Magnetic fields — AQA GCSE Combined Science
Test yourself on Magnetic fields with AQA GCSE practice questions.
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Magnetic fields explained
A magnetic field is the region around a magnet in which a force can act on another magnet or on a magnetic material.
Read the full explanation
The magnetic materials named in the specification are iron, steel, cobalt and nickel; steel is mostly iron, so it behaves as a magnetic material too. The field is strongest at the poles and becomes weaker with distance. Field lines are drawn from the north pole to the south pole outside the magnet, and the closer together the lines, the stronger the field. A plotting compass placed near a magnet lines up along the field line at that point, so a student can map the field by marking the compass needle direction at several positions and joining the marks with a smooth curve.
The force between a magnet and a magnetic material is always one of attraction.
A magnetic material is one that is attracted towards a magnet, such as iron, steel, cobalt or nickel. Because such a material is not itself a permanent magnet, it has no fixed north or south pole to repel. When it is brought near a magnet, the magnet induces magnetism in it, so the near face always becomes an opposite pole and the two attract. This is why a fridge magnet clings to a steel door and why an iron nail is pulled towards either pole of a bar magnet. Contrast this with two permanent magnets, where like poles repel and unlike poles attract. The key idea is that attraction is the only possible outcome between a magnet and a magnetic material, whatever the orientation of the material.
The strength of the magnetic field depends on the distance from the magnet. The field is strongest at the poles of the magnet.
A magnetic field is the region around a magnet where a magnetic force can be detected. Its strength is not uniform: it is greatest close to the magnet and weaker further away. Around a bar magnet, the field is strongest at the north and south poles, where the field lines are most concentrated, and weaker at the sides and with increasing distance. Field lines are drawn with arrows pointing from north to south outside the magnet, and the spacing of the lines shows strength: closely spaced lines mean a strong field, widely spaced lines mean a weak field. A plotting compass placed near a magnet aligns with the field at that point, so moving the compass traces the field pattern and shows how strength falls with distance.
The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed at that point. The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south(seeking) pole of the magnet.
A magnetic field is a region where a magnetic force can act. To define its direction at a point, imagine placing a tiny free north pole there: the force it feels points along the field. Field lines map this: each line leaves a magnet's north-seeking pole and curves round to enter its south-seeking pole, so the arrow on a line runs N to S outside the magnet. Where lines are close, the field is strong; where they are spread out, it is weak. For example, around a bar magnet the lines form closed loops from N to S outside, and the arrow at any point shows the force direction on a north pole placed there. Inside the magnet the lines continue from S to N, completing the loop.
A magnetic compass contains a small bar magnet. The Earth has a magnetic field. The compass needle points in the direction of the Earth’s magnetic field.
A magnetic compass is a small bar magnet mounted so it can pivot freely. Because a freely suspended magnet aligns with the local magnetic field, the compass needle rotates until it lies along the Earth's magnetic field at that place. The end of the needle that points roughly north is the north-seeking pole; it is attracted towards the Earth's magnetic south-seeking pole, which lies near the geographic north. This is why a compass helps with navigation. The needle does not point exactly to the geographic North Pole because of magnetic declination, and nearby magnets or iron objects can deflect it. For example, holding a compass near a bar magnet makes the needle swing to align with the stronger local field rather than the Earth's field.
describe how to plot the magnetic field pattern of a magnet using a compass
To plot a magnetic field pattern, place a magnet on paper and put a small plotting compass near one pole. Mark the direction the compass needle points, move the compass so its centre is at that mark, and mark the new direction. Repeat this around the magnet to form a line. Crucially, repeat this entire process from different starting points near the pole to draw multiple field lines. Join the marks with smooth lines and add arrows showing the direction from the north to the south pole. The finished pattern shows the field's shape, and the spacing of the lines indicates field strength. Keep the compass away from other magnetic materials to avoid distortion.
draw the magnetic field pattern of a bar magnet showing how strength and direction change from one point to another
A bar magnet produces a three-dimensional magnetic field, but exam answers use a two-dimensional pattern of field lines. Draw lines that leave the north pole and enter the south pole, forming closed loops through the magnet. Direction is shown by arrowheads pointing away from north and towards south. Strength is shown by line spacing: lines are closest together at the poles, where the field is strongest, and spread out with distance, where it is weaker. A plotting compass placed at a point aligns with the local field line, so its north-seeking pole points along the arrow. Field lines never cross, because a compass at a crossing would have two directions at once.
explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic.
