice and snow.AQA
reflection into space: Part of the incoming radiation is reflected straight back to space by clouds, snow and ice.AQA
refraction: The change in direction of electromagnetic waves when their velocity changes on entering a different substance.AQA, OCR
refraction at the core boundary: The change of direction of P-waves as they enter the core, where their speed changes.AQA
refraction at two surfaces: Every ray is refracted twice, once at each curved surface, because light slows down when it enters glass and speeds up when it leaves.AQA
refraction inside the Earth: A change of speed at a boundary refracts the wave, bending its path, so P-waves do not travel in straight lines through the Earth.AQA
regular and irregular solids: Objects whose volume can be found from measured dimensions, and objects whose volume cannot be calculated and so is found by displacement.AQA
Relationship between velocity, acceleration and distance: The change in the square of velocity is linked to acceleration and distance by v ² − u ² = 2 a s.AQA
relative charge: Every proton carries a relative charge of +1 and every electron a relative charge of -1.AQA
relative charge and mass: A proton has a relative charge of +1 and a relative mass of 1, the same mass as a neutron.AQA
Relative size of nucleus and atom: The nuclear radius is much smaller than the radius of the whole atom.OCR
relays and electromagnetic switches: Devices in which closing the switch drives a current through the electromagnet, and the moving arm does something mechanical, letting a small current switch a…AQA
reliability: Some energy resources are more reliable than others because they do not depend on the weather, and tidal power is reliable because it is predictable.AQA
Reliability and repeat readings: Recording repeat readings and identifying the point at which the spring stops extending proportionally to the force.OCR
Reliability and repeats: Repeating the test and averaging reduces random error.OCR
Reliability through repetition: Repeating a measurement, such as a temperature rise, to check that the observation is reliable and noting whether results agree.OCR
removal from the field: Taking the external field away, which the mark scheme allows as 'when there are no magnets nearby'.AQA
renewable: Describes resources such as bio-fuel, wind, hydroelectricity, geothermal, the tides, the Sun and water waves, which are replenished as they are used.AQA
Renewable resources: Resources such as biofuel, wind, hydroelectricity, tides and the Sun that are replenished naturally.OCR
Repeated halving: A useful method is to halve the count rate repeatedly and add the half-life each time until you reach the measured value.OCR
repeats and means: Each timing is repeated at least three times, a mean is taken, and any obvious anomaly is discarded.AQA
replenished: Being replaced as it is used, which is the property the mark scheme wants for renewable.AQA
representing pairs as vectors: Drawn as vectors, the pair is two arrows of equal length pointing in opposite directions, each drawn on the object it acts on.AQA
Representing strength by field-line spacing: Field lines drawn closer together represent a stronger field.OCR
representing vectors: A vector quantity may be represented by an arrow, because the arrow carries both pieces of information at once.AQA
reproducibility: Other groups repeat the study independently, which tests whether the findings are reproducible rather than a product of one team's equipment, sample or bias.AQA
repulsion between nuclei: Both nuclei are positively charged and repel one another, so they need enough kinetic energy to collide and join.AQA
required practical 4: An activity in which circuit diagrams are used to construct appropriate circuits to investigate the I–V characteristics of a variety of circuit elements.AQA
required practical 8: Making observations to identify the suitability of apparatus to measure the frequency, wavelength and speed of waves in a ripple tank and waves in a solid and…AQA
Resistance: Obtained from the potential difference across a component divided by the current through it, with the unit stated as the ohm.AQA, OCR
Resistance and Ohm's law: The relation V = I × R links potential difference, current and resistance.OCR
resistance falls as temperature rises: The relationship in a thermistor, where warming it makes its resistance fall and cooling it makes its resistance rise.AQA
resistance of damp skin: Damp skin has a much lower resistance, so the same 230 V drives a larger current.AQA
resistances add: The total resistance of two components is the sum of the resistance of each component, R = R₁ + R₂.AQA
resistors and diodes: A fixed resistor is a plain rectangle, a variable resistor is a rectangle with an arrow through it, and a diode is a triangle against a bar.AQA
resolution: The finer detail given by the shorter wavelength of high frequencies, which reflects well from small objects.AQA
Resolution and precision: Choosing the instrument that can measure the smallest change required, such as the scale that gives suitable resolution.OCR
Resolution into perpendicular components: Drawing a force as the diagonal of a rectangle so the two perpendicular components can be read from the sides.OCR
resolving a force: Splitting a single force into two components acting at right angles to each other.AQA
resultant: What forces combine to give; along a straight line, forces pointing the same way add and forces pointing opposite ways subtract.AQA, OCR
Resultant force: When several forces lead to a resultant force on an object, a zero resultant force means the object stays at rest or keeps a constant velocity.AQA, OCR
Resultant force and acceleration: The force used in the relationship is the resultant (net) force, so any opposing force is subtracted first.OCR
Resultant force and direction: When several forces act, F means the resultant force, found by combining them along the line of motion, and its direction should be stated where a question…AQA
Resultant force of zero: The special case where the forces cancel, meaning the object stays at rest or moves with constant velocity.OCR
Resultant force on a single body: The forces on one body only are combined to judge the resultant.OCR
resultant moment: What exists when the two totals are not equal, and the beam turns the way the larger one points.AQA
resultant of two forces: The single force drawn from the tail of the first arrow to the tip of the second, measured and converted with the scale, with its direction given as an angle…AQA
Resultant turning force: When two forces act, their turning effects are compared to decide the resultant direction.OCR
return path: The route by which charge driven out along the live wire has to get back, provided by the neutral wire.AQA
Reversibility: The distinguishing feature of a physical change, where reversing the change restores the material's original properties.OCR
Reversibility of shape change: The key distinction is reversibility: elastic deformation is reversible, plastic deformation is not.OCR
reversing current or field: Reverse either the current or the field and the force reverses; reverse both and it is unchanged.AQA
reversing the current: Which end is which depends on the direction of the current around the turns, so reversing the current swaps the poles.AQA
reversing the magnet: Turn the magnet round and the induced poles swap as well, so it is attraction once again.AQA
reversing the motion: Pulling a magnet out of a coil instead of pushing it in makes the galvanometer needle swing the other way.AQA
reversing the poles: Turning the magnet round so that the south pole goes in first makes the needle swing the other way again, because the field direction has reversed.AQA
right angles to the field: The force is greatest when the wire is at right angles to the field, and falls to zero when the wire lies along the field.AQA
right hand grip rule: Point the right thumb along the conventional current and the curled fingers give the direction of the field, so reversing the current reverses the field.AQA
Right-hand grip rule and effect of reversing current: Looking along the wire with the conventional current flowing away from you, the field lines run clockwise; reversing the current reverses the field direction.OCR
ripple tank: Apparatus in which a motorised dipper makes straight ripples whose shadows fall on paper below, used to measure the frequency, wavelength and speed of water…AQA
risk comparison: Calculating a comparison, such as a ratio or a difference, between two radiation doses to conclude which carries a higher risk.AQA
risk of harm: What a radiation dose in sieverts measures, resulting from an exposure of the body to the radiation.AQA
risk to tissue: Radiation dose measures the risk of harm to body tissue from being exposed to radiation, taking account of the amount absorbed and how damaging that type is.AQA
Role of evidence in changing scientific models: Each change happened because experimental evidence did not fit the previous model.OCR
roughly equal fragments: The two smaller nuclei the nucleus splits into, roughly equal in size, though not identical.AQA
ruler drop test: One student releases a metre rule between another's fingers and the catch distance is converted to a time.AQA
running time: The time an appliance is used for, which must be combined with the rating using E = P t to compare appliances properly.AQA
Rutherford, Geiger and Marsden alpha-particle scattering: Alpha particles fired at thin gold foil mostly passed straight through but some were deflected strongly.OCR

