Properties of electromagnetic waves 2 — AQA GCSE Combined Science
Test yourself on Properties of electromagnetic waves 2 with AQA GCSE practice questions.
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Properties of electromagnetic waves 2 explained
Radio waves are electromagnetic waves with the longest wavelengths and lowest frequencies.
Read the full explanation
In a metal conductor, such as an aerial, electrons can be made to oscillate. When electrons oscillate, they generate radio waves. An alternating potential difference applied to an aerial drives electrons back and forth at the frequency of the supply, producing radio waves of that exact frequency. This principle underlies radio, television and mobile phone communication. Higher Tier students must describe this process in terms of oscillating charges and alternating current, relating the frequency of the electrical oscillation to the frequency of the emitted radio wave.
(HT only) When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit.
This Higher Tier concept links radio waves to electric circuits. When a radio wave is absorbed by a conductor, it pushes electrons back and forth. That motion is an alternating current whose frequency matches the wave. For example, a 100 MHz radio wave absorbed by an aerial drives electrons at 100 million cycles per second, so the induced current alternates at 100 MHz. The same process works in reverse: an alternating current in a conductor radiates radio waves. This is how aerials both receive and transmit. Absorption therefore converts wave energy into electrical energy, and the frequency is preserved.
Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range. Gamma rays originate from changes in the nucleus of an atom.
Electromagnetic waves are produced when energy levels in atoms or nuclei change. In an atom, electrons dropping to lower energy levels emit visible or ultraviolet light, while absorption occurs when electrons jump to higher levels. In the nucleus, rearrangements of protons and neutrons release energy as gamma rays. For example, after alpha or beta decay, a nucleus may be left in an excited state and emit a gamma ray as it settles. Gamma rays have the highest frequencies and shortest wavelengths in the electromagnetic spectrum. The key idea is that the size of the energy change determines the frequency: large nuclear energy changes give gamma rays, smaller atomic energy changes give lower-frequency waves.
Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue. The effects depend on the type of radiation and the size of the dose. Radiation dose (in sieverts) is a measure of the risk of harm resulting from an exposure of the body to the radiation.
Ultraviolet waves, X-rays and gamma rays sit at the high-frequency end of the electromagnetic spectrum and can have hazardous effects on human body tissue. The harm caused depends on the type of radiation and on the size of the dose received. Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer. Radiation dose, measured in sieverts (Sv), is a measure of the risk of harm resulting from an exposure of the body to the radiation. A larger dose means a greater risk of harm. For example, a dental X-ray gives a very small dose, whereas a large dose of gamma radiation can cause acute illness.
1000 millisieverts (mSv) = 1 sievert (Sv)
Radiation dose is measured in sieverts (Sv), but many everyday exposures are much smaller than one sievert, so the millisievert (mSv) is used. The prefix milli- means one thousandth, so 1 mSv is 0.001 Sv and 1000 mSv make 1 Sv. To convert millisieverts to sieverts, divide by 1000; to convert sieverts to millisieverts, multiply by 1000. For example, a dose of 2500 mSv is 2.5 Sv, and a dose of 0.04 Sv is 40 mSv. Being able to convert between these units lets you compare doses of ultraviolet, X-ray or gamma radiation fairly when judging the risk of harm to body tissue.
Students should be able to draw conclusions from given data about the risks and consequences of exposure to radiation.
This skill requires you to interpret data, such as tables or graphs of dose against cancer incidence, and reach a justified conclusion about the risks and consequences of radiation exposure. Risks include an increased chance of cancer or genetic damage; consequences include cell death, tissue damage, radiation sickness at high doses and long-term health effects. A strong answer identifies the pattern in the data, quotes specific values, and links them to a biological effect. For example, if a graph shows that cancer incidence rises from 20 cases per 10 000 people at 5 mSv to 40 cases per 10 000 people at 20 mSv, you can conclude that a fourfold increase in dose is associated with a doubling of cancer incidence, while noting that the data show a correlation and do not by themselves prove causation.
Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.
Ultraviolet (UV) waves carry enough energy to damage skin: they break down collagen and elastin, so skin loses elasticity and ages prematurely, and they damage DNA in skin cells, increasing the risk of skin cancer. X-rays and gamma rays are even more energetic and are ionising: when they pass through living cells they can knock electrons from atoms and molecules, forming ions. This ionisation can alter DNA, causing gene mutations. Mutations may disrupt how a cell divides and grows, so the cell can divide uncontrollably and form a cancer. A concrete example is a radiographer who leaves the X-ray room during exposures and stands behind a lead screen; lead absorbs X-rays, reducing the dose received. Similarly, gamma rays from a radioactive tracer are used in small controlled doses, while workers use shielding and distance to limit exposure.
Your focus
- Describe how oscillations in an electrical circuit produce radio waves.
