AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER
The electromagnetic spectrum
Waves · Lesson 7 of 12
Teacher copy - includes the notes for whoever is teaching from it.
Warm-up
Answer each one, then check.
1. What is a wave?
A way of transferring energy
2. What is frequency?
Number of waves per second
3. Name a colour of the rainbow.
Red, orange, yellow, green, blue, indigo or violet
4. What is the speed of light in a vacuum?
3.0 × 10⁸ m/s
5. What type of wave is light?
Transverse
Learning Objectives
1. List the seven types of electromagnetic wave in order.
2. State that all EM waves are transverse and travel at the same speed in a vacuum or air.
3. Relate wavelength to frequency across the spectrum.
4. Give examples of energy transfer by EM waves.
The Em Spectrum
Electromagnetic waves are transverse waves that transfer energy from a source to an absorber. They form a continuous spectrum and all travel at the same speed through a vacuum or air.
From long to short wavelength (or low to high frequency): radio, microwave, infrared, visible light (red to violet), ultraviolet, X-rays, gamma rays.
The Electromagnetic Spectrum
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Longer wavelength means lower frequency. |
The electromagnetic spectrum from radio waves to gamma rays with wavelength and frequency trends.
The Seven Groups
Learn the order.
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Group |
Wavelength |
Frequency |
|---|---|---|
|
Radio waves |
Longest |
Lowest |
|
Microwaves |
|
|
|
Infrared |
|
|
|
Visible light (red to violet) |
|
|
|
Ultraviolet |
|
|
|
X-rays |
|
|
|
Gamma rays |
Shortest |
Highest |
Using the Wave Equation
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A radio wave has a frequency of 100 MHz. Calculate its wavelength. Speed of EM waves = 3.0 × 10⁸ m/s. |
1. Convert
100 MHz = 1.0 × 10⁸ Hz
2. Rearrange
λ= v ÷ f
3. Substitute
λ= 3.0 × 10⁸ ÷ 1.0 × 10⁸
4. Answer
λ= 3.0 m
Answer: 3.0 m
Memory Aid
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Give a way to remember the order of the EM spectrum. |
1. Initials
Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma
2. Sentence
Rabbits Mate In Very Unusual eXpensive Gardens
Answer: Use a mnemonic such as 'Rabbits Mate In Very Unusual eXpensive Gardens'.
Energy Transfer
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Give examples that show EM waves transfer energy from a source to an absorber. |
1. Microwaves
Heat food
2. Infrared
Warm your skin from a fire
3. Light
Provides energy to plants and to solar cells
4. Gamma rays
Transfer energy to cells
Answer: Each wave carries energy from its source to an absorber, where it increases a thermal or other energy store.
Key Facts
Remember these.
▸ Transverse. All EM waves are transverse.
▸ Same speed. They all travel at 3.0 × 10⁸ m/s in a vacuum.
▸ Continuous. There are no gaps between the groups.
▸ Our eyes. Detect only visible light, a limited range of the spectrum.
Key Terms
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Electromagnetic wave A transverse wave that can travel through a vacuum. |
Spectrum A continuous range of wavelengths or frequencies. |
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Radio wave The electromagnetic wave with the longest wavelength. |
Gamma ray The electromagnetic wave with the shortest wavelength. |
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Visible light The part of the spectrum our eyes detect. |
Absorber An object that takes in the energy of a wave. |
Your Task: Order the Waves
8 minutes
|
Put these in order of increasing frequency: X-rays, radio waves, visible light, microwaves, gamma rays, infrared, ultraviolet. 1. Use the mnemonic. |
A good answer shows: Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Note: Ask which has the highest energy.
Can I...?
☐ List the EM spectrum in order.
☐ Say they are transverse.
☐ State the common speed.
☐ Link wavelength and frequency.
☐ Use v = fλ for EM waves.
☐ Name the visible colours.
☐ Say eyes detect only visible light.
☐ Give an example of energy transfer.