A magnetic compass contains a small magnet that is free to rotate. It always settles with its north-seeking pole pointing roughly towards the Earth's geographic north. This happens because the Earth behaves as though a giant bar magnet is inside it, producing a magnetic field that exerts a turning force on the compass needle. The compass aligns with the local field line, so its direction indicates the field direction at that place. Because the needle responds wherever it is used on the Earth's surface, the field must originate within the Earth. The only plausible source is the Earth's core, so the core must be magnetic. The field is not exactly aligned with the rotation axis, which is further evidence that it comes from the core rather than from the Earth's rotation alone.
Your focus
- Define the magnetic field as the region where a magnetic force can act.
- Identify iron, steel, cobalt and nickel as magnetic materials.
- Describe how field lines and a plotting compass represent the direction and relative strength of a magnetic field.
Show all 24 objectives
- Identify iron, steel, cobalt and nickel as magnetic materials.
- Explain why a magnet always attracts a magnetic material.
- Distinguish between the behaviour of a magnetic material and that of a second permanent magnet.
- Describe how magnetic field strength changes with distance from a magnet.
- Identify the poles as the strongest parts of the magnetic field.
- Use field-line spacing and a plotting compass to compare field strength at different points.
- Define the direction of a magnetic field at a point using the force on a north pole.
- Draw and interpret magnetic field lines around a bar magnet with correct arrow directions.
- Use field-line spacing to compare magnetic field strength at different points.
- Describe the structure of a magnetic compass and how it responds to a magnetic field.
- Explain why a compass needle points in the direction of the Earth's magnetic field.
- Predict and explain the effect of a nearby magnet on a compass needle.
- Describe the steps needed to plot a magnetic field pattern with a compass.
- Explain why the compass is moved to each marked point in turn.
- Describe how to add direction arrows to a plotted field pattern.
- Draw the magnetic field pattern around a bar magnet, including direction arrows.
- Use line spacing to represent how field strength changes from point to point.
- Explain how a plotting compass can be used to determine field direction at a chosen point.
- Describe how a magnetic compass behaves in the Earth's magnetic field.
- Use compass behaviour as evidence that the Earth has a magnetic field originating in its core.
- Distinguish between geographic and magnetic poles when explaining compass direction.
Magnetic fields exam tips
Marking Points
- A magnetic field is a region, not a material object, and it exists around every magnet.
- A force acts within the field on another magnet or on a magnetic material.
- The magnetic materials listed are iron, steel, cobalt and nickel.
- Field strength is greatest at the poles and decreases as distance from the magnet increases.
- Field lines run from north to south outside the magnet, and their spacing shows relative field strength.
- State that magnetic materials include iron, steel, cobalt and nickel.
- Explain that a magnetic material is attracted towards a magnet, never repelled.
- Describe how a magnet induces magnetism in a magnetic material, producing an opposite pole on the near face.
- Contrast the behaviour of a magnetic material with that of a second permanent magnet, where like poles repel.
- Apply the idea to a familiar context, such as a fridge magnet holding to a steel door or an iron nail being pulled towards either pole.
- State that magnetic field strength decreases as distance from the magnet increases.
- Identify the poles as the regions where the magnetic field is strongest.
- Interpret field-line diagrams, using line spacing to judge relative field strength.
- Describe how a plotting compass can be used to trace a magnetic field pattern around a magnet.
- Explain that field lines point from north to south outside the magnet and are most concentrated at the poles.
