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Physics · Waves

Properties and hazards of electromagnetic waves

Describe how electromagnetic waves are produced and absorbed, and the hazards of ultraviolet, X-rays and gamma rays, including radiation dose.

  • 6 key terms
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Teacher resources

The teacher copies: slides with the questions built in, the answers, and anything else attached to this lesson for whoever is teaching it.

Student handouts

The same files the students see, to print or hand out.

Warm-up

Answer each one, then check.

  1. 1

    What is ionising radiation?

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    Radiation that can remove electrons from atoms

  2. 2

    What is an alternating current?

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    A current that changes direction repeatedly

  3. 3

    Where do gamma rays come from?

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    The nucleus of an atom

  4. 4

    What is a mutation?

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    A change in the DNA of a cell

  5. 5

    What is radiation dose measured in?

    Show answerHide answer

    Sieverts (Sv)

Learning Objectives

  1. 1Explain that changes in atoms and nuclei can produce and absorb electromagnetic waves.
  2. 2Explain how radio waves are produced and detected (Higher tier).
  3. 3Describe the hazardous effects of ultraviolet, X-rays and gamma rays.
  4. 4Use data on radiation dose to draw conclusions about risk.

PRODUCTION AND HAZARDS

Changes in atoms and in 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.

Ultraviolet, X-rays and gamma rays can have hazardous effects on body tissue. The effects depend on the type of radiation and the size of the dose.

Hazards

Learn the effects.

  • Ultraviolet

    Hazardous effect: Premature skin ageing; increased risk of skin cancer; eye damage

  • X-rays

    Hazardous effect: Ionising: can mutate genes and cause cancer

  • Gamma rays

    Hazardous effect: Ionising: can mutate genes and cause cancer

Producing Radio Waves (Higher)

Explain how radio waves are produced and how they can be detected.

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  1. 1 Transmitter Oscillations (an alternating current) in an electrical circuit produce radio waves
  2. 2 Receiver When radio waves are absorbed by an aerial, they create an alternating current in the circuit
  3. 3 Frequency The current has the same frequency as the radio wave

AnswerAn alternating current produces radio waves; absorbed waves produce an alternating current of the same frequency.

Risk and Dose

A chest X-ray gives a dose of 0.02 mSv and a CT scan of the chest gives 7 mSv. Compare the doses.

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  1. 1 Ratio \(7 \div 0.02 = 350\)
  2. 2 Comparison The CT scan gives 350 times the dose

AnswerThe CT scan gives a dose 350 times greater, so a greater risk.

Sources of EM Waves

Explain where gamma rays come from.

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  1. 1 Nucleus An unstable nucleus changes to become more stable
  2. 2 Emission It emits gamma radiation
  3. 3 Atoms Changes in electron energy levels produce other parts of the spectrum

AnswerGamma rays are emitted by changes in the nucleus of an atom.

Dose

Radiation dose units.

  • Sievert

    Dose is measured in sieverts (Sv); 1000 mSv = 1 Sv.

  • What it shows

    A measure of the risk of harm from exposure.

  • Depends on

    The type of radiation and the size of the dose.

  • No need to recall

    You do not need to recall the unit of dose.

Compare the Doses

A dental X-ray gives 0.005 mSv and a flight from London to New York gives about 0.08 mSv. Calculate how many dental X-rays have the same dose as the flight. Do you think the risk is large?

1. Divide the doses.

2. Comment on the size.

A good answer shows: 0.08 ÷ 0.005 = 16 dental X-rays. Both doses are very small, so the risk is small.

Can I...?

  1. 1Explain how gamma rays are produced.
  2. 2Explain how radio waves are produced.
  3. 3Explain how radio waves are detected.
  4. 4Name hazards of UV.
  5. 5Name hazards of X-rays.
  6. 6Define radiation dose.
  7. 7Compare doses.
  8. 8Draw conclusions from data.

Summary & Exam Focus

  • UV: premature ageing and skin cancer.
  • X-rays and gamma rays: ionising; can mutate genes and cause cancer.
  • Radio waves produced by oscillations in circuits (Higher).
  • Dose measured in sieverts.