Summary
✓ Order: radio, microwave, infrared, visible, ultraviolet, X-rays, gamma.
✓ All are transverse and travel at the same speed in a vacuum.
✓ Wavelength decreases as frequency increases.
✓ Eyes detect only visible light.
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EXAM FOCUS List the electromagnetic waves in order of increasing frequency, starting with radio waves. (2 marks) Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. |
Exam Practice: The electromagnetic spectrum
Answer all questions. Use the mark allocation as a guide to how much to write. · 14 minutes
▸ Question 1 · 2 marks · Complete. The electromagnetic spectrum is shown in order of increasing frequency. Radio waves, microwaves, infrared, visible light, ___, X-rays…
▸ Question 2 · 3 marks · Use the diagram. The diagram shows the electromagnetic spectrum with some waves missing. (a) Name the waves labelled A and B. (b) State one property that…
▸ Question 3 · 3 marks · Calculate. A radio wave has a frequency of 100 MHz. The speed of electromagnetic waves in air is 3.0 × 10⁸ m/s. Calculate the wavelength. (1 MHz = 10⁶…
▸ Question 4 · 2 marks · State. State two properties that are the same for all electromagnetic waves.
▸ Question 5 · 3 marks · Explain. Gamma rays have a much higher frequency than radio waves. Explain why their wavelength is much shorter.
Question 1 · 2 marks · Complete
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“The electromagnetic spectrum is shown in order of increasing frequency. Radio waves, microwaves, infrared, visible light, ___, X-rays, gamma rays. Name the missing wave.” |
HOW TO ANSWER IT Command word: Complete. Worth 2 marks, so plan before writing.
Question 1 · mark scheme
2 marks available. Award a mark for each point made.
▸ Ultraviolet. 1 mark
▸ Correct position in order. 1 mark
▸ Model answer. Ultraviolet.
Question 2 · 3 marks · Use the diagram
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The diagram shows the electromagnetic spectrum with some waves missing. (a) Name the waves labelled A and B. (b) State one property that all electromagnetic waves have. (3 marks) |
|
Question 2 · mark scheme
3 marks available. Award a mark for each point made.
▸ A: infrared. 1 mark
▸ B: ultraviolet. 1 mark
▸ A common property. 1 mark
▸ Model answer. (a) A: infrared. B: ultraviolet. (b) They are transverse, or they travel at the same speed in a vacuum.
Question 3 · 3 marks · Calculate
|
“A radio wave has a frequency of 100 MHz. The speed of electromagnetic waves in air is 3.0 × 10⁸ m/s. Calculate the wavelength. (1 MHz = 10⁶ Hz)” |
HOW TO ANSWER IT Command word: Calculate. Worth 3 marks, so plan before writing.
Question 3 · mark scheme
3 marks available. Award a mark for each point made.
▸ Converts to 1.0 × 10⁸ Hz. 1 mark
▸ Correct substitution. 1 mark
▸ 3.0 m. 1 mark
▸ Model answer. λ= 3.0 × 10⁸ ÷ 1.0 × 10⁸ = 3.0 m
Question 4 · 2 marks · State
|
“State two properties that are the same for all electromagnetic waves.” |
HOW TO ANSWER IT Command word: State. Worth 2 marks, so plan before writing.
Question 4 · mark scheme
2 marks available. Award a mark for each point made.
▸ Transverse waves. 1 mark
▸ Same speed in a vacuum. 1 mark
▸ Model answer. They are all transverse. They all travel at the same speed in a vacuum (or air).
Question 5 · 3 marks · Explain
|
“Gamma rays have a much higher frequency than radio waves. Explain why their wavelength is much shorter.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 5 · mark scheme
3 marks available. Award a mark for each point made.
▸ Same speed. 1 mark
▸ v = fλ. 1 mark
▸ Higher frequency means shorter wavelength. 1 mark
▸ Model answer. All electromagnetic waves travel at the same speed in a vacuum. Since v = fλ, a greater frequency means a shorter wavelength.