S

S-wave shadow: A huge shadow covering most of the far side of the globe, left because S-waves stop at the boundary of the liquid outer core.AQA
safe after removal: As soon as the radioactive source is removed or shielded, the object emits nothing and can be handled safely.AQA
Safe handling of energy-measuring equipment: Using the apparatus safely, for example clamping hot equipment, keeping the circuit within its rating and avoiding contact with heated surfaces.OCR
safety features: Things such as air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for playgrounds, which crumple, stretch or compress so a…AQA
safety implications: Conclusions that follow from the figures, such as leaving a longer gap in the wet because speed limits and larger gaps in poor conditions matter far more than…AQA
same current throughout: There is the same current through each component, because there is only one path and charge is not used up.AQA
same effect on the object: The single force replacing the original forces has exactly the same effect on the object as all of them acting together.AQA
same energy different time: Both motors do the same work and transfer the same energy, but the motor that finishes in half the time has twice the power.AQA
same speed in a vacuum: All electromagnetic waves travel at the same velocity through a vacuum or air, so ultraviolet and visible light from the Sun arrive together.AQA
same unit for both heights: Image height and object height should both be measured in either mm or cm, because mixing them makes the answer ten times too big or too small.AQA
scalar and vector: Speed is a scalar and velocity is a vector, so velocity carries a direction with it.AQA
scalar quantities: Distance is one, meaning the total distance travelled can be plotted regardless of whether the path is straight or curved.AQA
scalar quantity: A quantity that is completely described by a number and a unit, its magnitude, with no direction attached.AQA
scalars: Quantities such as distance and speed that have magnitude only and no direction.AQA
scale conversion: Measure the diagonal and convert it with the stated scale to get the magnitude.AQA
scale diagrams: From one of these, the straight line from start to finish is measured with a ruler, converted with the scale, then the angle is measured with a protractor.AQA
scale drawing: A diagram in which the length of the arrow represents the magnitude and the direction of the arrow the direction of the vector quantity.AQA
Scale of atoms and small molecules: Typically 1 × 10⁻¹⁰ m, which is 0.1 nm, or one ten-billionth of a metre.OCR
scale of the universe: The order in which moons orbit planets, planets orbit a star, stars sit within a galaxy, and galaxies together make up the universe.AQA
scale vector diagrams: Drawings in which a stated scale, such as 1 cm represents 20 N, is used to show forces to length and direction.AQA
scaled arrows: How a vector is drawn on a diagram, with length drawn to scale and direction being the direction of the quantity.AQA
scaling values: Using the proportionality to change a value, such as doubling the mass to double the weight.AQA
Scattering at rough surfaces: Light is reflected in many directions at a rough surface, so no clear image forms and the surface looks matt.OCR
science is provisional: Theories are built from observations and are changed when new observations do not fit, which is what happened in 1998.AQA
scientific models: The best current explanation of the evidence, not a permanent truth.AQA
scope of the specification: Neutrinos, binding energy, decay chains and the details of what holds a nucleus together are all outside this specification.AQA
sealed sources: Sources that add protection against contamination as well as limiting irradiation.AQA
secondary coil: The coil connected to the output, which is not joined electrically to the primary coil.AQA
Selecting apparatus for speed, frequency and wavelength: Matching the instrument to the quantity, such as a metre rule for wavelength and a timer for frequency.OCR
Selecting the correct formula for the required quantity: Choosing the form of the wave formula that gives the quantity needed, then substituting values converted into SI units.OCR
Selection of appropriate measuring apparatus: Choosing apparatus that matches the energy quantity being measured, such as a joulemeter for electrical energy or a force meter and rule for work done.OCR
selective reflection: The surface reflects some wavelengths much more strongly than others, and the mixture reflected into the eye is the colour perceived.AQA
self limiting heating: The process in which a body getting hotter increases its own rate of emission, so the gap between the two rates narrows.AQA
self-sustaining: Describes a sequence in which the neutrons released by fission go on to cause further fissions, so the reaction keeps going.AQA
sensing light: The role of an LDR, which makes it a light sensor rather than a source of energy.AQA
Separate-science scope: Content assessed only in the physics separate science qualification, treated as separate-science scope even though the row is listed for both tiers.OCR
series and parallel: Components in series sit on one loop so the same current passes through each, while components in parallel sit on separate branches across the same two points.AQA
Series and parallel circuits: In series the same current passes through each resistor in turn, whereas in parallel the current splits between alternative branches.OCR
series and parallel effects: A parallel branch lowers the total resistance and raises the current, whereas resistors added in series raise the total resistance and lower the current.AQA
Series and parallel placement of meters: An ammeter is a circle with A placed in series, and a voltmeter is a circle with V placed in parallel across a component.OCR
series circuit: A circuit in which the current is the same at every point, the supply potential difference is shared between components, and resistances add.AQA, OCR
series connection: Two components are in series when they sit in the same single loop, joined end to end, so every unit of charge that leaves the cell must pass through both.AQA
series loop current: A current has the same value at any point in a single closed loop.AQA
Series versus parallel arrangement: In series, components sit on one path so the same current passes through each; in parallel, branches split the current.OCR
shadow zones: Patterns in seismic records where expected waves failed to arrive, which the earlier models could not explain.AQA
shared construction rays: Both lens types use the same two construction rays: one through the centre that carries straight on and one arriving parallel to the principal axis.AQA
shared potential difference: The total potential difference of the power supply is shared between the components, and the individual values add to the supply value.AQA
shearing the rock: The rock is sheared from side to side rather than squeezed, which only works where the material resists a change of shape.AQA
shiny silver worst: The shiny silver face gives the lowest reading, showing that a shiny silver surface is the worst emitter of infrared.AQA
short and long wavelength radiation: Short wavelength radiation arrives from the Sun, while the warmed surface emits long wavelength infrared.AQA
Short half-life: The material decays quickly, so its activity and hazard fall rapidly, but it emits intensely while fresh.OCR
shortest wavelength: Gamma rays sit at the highest frequency and shortest wavelength end of the electromagnetic spectrum.AQA
SI units: The stated units are the metre, the metre per second and the second, and every quantity is converted to these before substituting.OCR
SI units and prefix conversion: Converting prefixes first, so kilohertz becomes hertz and centimetres become metres, before substituting values.OCR
SI units and substitution: Values are substituted with consistent SI units before calculating, such as m/s, m/s² and m.AQA
