Properties and hazards of electromagnetic waves - Teacher Slides.pptx

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Properties and hazards of electromagnetic waves

Waves

Lesson 8 of 12

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Warm-up

Waves

Lesson 8 of 12

Answer each one, then check.

1

What is ionising radiation?

2

What is an alternating current?

3

Where do gamma rays come from?

4

What is a mutation?

5

What is radiation dose measured in?

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Warm-up - Answers

Waves

Lesson 8 of 12

1

What is ionising radiation?

Radiation that can remove electrons from atoms

2

What is an alternating current?

A current that changes direction repeatedly

3

Where do gamma rays come from?

The nucleus of an atom

4

What is a mutation?

A change in the DNA of a cell

5

What is radiation dose measured in?

Sieverts (Sv)

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Learning Objectives

Waves

Lesson 8 of 12

1

Explain that changes in atoms and nuclei can produce and absorb electromagnetic waves.

2

Explain how radio waves are produced and detected (Higher tier).

3

Describe the hazardous effects of ultraviolet, X-rays and gamma rays.

4

Use data on radiation dose to draw conclusions about risk.

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Waves

Lesson 8 of 12

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.

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Radio Waves: Producing and Detecting (Higher)

Waves

Lesson 8 of 12

The received current has the same frequency as the wave.

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Hazards of Electromagnetic Waves

Waves

Lesson 8 of 12

Higher frequency waves carry more energy and can ionise.

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Hazards

Waves

Lesson 8 of 12

Learn the effects.

Radiation

Hazardous effect

Ultraviolet

Premature skin ageing; increased risk of skin cancer; eye damage

X-rays

Ionising: can mutate genes and cause cancer

Gamma rays

Ionising: can mutate genes and cause cancer

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Producing Radio Waves (Higher)

Waves

Lesson 8 of 12

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

1

Transmitter

Oscillations (an alternating current) in an electrical circuit produce radio waves

2

Receiver

When radio waves are absorbed by an aerial, they create an alternating current in the circuit

3

Frequency

The current has the same frequency as the radio wave

ANSWER

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

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Risk and Dose

Waves

Lesson 8 of 12

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

1

Ratio

7 ÷ 0.02 = 350

2

Comparison

The CT scan gives 350 times the dose

ANSWER

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

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Sources of EM Waves

Waves

Lesson 8 of 12

Explain where gamma rays come from.

1

Nucleus

An unstable nucleus changes to become more stable

2

Emission

It emits gamma radiation

3

Atoms

Changes in electron energy levels produce other parts of the spectrum

ANSWER

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

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Dose

Waves

Lesson 8 of 12

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.

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Key Terms

Waves

Lesson 8 of 12

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.

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Waves

Lesson 8 of 12

YOUR TASK

Compare the Doses

10 minutes

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.

WHAT A GOOD ANSWER SHOWS

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

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Can I...?

Waves

Lesson 8 of 12

Explain how gamma rays are produced.

Explain how radio waves are produced.

Explain how radio waves are detected.

Name hazards of UV.

Name hazards of X-rays.

Define radiation dose.

Compare doses.

Draw conclusions from data.

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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)

Skin cancer or premature skin ageing.

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Exam Practice: Properties and hazards of electromagnetic waves

Waves

Lesson 8 of 12

Answer all questions. Use the mark allocation as a guide to how much to write. · 14 minutes

Question 1 · 2 marks · State

Give two hazards of exposure to ultraviolet radiation.

Question 2 · 3 marks · Explain

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

Question 3 · 4 marks · Use the chart

The chart shows the radiation dose a patient receives from different medical procedures. (a) Which procedure gives the greatest dose? (b)…

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Exam Practice: Properties and hazards of electromagnetic waves (cont.)

Waves

Lesson 8 of 12

Question 4 · 3 marks · Explain

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

Question 5 · 1 mark · State

State where gamma rays originate.

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Question 1 · 2 marks · State

Waves

Lesson 8 of 12

“

Give two hazards of exposure to ultraviolet radiation.

HOW TO ANSWER IT

Command word: State. Worth 2 marks, so plan before writing.

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Question 1 · mark scheme

Waves

Lesson 8 of 12

2 marks available. Award a mark for each point made.

First hazard

1 mark

Second hazard

1 mark

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Question 2 · 3 marks · Explain

Waves

Lesson 8 of 12

“

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

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 2 · mark scheme

Waves

Lesson 8 of 12

3 marks available. Award a mark for each point made.

Ionising: remove electrons

1 mark

Damage or mutate genes or cells

1 mark

Can cause cancer

1 mark

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Question 3 · 4 marks · Use the chart

Waves

Lesson 8 of 12

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. (4 marks)

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Question 3 · mark scheme

Waves

Lesson 8 of 12

4 marks available. Award a mark for each point made.

Chest CT scan

1 mark

7 ÷ 0.02

1 mark

350 times

1 mark

Benefit outweighs risk or more information

1 mark

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Question 4 · 3 marks · Explain

Waves

Lesson 8 of 12

“

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

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 4 · mark scheme

Waves

Lesson 8 of 12

3 marks available. Award a mark for each point made.

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

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Question 5 · 1 mark · State

Waves

Lesson 8 of 12

“

State where gamma rays originate.

HOW TO ANSWER IT

Command word: State. Worth 1 mark, so plan before writing.

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Question 5 · mark scheme

Waves

Lesson 8 of 12

1 mark available. Award a mark for each point made.

The nucleus

1 mark

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