Practise Types of electromagnetic waves. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Electromagnetic (EM) waves are transverse waves that transfer energy from a source to an absorber. You need the order of the EM spectrum by wavelength and frequency, the fact that all EM waves travel at the same speed through a vacuum, and examples of EM waves transferring energy. Expect recall questions and v = f λ calculations.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Name the parts of the EM spectrum in orderRadio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
3
State that EM waves are transverseEM waves are transverse waves that transfer energy from a source to an absorber.
4
Link spectrum position to wavelength and frequencyRadio waves have the longest wavelength and lowest frequency; gamma rays have the shortest wavelength and highest frequency.
5
State that all EM waves travel equally fastAll EM waves travel at the same speed through a vacuum (space) or air: 3.0 × 108 m/s.
5
Give examples of EM waves transferring energyE.g. infrared from a fire warming your skin, or microwaves heating food in an oven.
6
Use v = f λ with standard formE.g. find the wavelength of a 100 MHz radio wave using a speed of 3.0 × 108 m/s.
7
Explain why higher frequency means shorter wavelengthAll EM waves have the same speed, so a higher frequency means a proportionally shorter wavelength.
Notes
What EM waves are
Electromagnetic waves are transverse waves. They transfer energy from the source of the waves to an absorber.
They do not need a medium: they can travel through a vacuum. This is how light from the Sun reaches the Earth.
All EM waves travel at the same speed through a vacuum or air: 3.0 × 108 m/s (300 000 000 m/s). Exam questions normally give you this value.
The electromagnetic spectrum
EM waves form a continuous spectrum: there are no gaps, and each group merges into the next.
In order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
The wavelengths cover a huge range: some radio waves are kilometres long, while gamma rays have wavelengths smaller than an atom.
Visible light runs from red (longest wavelength) to violet (shortest wavelength).
Our eyes only detect visible light, so we can only see a very small part of the spectrum.
Energy transfer and the wave equation
Examples of EM waves transferring energy: infrared and visible light from the Sun warm the Earth; microwaves transfer energy to food in a microwave oven; radio waves transfer energy from a transmitter to the aerial of a radio; X-rays transfer energy to the detector that records an X-ray image.
v = f λ applies to EM waves. Because v is the same for all of them, frequency and wavelength are inversely proportional: double the frequency and the wavelength halves.
So as you go from radio waves to gamma rays, the frequency goes up and the wavelength goes down.
Cheatsheet
EM waves are transverse and transfer energy from a source to an absorber
Frequency increases from radio to gamma; wavelength decreases
All EM waves travel at 3.0 × 108 m/s in a vacuum (and air)
Visible light: red (longest λ) to violet (shortest λ)
Our eyes detect only visible light
v = f λ, so λ = v ÷ f and f = v ÷ λ
1 MHz = 106 Hz; 1 GHz = 109 Hz
How to answer each type of question
Recall: complete the EM spectrum
1 to 3 marks3
Write out the whole spectrum in order in the margin first.
Match each gap to its position.
Example. Some groups of the electromagnetic spectrum are listed in order of increasing frequency. radio waves, microwaves, A, visible light, ultraviolet, B, C Name the groups A, B and C.
Show the model answer
A: infrared (1) B: X-rays (1) C: gamma rays (1)
Compare wavelength, frequency or speed of EM waves
1 to 2 marks4
Higher frequency means shorter wavelength.
In a vacuum or air, the speed is the same for every type.
Example. (a) Which type of electromagnetic wave has the highest frequency? Tick (✓) one box. infrared / microwaves / ultraviolet / X-rays (b) Compare the speed of X-rays in a vacuum with the speed of microwaves in a vacuum.
Show the model answer
(a) X-rays (1) (b) They travel at the same speed (1)
Give an example of energy transfer by EM waves
2 marks5
Name the type of EM wave.
Name the source and the absorber, and say what the energy does.