SI units and unit consistency: Pressure is in pascals (Pa), force in newtons (N) and area in square metres (m²); keep units consistent and convert cm² to m² before substituting.AQA
SI units and unit conversion: Keep units consistent before substituting, converting grams to kilograms and kilometres per hour to metres per second where needed.AQA, OCR
sievert and millisievert: Radiation dose is measured in sieverts (Sv), and 1000 millisieverts (mSv) = 1 sievert (Sv).AQA
Sign convention: The chosen positive direction, which must be stated when the motion is not in a single straight line, so that a final velocity can be negative if the motion…AQA
sign conventions: Handling direction along a single line with positive and negative signs, for example taking east as positive.AQA
Sign conventions for direction: Motion above the axis gives positive displacement, while a region below the axis gives negative displacement, so areas on opposite sides must be subtracted to…OCR
significant figures: A sensible number of these is used when recording each measurement, together with the correct unit.OCR
Significant figures and units: An estimate should be rounded to a sensible number of significant figures, with units converted if needed and the force given in newtons.AQA
silvered surfaces: Surfaces that are poor at both absorbing and emitting, which is exactly why a vacuum flask is silvered inside.AQA
Simple hydraulic system: Uses a liquid, which is virtually incompressible, to transmit pressure, so a larger piston area gives a larger output force.OCR
single alpha decay: Decay in which one alpha particle, written in full as ⁴₂He, is emitted, so a second particle is not added.AQA
single bend at the lens line: The refraction is shown as a single bend at that line rather than at two curved glass surfaces, which is the standard simplification for GCSE ray diagrams.AQA
single beta decay: Decay in which one beta particle, written in full as ⁰₋₁e, is emitted, so a second particle is not added.AQA
single path: In a series circuit there is only one path, so an ammeter reads the same wherever you place it.AQA
skin cancer risk: Mutations caused by genetic damage significantly increase the risk of developing skin cancer.AQA
slip rings: Two rings, one joined to each end of the coil, each with a brush pressing on it, so each end keeps its own ring all the way round.AQA
slope: The feature of a line that gives speed on a distance-time graph and acceleration on a velocity-time graph.OCR
slower than P-waves: Roughly half to two thirds of the P-wave speed in the same rock, which is why they arrive second.AQA
small bar magnet: The part inside a compass that is free to rotate and lines up with the direction of the magnetic field it is in.AQA
smooth curve: The shape of the trace drawn for a generator's output, rather than straight lines or a square wave.AQA
soft iron and steel: Soft iron loses essentially all of its magnetism at once, while steel is harder and keeps a good deal.AQA
soft tissue imaging: A medical use of ultrasound for imaging soft tissue such as the heart and liver.AQA
solar cells: Sunlight is absorbed by a solar cell and the energy is transferred to an electrical store.AQA
solar system within a galaxy: Our solar system is a small part of the Milky Way galaxy.AQA
solenoid: A long coil of wire, and shaping a wire into one increases the strength of the magnetic field created by a current through the wire.AQA
solenoid field pattern: The field outside a solenoid has the same shape as the field of a bar magnet, with lines running from the north end round to the south end.AQA
solid inner core: The part of the core revealed by faint refracted P-wave arrivals inside the shadow.AQA
solid sphere model: The earliest scientific model of the atom, set out by John Dalton, treated each atom as a tiny solid sphere with no internal structure and no parts.AQA
Sonar: Relies on strong reflection at the water–seabed interface, with ultrasound pulses reflecting from the seabed and returning to the detector.OCR
sound and water waves: For ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels.AQA
sound to vibration: Pressure variations in air push on the ear drum, the drum vibrates, the ossicles pass the vibration to the cochlea, and nerve impulses travel to the brain.AQA
sound waves: A mechanical wave carried by the vibration of the particles of a medium, travelling through air as a longitudinal wave.AQA
source activity: The strength of the source, on which the dose depends.AQA
source and absorber: Energy leaves a source, travels as a wave with nothing material moving between them, and is transferred to a store in the absorber.AQA, OCR
Source of potential difference: One condition for charge to flow, such as a cell or battery, which pushes the charge.OCR
source stays separate: The radioactive source remains separate from the object, with no radioactive material transferred.AQA
sources of ac and dc: Cells, batteries and solar cells are dc sources, while generators produce ac and transformers work only with ac.AQA
sources of error: Energy transferred to the container and the surroundings, which makes the experimental value too high.AQA
spacing and wavelength: Inside the slower medium the fronts are closer together, because the frequency is unchanged and the speed has fallen, so the wavelength must be shorter.AQA
spacing in solids liquids gases: In a solid the particles are touching, in a liquid touching or nearly touching with a few gaps, and in a gas well separated.AQA
spanners and levers: Examples in which a force applied at a distance from a pivot causes rotation, a longer handle giving a larger turning effect for the same force.AQA
sparking: A strong field near a highly charged object pulls electrons free from air molecules, so the air conducts and charge crosses the gap.AQA
sparking distance: As an earthed conductor is moved towards a charged dome, the field in the gap grows stronger until the air breaks down.AQA
Sparking from built-up charge: A spark can occur when the built-up charge is large enough to jump across a gap, for example from a charged object to a conductor.OCR
specific heat capacity: The energy needed for a temperature rise depends on the mass, the temperature change and this quantity, and a larger value means more energy is needed for the…AQA, OCR
Specific heat capacity relationship: The relationship ΔE = m × c × Δθ links energy change to mass, specific heat capacity and temperature change.OCR
Specific latent heat: The energy per kilogram to change state with no change of temperature, unit J/kg, governing the flat parts of a heating graph.AQA, OCR
Specific latent heat of fusion: The energy needed to change the state of 1 kg of a substance by melting or freezing, with no change in temperature.AQA, OCR
Specific latent heat of vaporisation: The energy needed to change the state of 1 kg of a substance by boiling or condensing, with no change in temperature.AQA, OCR
specular reflection: Reflection from a smooth surface such as a plane mirror, which sends a parallel beam back as a parallel beam so a clear image is seen.AQA
Specular reflection at smooth surfaces: Parallel rays reflect in one direction at a smooth surface, and a clear image can form.OCR
speed: Distance divided by time, found using a metre rule or tape to measure the distance and a stopwatch or light gates to measure the time.OCR
speed as a scalar: A quantity that says how quickly distance is covered and nothing about which way, having magnitude only.AQA
speed depends on medium: The speed of a seismic wave depends on the properties of the material it is passing through, so it changes sharply when a P-wave crosses from the solid mantle…AQA
speed equals distance over time: Using speed = distance / time with the speed in the correct medium, then halving the calculated distance because the pulse travels to the boundary and back.AQA
speed in different media: The speed changes because the medium has changed, since the speed depends on the medium.AQA