- State that magnetic field direction at a point equals the direction of the force on a free north pole placed at that point.
- Draw field lines with arrows pointing away from the north-seeking pole and towards the south-seeking pole outside the magnet.
- Explain that field lines are a model: the tangent to a line at a point gives the field direction there.
- Use line spacing to compare field strength: closer lines mean a stronger field, wider spacing means a weaker field.
- Describe the field as three-dimensional around a magnet, not confined to the plane of the page.
- Recognise that inside a magnet the field lines run from south-seeking to north-seeking pole, completing closed loops.
- State that a compass contains a small bar magnet that is free to rotate.
- Explain that the Earth itself has a magnetic field, so a freely pivoted magnet aligns with it.
- Describe the compass needle as pointing along the direction of the Earth's magnetic field at its location.
- Identify the north-seeking pole of the compass needle as the end that points towards the Earth's magnetic south-seeking pole near geographic north.
- Explain that a nearby magnet or iron object can produce a stronger local field and deflect the compass needle.
- Recognise that the compass indicates magnetic north, which differs slightly from geographic north due to magnetic declination.
- Place the magnet on paper and place a plotting compass near one pole.
- Mark the direction in which the compass needle points, then move the compass to that mark and repeat to form a line.
- Repeat the process from different starting points near the pole to draw multiple field lines.
- Join the marks with smooth lines and add arrows showing the direction from north to south.
- Keep the compass away from other magnets or magnetic materials to avoid a distorted pattern.
- Field lines are drawn leaving the north pole and entering the south pole, with arrowheads showing that direction.
- Lines form continuous closed loops, returning through the inside of the magnet from south to north.
- Line spacing is used to represent strength: closely spaced lines at the poles show a strong field, wider spacing away from the magnet shows a weaker field.
- The pattern is symmetrical about the magnet's axis, and lines do not cross one another.
- A plotting compass at any point lies along the local field line, with its north-seeking pole pointing in the direction of the arrow.
- A compass needle is a small magnet that is free to rotate and aligns with the local magnetic field.
- The needle consistently points approximately north-south wherever it is used on the Earth's surface.
- This consistent alignment is evidence that the Earth itself produces a magnetic field.
- The Earth's magnetic field must originate from a magnetic core, because the field is present everywhere on the surface.
- The magnetic poles are close to, but not exactly at, the geographic poles, which supports the idea of a magnetic source inside the Earth rather than a rotational effect.
Examiner Tips
- 💡Name all four magnetic materials when the question asks which materials are affected by a magnetic field.
- 💡Use the spacing of field lines to compare field strength, and state that closer lines mean a stronger field.
- 💡When describing a plotting compass method, say that the compass is moved to a new position each time and the needle direction is marked before joining the marks.
- 💡Name the magnetic materials explicitly when asked to give examples, rather than saying 'metal'.
- 💡Use the word 'induced' when explaining why attraction occurs, and link it to the opposite pole formed on the near face.
- 💡If a question describes two objects, decide first whether both are permanent magnets or one is a magnetic material, then apply the correct rule.
- 💡When sketching a field, draw lines closer together near the poles and further apart away from the magnet.
- 💡Use the spacing of field lines as evidence when asked to compare field strength at two points.
- 💡Describe the plotting compass method step by step, including marking the compass direction and joining the marks to show a field line.
- 💡When asked to draw a magnetic field, always add arrowheads and check they point away from N and towards S.
- 💡If asked to compare field strength at two points, refer to the spacing of field lines rather than the length of the lines.
- 💡Use the phrase 'force on a north pole' when defining field direction, as this matches the specification wording closely.
- 💡Link the compass to the idea of a freely suspended bar magnet aligning with a magnetic field.
- 💡When explaining compass direction, mention both the needle's north-seeking pole and the Earth's magnetic south-seeking pole near geographic north.
- 💡If a question mentions a magnet near a compass, explain the deflection in terms of the stronger local field overriding the Earth's field.