- Explain the link between the frequency of an alternating current and the frequency of the emitted radio wave.
- Apply the idea of oscillating charges to a simple communication device such as an aerial.
Show all 21 objectives
- Describe how absorbing a radio wave can create an alternating current in a conductor.
- Explain why the induced alternating current has the same frequency as the absorbed radio wave.
- Link induced electrical oscillations to the operation of a radio receiver tuned to the wave frequency.
- State that changes in atoms and nuclei can generate or absorb electromagnetic waves.
- Explain that gamma rays originate from changes in the nucleus of an atom.
- Relate the wide frequency range of electromagnetic waves to different energy changes in atoms and nuclei.
- State that ultraviolet waves, X-rays and gamma rays can harm human body tissue.
- Explain that the effect depends on the type of radiation and the size of the dose.
- Define radiation dose in sieverts as a measure of the risk of harm from exposure.
- State the relationship 1000 mSv = 1 Sv.
- Convert a dose given in millisieverts to sieverts, and vice versa.
- Compare radiation doses accurately by using a consistent unit.
- Interpret a table or graph of radiation dose and health outcome to identify the overall trend.
- Support a conclusion about radiation risk with specific numerical evidence from the data.
- Distinguish between a correlation shown by data and a proven cause-and-effect relationship.
- State the effects of ultraviolet waves on skin, including premature ageing and increased skin cancer risk.
- Explain why X-rays and gamma rays are ionising and how ionisation can mutate genes.
- Describe how exposure to X-rays and gamma rays can be reduced using shielding, distance and time limits.
Properties of electromagnetic waves 2 exam tips
Marking Points
- States that radio waves are produced when charges (electrons) oscillate in an electrical circuit.
- Explains that an alternating potential difference or alternating current causes electrons to oscillate at a particular frequency.
- Relates the frequency of the electrical oscillation to the frequency of the emitted radio wave.
- Applies the idea to a communication context, such as radio broadcasting or mobile phones.
- States that absorption of a radio wave by a conductor transfers energy to electrons in that conductor.
- Explains that the absorbed wave causes electrons to oscillate, producing an alternating current.
- Identifies that the frequency of the induced alternating current equals the frequency of the absorbed radio wave.
- Recognises that the process is reversible: an alternating current in a conductor can generate radio waves.
- Changes in atoms can generate or absorb electromagnetic waves, such as visible light or ultraviolet.
- Changes in atomic nuclei can generate or absorb electromagnetic waves, typically gamma rays.
- Electromagnetic waves are produced over a wide range of frequencies because energy changes vary in size.
- Gamma rays originate from changes in the nucleus of an atom, for example after radioactive decay.
- The frequency of the emitted wave is related to the size of the energy change in the atom or nucleus.
- Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue.
- The effects depend on the type of radiation and the size of the dose.
- Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer.
- X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.
- Radiation dose is measured in sieverts (Sv) and is a measure of the risk of harm from exposure of the body to radiation.
- The sievert (Sv) is the unit of radiation dose.
- The millisievert (mSv) is a smaller unit of radiation dose, equal to one thousandth of a sievert.
- 1000 mSv = 1 Sv, so 1 mSv = 0.001 Sv.
- To convert mSv to Sv, divide the value in mSv by 1000.
- To convert Sv to mSv, multiply the value in Sv by 1000.
- Converting units allows doses to be compared on the same scale when assessing risk of harm.
- Describe the trend shown by the data, such as an increase in cancer incidence as radiation dose increases.
- Quote specific numerical values from the data to support the conclusion, including units where given.
- Link the data pattern to a named risk, such as an increased chance of cancer, or to a consequence, such as cell death or tissue damage.
- Recognise that data show correlation and that other factors may contribute, so causation should not be assumed without further evidence.
- Compare different groups, doses or time periods in the data and state which carries the greater risk.
- Use the conclusion to comment on safety measures, such as limiting exposure time, increasing distance or using shielding.
- Ultraviolet waves can cause skin to age prematurely, for example by damaging collagen and elastin so the skin loses elasticity and develops wrinkles.
- Ultraviolet waves increase the risk of skin cancer because they damage DNA in skin cells.
- X-rays and gamma rays are ionising radiation: they carry enough energy to remove electrons from atoms or molecules, forming ions.
- Ionisation can cause mutation of genes because it changes the DNA base sequence in a cell.
- Mutations in genes that control cell division can lead to uncontrolled cell division and the formation of a cancer.
- The risk from X-rays and gamma rays is reduced by limiting exposure time, increasing distance and using absorbing shielding such as lead.
Examiner Tips
- 💡Use the phrase 'oscillating charges' or 'oscillating electrons' when explaining how radio waves are produced.
- 💡Make clear that the frequency of the emitted radio wave equals the frequency of the alternating current in the circuit.