Speed of light: For EM waves in a vacuum, v is about 3.0 × 10⁸ m/s.OCR
Speed of light in a vacuum: The velocity at which all electromagnetic waves travel in space, approximately 3.0 × 10⁸ m/s.OCR
speed of movement: Moving the magnet or the coil faster raises the induced potential difference.AQA
Speed of recession and distance: The more distant a galaxy is, the faster it recedes, and the faster the recession, the greater the red-shift.OCR
speed of sound in air: A typical value for this is 330 m/s, the value to use whenever a question about sound in air supplies none.AQA, OCR
speed of sound in water: The speed used with speed = distance / time for a pulse travelling in water, about 1500 m/s in sea water.AQA
Speed squared: Because speed is squared, doubling the speed multiplies kinetic energy by four, while doubling the mass only doubles it.OCR
split-ring commutator: A ring cut into two halves, so that every half turn the halves change brushes and swap the connections at exactly the moment the induced potential difference…AQA, Pearson Edexcel
spontaneous fission: A uranium-235 nucleus can split entirely on its own, but this is rare.AQA
spread out positive charge: The whole atom is a sphere of positive charge, spread out evenly through its volume.AQA
spring constant: A measure of stiffness, found by rearranging F = kx to give k = F ÷ x, where F is the applied force in newtons and x is the extension in metres.AQA, OCR
Spring constant and gradient: Force divided by extension equals the spring constant k, and the gradient of the straight section of a force–extension graph gives k.OCR
Squaring velocities before subtraction: Each velocity is squared first, then the square of the initial velocity is subtracted from the square of the final velocity.OCR
Stable orbit: A satellite stays in a stable circular orbit when gravity supplies exactly the centripetal force it needs.OCR
stable orbits: Gravity is stronger closer in, so a satellite in a low orbit has to travel faster to stay there, and if the speed increases the radius must decrease.AQA
stage speed: The speed during one stage comes from the gradient of that stage alone.AQA
staged journeys: Where the motion is not steady, apply the equation stage by stage and add the distances.AQA
Standard circuit symbols: A shared drawing code in which a diode is a triangle with a bar, an LDR is a resistor box with arrows pointing in, and a filament lamp is a circle with a cross.AQA, OCR
Standard equals sign: The sign used for standard calculations rounded to an appropriate number of significant figures, rather than for approximations.AQA
standard lens symbols: A convex, converging lens is drawn as a vertical line with outward pointing arrowheads at both ends, and a concave, diverging lens as a vertical line with…AQA
standard symbols: Circuit diagrams use standard symbols, so every component has one agreed symbol and any physicist can read any diagram.AQA
start of fusion: The point when the core is hot and dense enough for hydrogen nuclei to fuse, and the object becomes a main sequence star.AQA
states of matter: Solid, liquid and gas forms, differing in density because of the arrangement of atoms or molecules and the gaps between them.AQA
Static Electricity: A build-up of stationary electric charge on the surface of an insulating material.Pearson Edexcel
stating a displacement: This means writing three things: a number, a unit and a direction, such as a compass point, a bearing or an angle to a stated line.AQA
stating assumptions: Giving an assumption such as the conductor being at right angles to the field or the field being uniform, which examiners ask you to state.AQA
stationary period: A period shown on a distance–time graph as a horizontal line lasting exactly as long as the description states.AQA
Statistical behaviour of large samples: Despite the randomness of individual decays, a large sample shows a predictable statistical pattern.OCR
steady output: A reactor held at a steady rate, which means exactly one neutron from each fission going on to cause the next.AQA
steepest curve: On a graph of several isotopes, the steepest initial curve belongs to the isotope with the shortest half-life, because it decays quickest.AQA
steepness of decay curve: For the same number of nuclei, the isotope with the shortest half-life has the steepest curve at the start.AQA
stellar life cycle: The series of stages a star goes through, which is determined by the size of the star.AQA
step-down transformer: A transformer that has fewer turns on the secondary coil than the primary and is used to decrease the potential difference to a much lower, safe value for…AQA, OCR
Step-up and step-down transformers: A step-up transformer has more turns on the secondary coil than on the primary coil and gives a larger secondary potential difference; a step-down transformer…OCR
step-up transformer: A transformer that has more turns on the secondary coil than the primary and is used to increase the potential difference from the power station to the…AQA, OCR
sterilisation: Gamma irradiation is used to sterilise surgical instruments and food because the radiation kills bacteria as it passes through the sealed packet.AQA
stiffness: A property measured by the spring constant, where a stiffer spring needs more force for the same extension and so has a larger k.OCR
stopping distance: The sum of the distance the vehicle travels during the driver's reaction time and the distance it travels under the braking force.AQA, OCR
straight line through the origin: The evidence for proportionality on a graph of current against potential difference; a straight line that misses the origin shows a linear relationship but…AQA
Streamlining: A change that lowers drag, so less energy is transferred to the air.AQA
strength of the field: A stronger magnet gives more field lines to cut in the same space, so the induced potential difference rises.AQA
stretching, bending and compressing: Ways of changing the shape of an object, for which students should be able to give examples of the forces involved.AQA
stronger field: Bringing two charged objects closer means the second object moves into a region where the first object's field is stronger.AQA
strongest at the poles: The field is strongest at the poles of the magnet, where the field lines are packed closest together.AQA
structure of the atmosphere: A thin layer of air round the Earth, thin relative to the size of the Earth.AQA
Structure of the atom: A positively charged nucleus surrounded by negatively charged electrons.OCR
Structure of the solar system: The Sun and eight planets in order from the Sun, with minor planets also orbiting the Sun and most planets having moons that orbit them.OCR
subdividing nuclear charge: The idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles.AQA
submerged object: An object that is partially or totally under a liquid, experiencing a greater pressure on its bottom surface than on its top surface.AQA
supernova: The explosion of a massive star that ends its life and distributes the elements throughout the universe.AQA
supernova observations: Observations of supernovae of one particular type, which always explode with about the same peak brightness, used to measure the distances of very distant…AQA
surface colour: Black surfaces absorb more infrared than white surfaces, as shown by the temperature rises of the cubes.AQA
switchable magnetism: The magnetic field exists only while there is a current in the coil, so it can be switched on and off, unlike a permanent magnet.AQA
Symbols for alpha, beta and gamma emissions: The emitted particles written with their own numbers: an alpha particle as ⁴₂He, a beta particle as ⁰₋₁e, and a gamma photon as ⁰₀γ.OCR
symbols for emitted particles: An alpha particle may be represented by one symbol and a beta particle by another in a nuclear equation.AQA
system: An object or group of objects, whatever you choose to draw a boundary around.AQA