- 💡Write the method as a clear sequence of steps, including the repeated move-and-mark step.
- 💡Remember to state that the process must be repeated from different starting points to show the spacing between multiple field lines.
- 💡Mention that the paper, magnet and compass should be kept away from other magnetic materials.
- 💡Use a sharp pencil and draw smooth curves; a ruler is only useful for the straight central axis line.
- 💡Add arrowheads at least once on every line, not just at the poles, so direction is unambiguous.
- 💡Annotate the diagram with 'strong field' near the poles and 'weak field' far away to make the strength change explicit.
- 💡Link each observation to a conclusion: compass behaviour leads to the idea of an Earth-wide field, which leads to a magnetic core.
- 💡Use the phrase 'north-seeking pole' rather than just 'north pole' to avoid ambiguity.
- 💡Mention that the field is present at all locations on the Earth's surface, which rules out a local cause.
Common Mistakes
- Listing only iron as a magnetic material: correct this by including steel, cobalt and nickel as well.
- Drawing field lines from south to north outside the magnet: correct this by drawing them from north to south outside the magnet.
- Treating the field as existing only where a field line is drawn: correct this by stating that the field fills the surrounding space and lines are a model used to represent it.
- Thinking that turning a magnetic material around can make it repel a magnet. Correction: a magnetic material has no fixed poles, so it is always attracted.
- Confusing magnetic materials with permanent magnets. Correction: only a permanent magnet has fixed north and south poles that can repel another magnet.
- Believing that all metals are magnetic. Correction: only iron, steel, cobalt and nickel are magnetic; copper, aluminium and gold are not.
- Assuming the field is the same strength everywhere around a magnet. Correction: the field is strongest at the poles and weakens with distance.
- Thinking that field lines crossing mean a stronger field. Correction: field lines never cross; strength is shown by how closely spaced they are.
- Drawing field lines with arrows pointing from south to north outside the magnet. Correction: outside the magnet, arrows point from north to south.
- Drawing arrows on field lines pointing from south to north outside the magnet; correct this by remembering the convention that outside the magnet lines run from north-seeking to south-seeking pole.
- Treating field lines as paths that a north pole travels along; correct this by explaining that a field line shows direction at each point, not a route.
- Assuming field lines can cross; correct this by stating that at any point the field has one direction, so lines never intersect.
- Saying the compass needle points to the geographic North Pole exactly; correct this by explaining it aligns with the Earth's magnetic field, which is close to but not exactly at geographic north.
- Believing the Earth has a giant bar magnet with its north pole at the geographic north; correct this by stating that the Earth's magnetic south-seeking pole is near geographic north, which is why the compass north-seeking pole is attracted there.
- Thinking the compass needle is attracted to the Earth by gravity or static electricity; correct this by stating it is a magnetic interaction between the needle's magnetic poles and the Earth's magnetic field.
- Moving the compass randomly instead of placing it at the previous mark; correct this by always moving the compass centre to the last marked point.
- Drawing straight lines between marks instead of smooth curves; correct this by joining the marks with a smooth line that follows the field direction.
- Plotting only a single field line; correct this by repeating the method from different starting points to reveal the full field pattern and line spacing.
- Drawing arrowheads pointing from south to north: correct this by remembering that field lines are defined as leaving a north pole and entering a south pole.
- Drawing field lines that cross: correct this by checking that each point in space has only one field direction, so lines must curve apart rather than intersect.
- Showing uniform spacing everywhere: correct this by crowding lines near the poles and spreading them out with distance to represent changing strength.
- Saying the compass is attracted to the geographic North Pole: correct this by explaining that the compass aligns with the Earth's magnetic field, whose south magnetic pole is near geographic north.
- Claiming the compass needle points to the Earth's core: correct this by stating that the needle aligns with the field at its location, and the field's origin is the core.
- Confusing magnetic poles with geographic poles: correct this by noting that the magnetic axis is tilted relative to the rotation axis, so compass north differs slightly from true north.