- 💡State clearly that the frequency of the alternating current is the same as the frequency of the radio wave.
- 💡Use the term 'oscillations' when describing electron motion in the conductor.
- 💡Name the part of the atom responsible for gamma rays: the nucleus.
- 💡Use the phrase 'changes in energy levels' when explaining how electromagnetic waves are generated or absorbed.
- 💡Link the wide frequency range to the different sizes of energy changes in atoms and nuclei.
- 💡Link each radiation to its specific effect on body tissue, such as ultraviolet causing premature skin aging and skin cancer.
- 💡When comparing risks, refer to both the type of radiation and the size of the dose, because the statement requires both factors.
- 💡Write the conversion factor 1000 mSv = 1 Sv at the start of a calculation so you do not invert it.
- 💡Check whether the question gives a dose in mSv or Sv, and convert before comparing or calculating risk.
- 💡Give the unit with your answer, and use mSv for small doses and Sv for large doses to keep numbers sensible.
- 💡Start your answer with a clear conclusion, then support it with at least one specific figure from the data.
- 💡Use comparative language such as higher, lower, greater or smaller, and quote the values being compared.
- 💡If the data are uncertain or limited, say so and explain how more evidence would strengthen the conclusion.
- 💡Link each named wave to its effect: UV to premature skin ageing and skin cancer risk; X-rays and gamma rays to ionisation, gene mutation and cancer.
- 💡Use the term ionising correctly by explaining that electrons are removed from atoms or molecules, forming ions.
- 💡When asked about safety, give practical control measures such as lead shielding, shorter exposure time and greater distance rather than saying 'be careful'.
Common Mistakes
- Error: saying radio waves are sound waves. Correction: radio waves are electromagnetic waves and can travel through a vacuum; sound waves are mechanical and need a medium.
- Error: thinking a steady direct current produces radio waves. Correction: a steady current does not produce radio waves; the current must oscillate or change direction, as in an alternating current.
- Error: confusing the frequency of the electrical supply with the speed of the radio wave. Correction: the frequency of oscillation determines the frequency of the radio wave, but all electromagnetic waves travel at the same speed in a vacuum.
- Error: thinking the induced current has a different frequency from the radio wave. Correction: the current alternates at exactly the same frequency as the absorbed wave.
- Error: confusing absorption with reflection. Correction: absorption transfers wave energy into electrical energy in the conductor, whereas reflection redirects the wave.
- Error: assuming the speed of the wave changes the frequency. Correction: the frequency of the induced current is determined solely by the frequency of the incoming radio wave.
- Saying gamma rays come from electron transitions; correction: gamma rays originate from changes in the nucleus, while electron transitions produce lower-frequency waves such as visible or ultraviolet.
- Thinking all electromagnetic waves come from the same part of the atom; correction: different parts (electron shells versus nucleus) produce different frequency ranges.
- Confusing absorption with emission; correction: absorption occurs when energy is taken in to raise an energy level, while emission occurs when energy is released as a wave.
- Treating all three radiations as having the exact same effect: correct this by stating that UV affects the skin (aging, cancer), whereas X-rays and gamma rays are ionising and can cause gene mutation.
- Confusing dose with the amount of energy alone: correct this by explaining that dose in sieverts measures the risk of harm from exposure.
- Assuming ultraviolet is highly ionising like X-rays: correct this by distinguishing UV's effects on skin from the ionising nature of X-rays and gamma rays which cause gene mutations.
- Multiplying by 1000 when converting mSv to Sv: correct this by dividing by 1000, because 1 mSv is smaller than 1 Sv.
- Writing 1000 Sv = 1 mSv: correct this by remembering that the millisievert is the smaller unit, so 1000 mSv = 1 Sv.
- Ignoring the unit when comparing doses: correct this by converting all values to the same unit, usually Sv or mSv, before comparing.
- Stating that radiation definitely causes cancer in an individual because the data show a correlation. Correction: the data show a statistical association across a population, not proof that a particular person's cancer was caused by the exposure.
- Describing the data without drawing a conclusion, for example listing every value in a table. Correction: select the key pattern and use only the figures that support your conclusion.
- Confusing risk with consequence. Correction: risk is the probability or chance of harm occurring, while consequence is the harm itself, such as tissue damage or cancer.
- Saying UV is ionising like X-rays and gamma rays. Correction: UV can damage skin and DNA, but X-rays and gamma rays are described as ionising radiation in this specification.
- Confusing mutation with immediate burning. Correction: premature ageing and cancer risk are long-term effects of UV damage, not the same as a short-term sunburn.
- Writing that X-rays and gamma rays only harm people who work with them. Correction: any exposure carries some risk, so medical doses are kept as low as reasonably practicable and shielding is used.