T

tangent: A line drawn to a curve at a specific time whose gradient gives instantaneous acceleration.AQA
Temperature: A measure of the average kinetic energy of the molecules, not of any one molecule and not of the total.AQA
temperature and mean kinetic energy: Temperature is a measure of the mean kinetic energy of the molecules, so it controls how hard each impact is and how many impacts happen each second.AQA
Temperature and particle speed: Raising the temperature increases the average kinetic energy of the particles, so they move faster.OCR
temperature and resistance: The resistance of a filament increases as the temperature of the filament increases.AQA
Temperature as a measure of average particle kinetic energy: The increased average kinetic energy of the particles corresponds to a higher temperature of the gas.OCR
temperature change: The difference between the start and finish temperatures, written as final minus initial and used rather than the final temperature.AQA, OCR
Temperature change calculation: Work out the temperature change by subtracting the initial temperature from the final temperature.OCR
temperature control: As the room warms the thermistor resistance falls and the potential difference across it falls, and when that reading drops past a set value the control…AQA
temperature dependence: The intensity and wavelength distribution of any emission depends on the temperature of the body, with intensity increasing at every wavelength as temperature…AQA
Temperature dependence of resistance: Heating raises the resistance of a filament lamp, so the current rises less steeply at higher voltages.OCR
temperature rise: What happens when the energy supplied goes to the kinetic store of the particles, with the rise depending on the mass, the specific heat capacity and the…AQA
temperature sensor: A device that shows a change in surroundings directly as a change in an electrical reading, which a thermistor does.AQA
tension: The pull along a stretched rope, cable or spring, pulling inwards on whatever is attached at each end.AQA
terminal velocity: Air resistance has grown until it equals the weight, so the single force replacing them is zero and the velocity stops changing.AQA
terrain: Walking uphill, on sand or over rough ground is slower than on a level pavement, because more work is done against gravity and against friction.AQA
test charge: A second charged object placed in the field, which experiences a force and is used to detect the field.AQA
test for a magnet: Repulsion is the only sure test for a magnet, because attraction proves nothing.AQA
test for charge: Repulsion is the more useful test, because attraction also happens between a charged object and an uncharged one, whereas only two like-charged objects repel.AQA
the Big Bang model: The theory reached by running the expansion backwards to a hot dense beginning, supported by red-shift as evidence.AQA
The eight planets and minor planets: Our solar system contains the Sun and eight planets in order from the Sun, while minor planets also orbit the Sun but are much smaller than planets.OCR
the joule: The energy transferred when a force of one newton moves an object one metre.AQA
the neutron: A particle sitting in the nucleus alongside the protons, with a relative mass of 1 and no charge.AQA
The newton as the SI unit of force: Force is measured in newtons, N, and one newton is the force needed to give a 1 kg mass an acceleration of 1 m s⁻².AQA
the normal: The line drawn at 90° to the surface where the ray strikes.AQA
The pascal as newtons per square metre: The unit of pressure, where 1 Pa = 1 N/m², so a force of 60 N over 0.03 m² gives 2000 Pa.OCR
The relationship p = hρg: The pressure at a point is given by p = hρg, where h is depth, ρ is density and g is gravitational field strength.OCR
the Sun as our star: The Sun is the one star within our solar system and the only object in it that gives out its own light.AQA
The wide frequency range of the electromagnetic spectrum: The radiation linked to atomic and nuclear changes may come from any part of the electromagnetic spectrum.OCR
there and back distance: In the recorded time the pulse has covered twice the depth, so the distance to the boundary is (v × t) / 2.AQA
thermal conductivity: A property of a material: brick and glass conduct more readily than foam, mineral wool or trapped air, so a lower value gives a lower rate of energy transfer.AQA, OCR
Thermal Energy: The internal energy present in a system due to its temperature.AQA
Thermal energy change: Calculated as mass in kilograms multiplied by specific heat capacity in J/kg °C multiplied by change in temperature in °C, giving joules.OCR
Thermal energy for a change of state: The mass in kilograms multiplied by the specific latent heat in joules per kilogram, giving an answer in joules.OCR
thermal energy store: The store into which the work done by the brakes transfers energy, so that the brakes get hot.AQA
Thermal equilibrium and temperature change: When the rates of absorption and emission are equal, the temperature stays constant; otherwise the temperature rises or falls.OCR
thermal insulation: A material such as a fibreglass jacket around a hot water tank lowers the thermal conductivity and cuts the rate at which energy passes to the surroundings.AQA, OCR
thermal store: An accepted name for the store that increases when a substance is heated, alongside internal store.AQA
thermal store of the surroundings: Energy is usually dissipated into this store, causing the surroundings to heat up.AQA
thermistor: A resistor whose resistance depends strongly on its temperature: warm it and the resistance falls, cool it and the resistance rises.AQA
thickness monitoring: A thickness gauge for aluminium sheet uses beta, because alpha would be absorbed completely and gamma would pass straight through, so only beta gives a…AQA
Thickness of walls: Greater thickness slows the rate of energy transfer, so the building cools more slowly.OCR
thinking distance: The distance the vehicle travels during the driver's reaction time, when the brakes are not yet on and it carries on at its original steady speed.AQA, OCR
Thomson's plum-pudding model: Atoms contain small negative electrons embedded in a spread of positive charge, often pictured as a plum-pudding model.OCR
three-core cable: A cable containing three separately insulated copper wires, live, neutral and earth, inside one flexible outer sheath.AQA
thunder and lightning: Light arrives effectively instantly, so the delay between the flash and the bang is the sound's travel time.AQA
time distance shielding: Three controls that protect people nearby: reduce time, increase distance and add shielding.AQA
time from half-lives: Worked out by multiplying the number of half-lives by the half-life, giving the final value with the correct unit.AQA
time of use: How long the appliance is switched on for, which together with the power of the appliance determines the amount of energy transferred.AQA
Time taken for energy transfer: A device with a larger power transfers the same energy in less time.OCR
timeline of models: The order to remember is solid sphere, plum pudding, nuclear model, Bohr's fixed orbits, the subdivision of nuclear charge into protons, and finally the…AQA
tip to tail construction: Drawing the first force to length and direction, then drawing the second starting from the tip of the first, keeping its own direction.AQA
tiredness: One of the factors that can affect a driver's reaction time, making the brain take longer to process the hazard and send the signal to the muscles.AQA
Torque: A turning force or moment that causes rotation.Pearson Edexcel
Total distance and total time: The distances of each stage added together and the times of each stage added together, used for the whole journey.OCR
total distance over total time: The calculation of average speed, using totals for both the distance and the time.AQA
Total energy input: The energy supplied to a transfer, which is treated as the total input rather than adding wasted energy to the useful energy.OCR
Total input energy transfer: The energy supplied to the device or process, measured in joules (J).AQA
total internal reflection: The process by which visible light travels through optical fibres.AQA
total resistance: Adding resistors in series increases it, so the current falls, while bringing a second heating element into parallel makes it fall, so the current from the…AQA
towards the normal: The way a wave bends when it slows down, for example going from air into glass.AQA
Tracers and imaging of internal organs: A small amount of a gamma-emitting tracer is taken into the body and its radiation passes out through tissue to a detector, so an image shows where the tracer…OCR
Transfer between GPE and kinetic energy: When an object falls, the stored gravitational potential energy transfers to kinetic energy, so the same equation can find the energy released.OCR
Transfer of electrons between surfaces: Friction moves electrons from one surface to the other, so one surface gains electrons and becomes negatively charged while the other loses electrons and…OCR
transformer: A device in the national grid that sets the voltage, either raising it at the power station or lowering it near homes.OCR
transformer efficiency: Transformers themselves are very efficient, typically above 99%, so little is lost in making the change.AQA
Transformer power relationship: Potential difference across primary coil multiplied by current in primary coil equals potential difference across secondary coil multiplied by current in…OCR
Transformer turns ratio: The number of turns in the primary coil divided by the number of turns in the secondary coil, equal to the ratio of the two coil voltages.OCR
translucent materials: Materials that transmit light but scatter it as it passes, so directions are jumbled and only a blur is seen.AQA
transmission: Some electromagnetic waves pass through materials, such as microwaves passing easily through the atmosphere to reach satellites or X-rays passing through flesh.AQA, OCR
Transmission and reception of radio signals: A transmitting circuit drives charges to and fro to radiate, and a receiving circuit responds to passing radio waves by developing its own small oscillation.OCR
transmission efficiency: Useful output energy transfer divided by total input energy transfer, which is what efficiency measures.AQA
Transmission through space without a medium: They do not need a medium, so they are transmitted through space, a vacuum.OCR
Transmission, absorption and reflection: Effects seen when electromagnetic waves meet a material, such as light passing through, a beam reflecting or a surface warming.OCR
transmitting moments: Taking a turning effect in at one place and delivering it at another, usually with a different size of force.AQA
transparent materials: Materials that transmit light with almost no scattering, so rays keep their directions and a sharp image can be seen through them.AQA
transport: One of the uses of energy resources, alongside electricity generation and heating.AQA
transport speeds: Sensible estimates such as a car on a main road at about 13-30 m/s, a train at about 50 m/s and a passenger aircraft at about 250 m/s.AQA
Transverse nature of electromagnetic waves: Their oscillations are perpendicular to the direction in which the wave travels.OCR
transverse wave: A wave in which the oscillations are perpendicular to the direction of energy transfer, as shown by ripples on a water surface.AQA, OCR
transverse waves: Waves modelled by ripples on a water surface, where the surface moves up and down while the ripple travels along, so the oscillation is perpendicular to the…AQA, OCR
travel through a vacuum: Electromagnetic waves need no particles, so they can travel through a vacuum, which is how energy from the Sun reaches the Earth.AQA
travels through liquids: Because both solids and liquids resist being compressed, these waves travel through solid rock and through the liquid outer core.AQA
tuning a receiver: The receiver circuit is tuned so that it responds strongly to one particular frequency, which is how one station is picked out from the many arriving at once.AQA
turbine and generator: The steam turns a turbine, which turns a generator.AQA
turning effect: What a couple produces, and it is greatest when the plane of the coil lies along the field and falls to zero when the coil is at right angles to it.AQA
Turning effect direction: Whether the turning effect is clockwise or anticlockwise, decided from where the force acts and the direction in which it acts.OCR
Turns ratio and coil arrangement: More secondary turns means step-up, fewer secondary turns means step-down, linking each transformer type to its coil turns.OCR
Turns ratio and power equations: The turns rule states Vₚ ÷ Vₛ = nₚ ÷ nₛ, and the power rule assumes 100% efficiency, meaning power in equals power out (Vₚ × Iₚ = Vₛ × Iₛ).AQA
twenty year gap: The evidence for the neutron did not arrive until about twenty years after the nucleus became an accepted scientific idea.AQA
two branches: The two routes that separate after the main sequence, which should be sketched as a flow chart and learned as a pair.AQA
two conservation totals: The mass numbers across the equation and the atomic numbers across the equation, which are the two totals you balance and nothing else.AQA
two or three neutrons: Released alongside the two smaller nuclei when the nucleus undergoing fission splits.AQA
two reversals per revolution of a coil: A coil spinning steadily in a fixed field gives a potential difference that reverses twice per turn, because each side swaps from moving up through the field…AQA
type of radiation: One of the two main factors the risk of harm from electromagnetic radiation depends on, with different types causing different effects.AQA
Types of nuclear radiation: Alpha particles, beta particles and gamma rays, which differ in charge, mass and nature.OCR
typical appliance powers: Plausible ratings worth learning for a lamp, a television, a kettle and a shower, so an example can always be quoted.AQA
typical reaction times: Values that range from 0.2 s to 0.9 s, varying from person to person.AQA
typical speeds: Values for a person walking, running and cycling, and for different types of transportation systems, that students should be able to recall.AQA
Typical values: Human reaction times are around 0.2 s to 0.3 s, with the ruler dropping roughly 20 cm to 45 cm.OCR