Exam focus

State one hazard of exposure to ultraviolet radiation. (1 mark) (1 marks)

Skin cancer or premature skin ageing.

Key terms

The vocabulary this lesson expects you to use. Each one is linked from the first place it appears above.

Ionising radiation
Radiation that can remove electrons from atoms.
Radiation dose
A measure of the risk of harm from exposure to radiation.
Sievert
The unit of radiation dose.
Millisievert
One thousandth of a sievert.
Mutation
A change in the genes of a cell.
Aerial
A device that transmits or receives radio waves.

Questions and answers

10 questions set on this lesson, with the mark schemes and model answers open.

1. Exam question State 2 marks Easier

Give two hazards of exposure to ultraviolet radiation.

Mark scheme — 2 marks available

  • First hazard — 1 mark
  • Second hazard — 1 mark

Model answer

Any two from: premature skin ageing; increased risk of skin cancer; damage to the eyes.

2. Exam question Explain 3 marks Easier

X-rays and gamma rays are described as ionising radiation. Explain why they are a hazard to human health.

Mark scheme — 3 marks available

  • Ionising: remove electrons — 1 mark
  • Damage or mutate genes or cells — 1 mark
  • Can cause cancer — 1 mark

Model answer

They can remove electrons from atoms and damage or mutate the genes in cells, which can lead to cancer.

3. Exam question Use the chart 4 marks Easier

The chart shows the radiation dose a patient receives from different medical procedures. (a) Which procedure gives the greatest dose? (b) Calculate how many times greater the dose from a chest CT scan is than from a chest X-ray. (c) Suggest why a doctor might still use a CT scan.

A bar chart comparing the radiation dose in millisieverts for medical procedures and a flight.

Mark scheme — 4 marks available

  • Chest CT scan — 1 mark
  • 7 ÷ 0.02 — 1 mark
  • 350 times — 1 mark
  • Benefit outweighs risk or more information — 1 mark

Model answer

(a) CT scan of the chest. (b) 7 ÷ 0.02 = 350 times. (c) It gives more detailed information, so the benefit of diagnosis outweighs the small increase in risk.

4. Exam question Explain 3 marks Easier

Explain how radio waves are produced in a transmitter and how they can be detected by a receiver.

Mark scheme — 3 marks available

  • Oscillations in a circuit produce radio waves — 1 mark
  • Waves absorbed by the aerial — 1 mark
  • Produces an alternating current of the same frequency — 1 mark

Model answer

An alternating current (oscillations) in the transmitter circuit produces radio waves of the same frequency. When the radio waves are absorbed by the receiver's aerial they create an alternating current with the same frequency as the wave.

5. Exam question State 1 mark Easier

State where gamma rays originate.

Mark scheme — 1 mark available

  • The nucleus — 1 mark

Model answer

From changes in the nucleus of an atom.

6. Multiple choice 1 mark Easier

A hazard of ultraviolet is...

  1. A skin cancer Correct
  2. B hearing loss
  3. C a cold
  4. D bone growth

Why: UV can damage skin cells.

7. Multiple choice 1 mark Core

Gamma rays come from...

  1. A the Sun's surface only
  2. B the nucleus of an atom Correct
  3. C radios
  4. D lamps

Why: Changes in the nucleus.

8. Multiple choice 1 mark Core

X-rays are...

  1. A harmless
  2. B sound waves
  3. C ionising Correct
  4. D made of electrons

Why: They can ionise atoms.

9. Multiple choice 1 mark Core

Radio waves are produced by...

  1. A friction
  2. B chemical reactions
  3. C falling objects
  4. D oscillations in an electrical circuit Correct

Why: An alternating current.

10. Multiple choice 1 mark Stretch

A dose of 1000 mSv is...

  1. A 1 sievert Correct
  2. B 1 mSv
  3. C 10 Sv
  4. D 0.1 Sv

Why: 1000 milli = 1.