Example. Give one example of electromagnetic waves transferring energy from a source to an absorber. Name the type of wave, the source and the absorber.
Show the model answer
Infrared (1) from an electric heater is absorbed by a person's skin, which warms up (1).
Calculate the wavelength or frequency of an EM wave
3 marks6
Convert MHz or GHz to Hz using standard form.
Rearrange v = f λ for the unknown.
Use v = 3.0 × 108 m/s (or the value given) and give the unit.
Example. A Wi-Fi router emits microwaves with a frequency of 2.4 GHz. The speed of electromagnetic waves is 3.0 × 108 m/s. Calculate the wavelength of the microwaves.
Show the model answer
2.4 GHz = 2.4 × 109 Hz (1) λ = v ÷ f = 3.0 × 108 ÷ 2.4 × 109 (1) λ = 0.125 m (0.13 m to 2 significant figures) (1)
Shortcuts and memory tricks
Order of the spectrum: 'Rowdy Monkeys In Vans Use X-ray Goggles' (radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma).
Left to right (radio → gamma): frequency up, wavelength down.
Quick anchor: with a speed of 3 × 108 m/s, a frequency of 300 MHz gives a wavelength of exactly 1 m.
Sense check: a microwave wavelength should come out in millimetres or centimetres, and visible light in hundreds of nanometres.
Where marks are lost
Saying different EM waves travel at different speeds in a vacuum.
Getting the order of the spectrum wrong, e.g. putting ultraviolet before visible light, or swapping microwaves and infrared.
Mixing up frequency and wavelength: gamma rays have the highest frequency but the shortest wavelength.
Losing powers of ten when converting MHz or GHz to Hz.
Calling EM waves longitudinal.
Exam technique
Learn the spectrum in order: questions often give part of it and ask you to fill the gaps.
Use the ×10x key for standard form, and give very large or very small answers in standard form.
Use the value of the speed of EM waves given in the question.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Give two examples of electromagnetic waves transferring energy from a source to an absorber.
Any two, e.g. the Sun warming your skin; a microwave oven heating food.
The visible light, X-rays and gamma rays from the explosion all reach a telescope on a satellite at the same time. Explain why.
All electromagnetic waves travel at the same speed through a vacuum.
State what all electromagnetic waves transfer from a source to an absorber.
Energy
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy3 marks
(a) Which list shows the seven types of electromagnetic wave in order of increasing frequency? Tick (✓) one box.[1]
A radio station broadcasts using radio waves with a frequency of 97.5 MHz. The speed of electromagnetic waves in air is 3.0 × 108 m/s.
(a) Calculate the wavelength of the radio waves.[3]
(b) Give two examples of electromagnetic waves transferring energy from a source to an absorber.[2]
(c) Human eyes can only detect a limited range of electromagnetic waves. Name this part of the electromagnetic spectrum.[1]
Show the answer and mark scheme
(a)Answer: 3.1 m (3.08 m) m
97.5 MHz = 9.75 × 107 Hz
λ = 3.0 × 108 ÷ 9.75 × 107
3.1 (m)
(b)Answer: Any two, e.g. the Sun warming your skin; a microwave oven heating food.
infrared / visible light from the Sun warming the Earth or a person's skin
microwaves from a microwave oven heating food
radio waves from a transmitter being absorbed by an aerial
infrared from an electric heater warming a room
light from a lamp being absorbed by a solar cell / the eye
(c)Answer: Visible light
visible light
Question 3Hard8 marks
The speed of electromagnetic waves in a vacuum is 3.0 × 108 m/s.
(a) An X-ray used in a hospital has a wavelength of 1.2 × 10−10 m. Calculate the frequency of the X-ray.[3]
(b) The wavelengths of visible light range from about 4.0 × 10−7 m (violet) to 7.0 × 10−7 m (red). Calculate the range of frequencies of visible light. Give your answers to 2 significant figures.[3]
(c) Calculate how many times greater the frequency of the X-ray is than the frequency of red light.[2]