U

UK mains: An example of an alternating voltage supply, at 50 Hz.OCR
ultraviolet: Radiation from the Sun that you cannot tell is present by looking, so sunburn can happen on a cool or overcast day.AQA
ultraviolet absorption: When ultraviolet waves reach humans, they are absorbed by the outer layers of the skin.AQA
Ultraviolet effects on skin and eyes: Mostly absorbed by the skin and eyes, so overexposure can burn the skin, damage the eyes and raise the long-term risk of skin cancer.OCR
unchanged mass number: One neutron has gone but one proton has appeared, so the total is unchanged and the mass number stays the same.AQA
uncontrolled chain reaction: A chain reaction in which more than one neutron from each fission goes on to cause a further fission, so the number of fissions doubles or triples with every…AQA
undeviated central ray: A ray through the centre of the lens that carries straight on without being deviated.AQA
undisturbed position: The rest position of the medium from which displacement is measured out to a crest or down to a trough.AQA
unfamiliar contexts: Situations that are the same physics in new clothes, answered with the same four moves: find the conductor, find the magnetic field, say what is changing,…AQA
Uniform acceleration: Motion in which speed changes at a steady rate, so distance = average speed × time, where average speed = (initial speed + final speed) ÷ 2.AQA, OCR
Uniform acceleration in a straight line: The motion to which the equation linking the change in the square of velocity to acceleration and distance applies.AQA
Uniform density assumption: Treating the atmosphere as having constant density, which is a simplification of the real gradual thinning of air and makes the simple calculation possible.OCR
uniform field: A field that has the same strength and the same direction everywhere in that region.AQA
Uniform motion: Motion in which speed stays constant, so distance = speed × time, rearranged as speed = distance ÷ time or time = distance ÷ speed.OCR
Uniform velocity and balanced forces: If the forces balance, the resultant is zero and the object continues at uniform velocity, or stays at rest.OCR
Unit consistency: Keeping mass and volume in matching units, for example g and cm³ give g/cm³, and converting to kg/m³ by multiplying by 1000.AQA, OCR
Unit consistency and conversion: Convert grams to kilograms and cm/s or km/h to m/s before substituting, then attach the correct unit.OCR
Unit consistency and conversion between cm and m: Keep units consistent by converting centimetres to metres, dividing by 100, so 5 cm becomes 0.05 m.OCR
Unit consistency in calculations: Potential differences are given in volts and turns as plain counts when values are substituted.OCR
Unit consistency in energy calculations: Keep mass in kilograms, specific heat capacity in J/(kg °C) and state the answer in joules or kilojoules consistently.OCR
Unit consistency in gas calculations: Pressure is kept in pascals and volume in cubic metres, converting volumes to m³ first, so the constant has consistent units.OCR
Unit consistency of m²/s²: Both (m/s)² and m/s² × m give m²/s², so both sides of the equation carry the same unit.OCR
unit conversion: Changing values into the right units before substituting, such as converting energy from kilojoules into joules and lengths into metres.AQA, OCR
Unit conversion and calculation: Convert depths to metres and densities to kg/m³ before multiplying, and keep units consistent throughout so the pressure comes out in pascals.OCR
Unit conversion before calculation: Convert centimetres to metres and kilonewtons to newtons before multiplying to avoid unit errors.OCR
Unit conversion before substitution: Convert grams to kilograms by dividing by 1000, and convert km/h to m/s by dividing by 3.6 before squaring.OCR
Unit conversion between cm³ and m³: Converting a volume in cm³ to m³ by dividing by 1 000 000 before substituting into the density equation.OCR
Unit conversion between m/s and km/h: Converting to km/h by multiplying by 3.6, applying the factor to every conversion.OCR
Unit conversion of area to square metres: Areas must be converted to square metres first, using the factor 1 × 10⁻⁴, so that 250 cm² becomes 0.025 m².OCR
Unit conversion of distance to metres: Convert distances to metres first, for example 35 cm = 0.35 m.OCR
Unit conversion of time: Always convert time to seconds first, for example 3 minutes is 180 s and 0.5 minutes is 30 s.OCR
unit equivalence: One newton-metre is one joule, so the numbers do not change and no conversion factor is multiplied or divided.AQA
Unit equivalence between newton-metres and joules: One newton-metre equals one joule, so the numerical value stays unchanged when converting.OCR
unit J/kg: The unit of specific latent heat, written as J/kg with no degrees in it.AQA
unit kg m/s: The unit of momentum, kilograms metre per second, with no division sign anywhere in it.AQA
Unit pairing: Each quantity must be kept in its matching pair: watts with seconds give joules, and kilowatts with hours give kilowatt-hours.OCR
Unit relationship: One watt equals one joule per second, so power is stated in watts rather than joules.OCR
Units and quantities: Power is measured in watts, potential difference in volts and current in amperes.OCR
units J/kg °C: The units of specific heat capacity, joules per kilogram per degree Celsius.AQA
units N, kg and N/kg: Weight, W, is in newtons, N; mass, m, is in kilograms, kg; and gravitational field strength, g, is in newtons per kilogram, N/kg.AQA
Units of acceleration: Follow from the division of velocity by time: (m/s) ÷ s = m/s².OCR
Units of current, potential difference and resistance: Current is measured in amperes (A), potential difference in volts (V) and resistance in ohms (Ω).OCR
units of density: Kilograms per cubic metre, kg/m³, since density is mass divided by volume.AQA, OCR
unknown force: The force found by rearranging the moment equation when the other three quantities are known.AQA
unlike charges attract: A positive object and a negative object pull towards each other along the line joining them.AQA
unlike poles: A north pole and a south pole attract each other.AQA
unpredictable individual nuclei: An old nucleus is no more likely to go than a fresh one, so you cannot say when a given nucleus will decay.AQA
unstable nuclei: Some atomic nuclei are unstable and give out radiation as they change to become more stable.AQA
Unwanted energy transfers: Transfers that waste input energy, mainly by heating, friction and sound, which can be reduced without reducing the useful output.AQA
upright and diminished: For a concave lens the image is always upright and always smaller than the object.AQA
Upthrust and weight balance: An object floats when the upthrust on it balances its weight, and sinks when its weight exceeds the maximum upthrust the fluid can supply.OCR
uranium and plutonium: Heavy nuclei used as fuels whose nuclei hold so many protons and neutrons that they are only just held together.AQA
Useful and wasted energy: The energy transferred usefully by a device is the useful output, while the remaining energy is wasted, often transferred by heating.AQA
Useful and wasted energy in motors: A motor transfers energy electrically to kinetic energy of the moving parts, but friction in bearings and resistance heating in the coils waste energy as…OCR
Useful energy output: The energy delivered by a transfer that is wanted, selected before dividing by the total energy input.OCR
Useful output: Found by multiplying efficiency by total input, and it can never exceed total input for a real device.AQA
Useful output energy transfer: The energy transferred to the intended useful store or pathway, measured in joules (J).AQA
Useful versus less useful energy stores: Energy dispersed over a large area at a low temperature is stored in a less useful way and cannot easily be harnessed to do useful work again.OCR
Useful versus wasted energy: The remaining energy that is not useful output is dissipated to the surroundings, usually by heating.OCR
uses in devices: Its switchability makes it useful in devices like relays, electric bells, circuit breakers, and scrapyard cranes, where a load must be picked up and then…AQA
uses of radiation: Applying knowledge of penetration, ionising power and half-life to match a source to a job such as a smoke alarm, a thickness gauge or a medical tracer.AQA
Using and rearranging equations: Applying power equals potential difference multiplied by current, and rearranging it so that potential difference equals power divided by current and current…OCR
Using standard units and interpreting signs: Velocity is in metres per second, acceleration in m/s² and distance in metres, and a negative value of v² − u² indicates deceleration.AQA
using supplied data: Answering from the figures provided in the question rather than from memory.AQA
using supplied values: Using the value of g given in the question rather than a remembered one, since any value needed will be supplied.AQA
Using V = I × R: The relationships are summarised by this equation, so a 6 V supply across a 3 Ω resistor gives 2 A.OCR

V

V ÷ I at several points: Working out V ÷ I at two points on a graph and comparing the values to see whether the resistance is constant.AQA
V–I characteristic graphs: A straight line through the origin shows constant resistance, while a curved graph shows resistance that changes as current changes.OCR
Value of one square: The velocity represented by one square's height multiplied by the time represented by one square's width.AQA
variable resistor: A variable resistor in series lets you change the current, and so the potential difference across the component under test.AQA
variation between people: Because values vary so much between people, a class set of results should be reported as a mean together with the range.AQA
varying speed: A changing speed through a journey, as when people walk, run or travel in a car.AQA
varying the potential difference: Adjust the variable resistor, or change the number of cells or the supply setting, to get several pairs of readings.AQA
Vector: A quantity that has both magnitude and direction, so a force is fully described only when its size in newtons and its direction are given.OCR
Vector diagrams: Drawings that use arrows to a stated scale to show magnitude and direction, used to illustrate resolution of forces, a net force and equilibrium situations.OCR
Vector directions and reversals: Reversing the current reverses the force, and reversing the field also reverses it.OCR
Vector nature of acceleration: Speeding up, slowing down or changing direction all involve acceleration, so it is a vector.AQA
Vector nature of momentum: Because velocity carries direction, momentum does too, so the direction of the velocity is kept with the momentum.OCR
vector quantity: A quantity that has direction, so an object moving left has momentum in the opposite sense to one moving right.AQA, OCR
vectors: Quantities that need both a size and a direction before they are fully described, and that combine by geometry rather than by simple addition.AQA
vehicle mass: A greater mass means more kinetic energy at the same speed, so a loaded lorry sits above a car on such a graph.AQA
Vehicle safety features: Crumple zones, seat belts and airbags are designed to extend the stopping time, spreading the same change in velocity over a longer time to reduce the force.AQA, OCR
Velocity: A vector quantity, meaning it has both size and direction, so it can be positive or negative depending on the chosen positive direction.AQA, OCR
velocity = frequency × wavelength: The relationship used to link the three quantities and to show how a change in velocity at constant frequency changes wavelength.OCR
Velocity and distance relationships: Final velocity squared minus initial velocity squared equals two times acceleration times distance, useful when time is not given.AQA
Velocity as a vector: A quantity with both a size (speed) and a direction, so a change of direction means a change of velocity.OCR
Velocity change: Found by subtracting the initial velocity from the final velocity, in metres per second (m/s).AQA
Velocity change over time: Acceleration is found using a = (v − u) ÷ t, where u is initial velocity, v is final velocity and t is the time taken.OCR
velocity-time graph: A graph on which the slope gives acceleration: a horizontal line means constant velocity, a rising line means acceleration and a falling line means…AQA, OCR
Velocity-time graph interpretation: The velocity axis is vertical and time is horizontal, and the enclosed area is found by splitting the region between the plotted line and the time axis into…OCR
Velocity–acceleration–distance relationship: The equation states that the square of the final velocity minus the square of the initial velocity equals twice the acceleration multiplied by the distance.OCR
Velocity–time graph: A graph that plots velocity on the vertical axis against time on the horizontal axis.AQA
Velocity–time graph gradients: Acceleration is the gradient, so a straight rising line shows constant positive acceleration and a horizontal line shows zero acceleration.AQA
vertical height: The vertical distance moved, measured in metres, rather than the distance travelled along a slope.AQA
very high reverse resistance: The property of a diode in the reverse direction, which means the current stays at effectively zero however far the potential difference is turned up.AQA
vibration of solids: The conversion of sound waves to vibrations of solids works over a limited frequency range.AQA
virtual image: Where the reflected rays appear to meet behind the mirror, as far behind the mirror as the object is in front.AQA
visible light: The narrow band of electromagnetic waves that our eyes detect, roughly violet to red.AQA
Visible light band: A narrow band of wavelengths, roughly 400 nm to 700 nm, sitting between infrared and ultraviolet.OCR
visible spectrum: The narrow slice of the electromagnetic spectrum the eye detects, running from about 400 nm at the violet end to about 700 nm at the red end.AQA
voltage: A term that may be used instead of potential difference and still gain full credit.AQA
Voltage of the UK mains supply: The stated voltage is about 230 V; the word 'about' matters because the actual value drifts slightly around that figure.OCR
Voltmeter: Goes in parallel across the component being tested.OCR
voltmeter in parallel: The voltmeter is connected in parallel across the component alone, so the potential difference it reads is the one across the component.AQA
voltmeter placement: A voltmeter always goes in parallel across the component, because it compares the potential at two points.AQA
volume displaced: A solid object pushed right under displaces its own volume, so the upthrust is the weight of that volume of fluid.AQA

W

W = F s: The equation linking work done, force and distance, with W in joules, F in newtons and s in metres measured along the direction of the force.AQA
W = m × g: The equation used to calculate the weight of an object, where weight = mass × gravitational field strength.AQA, OCR
wall thickness: For the same material, a thicker wall means a lower rate of energy transfer, so the building cools more slowly.AQA
waste storage: High-level waste from power stations is buried, stored in cooling ponds, sealed in metal containers, encased in concrete or transported in secure vessels.AQA
wasted energy: Energy that is dissipated and stored in less useful ways, becoming so thinly spread that it cannot be usefully recovered.AQA
Wasted energy and the efficiency ratio: Each measure reduces the wasted energy for the same useful output, so the ratio of useful output to total input increases.OCR
Wasted energy in heating devices: A heating device wastes energy by heating the device body and the surrounding air as well as the intended object.OCR
Wasted energy or power: Calculated as the difference between total input and useful output.AQA
Wasted power: The difference between total power input and useful power output, often transferred to the thermal store of the surroundings.AQA
water ripples: An example of a transverse wave in which the water surface moves up and down about its undisturbed level while the ripple travels horizontally outwards.AQA
Wave equation: v = f × λ relates frequency and wavelength, where for EM waves in a vacuum v is the speed of light.OCR
wave fronts: A set of parallel lines, each one a crest, travelling at right angles to the fronts.AQA
wave speed: The speed at which the energy is transferred (or the wave moves) through the medium.AQA, OCR
wave speed in a vacuum: Every colour travels at the same speed in a vacuum, about 3 × 10⁸ m/s, so wave speed = frequency × wavelength fixes the frequency band once the wavelength…AQA
Wave transfers energy not matter: A wave transfers energy from one place to another without transferring the medium itself.OCR
Wave velocity: Equals frequency multiplied by wavelength, written v = f × λ, and is found by multiplying the two quantities.OCR
wavelength: The distance between two matching points on consecutive waves, such as from one crest to the next crest, measured in metres (m).AQA, OCR
Wavelength and energy: What the practical uses of each region of the electromagnetic spectrum depend on.OCR
Wavelength and frequency relationship: Because speed equals frequency multiplied by wavelength, a wave with a longer wavelength must have a lower frequency when the speed is fixed.OCR
wavelength bands: Each colour occupies its own band of wavelengths rather than a single value, and the bands run continuously into one another.AQA
wavelength change: Since wave speed = frequency × wavelength, holding the frequency fixed forces the wavelength to change in the same ratio as the speed.AQA
wavelength dependence: The shares of a wave that are reflected, transmitted and absorbed depend on the material and on the wavelength.AQA
Wavelength distribution depends on temperature: A cool object emits most strongly at long infrared wavelengths, while a hotter object peaks at shorter wavelengths.OCR
Waves in fluids and solids: Waves behave differently in fluids (liquids and gases) and in solids, and their interaction with matter can be observed and measured.OCR
weaker field: Moving away from a charged object means the field strength decreases, and the field the spreading lines represent is more dilute.AQA
Weaker field further from the wire: The field is strongest close to the conductor and weaker further away, because strength decreases as distance increases.OCR
weighing benefit and risk: Setting the benefit against the risk using the figures you are given, rather than listing them separately.AQA
Weight: A force measured in newtons that depends on gravitational field strength, unlike inertial mass, which is a property of the object.AQA, OCR
weight and upthrust: In a liquid, upthrust is not negligible, so the initial resultant force is weight minus upthrust, making initial acceleration less than g.AQA
Weight as gravitational force: The gravitational force on a mass, measured in newtons.OCR
weight depends on location: A force that depends on where the object is, because the gravitational field strength at that point changes.AQA
weight from mass: A mass in kilograms must not be used as the force; it has to be turned into its weight in newtons first.AQA
weight of air: The total downward force from the air molecules above a surface, which decreases as the height of the surface above ground level increases.AQA
Weight of air column: A reduced amount of air above a point means a smaller weight of air column pressing down.OCR
Weight of fluid displaced: Upthrust equals the weight of fluid displaced, so the volume displaced sets the maximum upthrust available.OCR
wet and icy conditions: Adverse road conditions that reduce friction between the tyres and the road.AQA
what each object orbits: The object at the centre of the orbit, which separates the three types: planets orbit the Sun, moons orbit planets and artificial satellites orbit the Earth…AQA
where rays meet: The image is the place where the refracted rays, or their backward projections, meet.AQA
white dwarf and black dwarf: The Sun-like star contracts into a white dwarf, which then cools into a black dwarf.AQA
white surfaces: A surface that reflects all the visible wavelengths about equally, so the mixture leaving it is the same mixture that arrived.AQA
whole-number multiples: The charge of every nucleus is a whole-number multiple of one fixed basic amount, never one and a half times it, never a fraction.AQA
why activity falls: The number of decays per second is proportional to how many undecayed nuclei are left, so as the sample runs down the decays slow down and the curve gets…AQA
wide frequency range: Because the energy changes available range from very small to very large, the frequencies generated and absorbed cover a very wide range.AQA
work against friction: Work done against the frictional forces acting on an object causes a rise in the temperature of the object.AQA
work done: Calculated with W = F × s, where force is in newtons and distance moved in metres along the line of action of that force, giving the answer in joules (J).AQA, OCR
work done against friction: The work done by the friction force between the brakes and the wheel, which reduces the kinetic energy of the vehicle.AQA
work done against gravity: Work done = force × distance, and for a weight lifted the work done is weight × height with no extra step for g.AQA
work done against the force: You must do work against the opposition, and it is the work you do that ends up as electrical energy in the circuit.AQA
work done by a force: Calculated as W = F × s, where F is the force in newtons and s the distance moved along the force in metres, giving joules.OCR
Work done by forces: An object accelerated by a constant force has work done on it, so its kinetic store grows while the force's source store empties.AQA, OCR
work done equals energy stored: Provided the spring is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal.AQA
Work done in stretching: Equals the area under the force–extension graph, and in linear cases is W = ½Fx, where F is the final force and x the extension.OCR
Work done on a gas: Doing work on a gas transfers energy to it, for example when a moving piston compresses the gas.OCR
work done on a spring: The result of a force moving the end of a spring through a distance against the spring's force.AQA
work equation: Work done equals force multiplied by distance moved along the line of action of the force, written W = F s.AQA
worn brakes: Brakes whose worn pads cannot press on the disc as firmly, so braking force falls.AQA
worn brakes and tyres: Poor vehicle condition in which worn tyres have shallow tread and worn brake pads or discs grip the wheel less firmly.AQA
worn tyres: Tyres that cannot channel water away, so the tyre rides on a film of water and friction drops.AQA

Other terms

1000 mSv equals 1 Sv: The conversion is the ordinary milli prefix, so 1000 mSv = 1 Sv.AQA
20 Hz to 20 kHz: The range of normal human hearing, running from about 20 Hz to 20 kHz.AQA
20 kHz: 20 000 Hz, and the highest frequency a person with normal hearing can detect.AQA
230 V supply: The UK domestic supply is about 230 V, the figure to quote whenever a question involves a plug, a socket or a household appliance.AQA

Where these terms come from

Each definition is one we publish on a Physics GCSE topic page or study guide. Open a term to see how each exam board words it and which topic it belongs to. For the full course, go to Physics revision or the glossary for every subject.

Revise Physics with these terms

Create a free account to practise exam questions and get feedback on your answers.

Start free

A week of Premium from your first lesson · Then the free plan continues · No card, no charge

Physics topics

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

Other terms

Where these terms come from

Revise Physics with these terms

Cookies on MasteryMind