O Level Physics: Electromagnetic Spectrum — Practice Questions (Cambridge 5054)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

Related: Waves study guide and Waves revision notes

The electromagnetic spectrum is syllabus section 3.3 of Cambridge O Level Physics (5054), syllabus for 2026, 2027 and 2028. You must know the seven regions in order of frequency and wavelength, know that all electromagnetic waves travel at 3.0 x 10^8 m/s in a vacuum (and approximately the same in air), describe the uses listed for each region, and describe the damage electromagnetic radiation can cause. These questions cover all four learning outcomes, and the calculations combine them with the wave equation v = f x wavelength from section 3.1. Sound, light and general wave properties are practised in the Waves practice questions.

What does syllabus section 3.3 cover?

Outcome	You must be able to
3.3.1	Recall the main regions in order of frequency and of wavelength
3.3.2	Recall that electromagnetic waves travel at 3.0 x 10^8 m/s in a vacuum and approximately the same speed in air
3.3.3	Describe the role of radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays in the listed applications
3.3.4	Describe damage from excessive exposure (heating of soft tissue, burns) and ionising effects of ultraviolet, X-rays and gamma rays

Questions

1. List the seven regions of the electromagnetic spectrum in order of increasing frequency. [2]

2. State two properties shared by all electromagnetic waves. [2]

3. State which region of the electromagnetic spectrum has the longest wavelength, and which has the highest frequency. [2]

4. A local radio station broadcasts at a frequency of 98.0 MHz.

(a) Calculate the wavelength of the radio waves. [3] (b) State the speed of these waves in air, and explain your answer. [2]

5. A microwave oven uses microwaves with a wavelength of 12.2 cm. Calculate their frequency. [3]

6. A television signal is sent from a ground station to a satellite 36 000 km above the Earth. Calculate the time it takes for the signal to reach the satellite. [3]

7. Light takes 500 s to travel from the Sun to the Earth. Calculate the distance from the Sun to the Earth. [2]

8. An X-ray has a wavelength of 1.0 x 10^-10 m. Calculate its frequency. [2]

9. For each application, name the region of the electromagnetic spectrum used.

Application	Region
(a) Remote control for a television
(b) Sterilising drinking water
(c) Mobile (cell) phone signals
(d) Sterilising surgical instruments sealed in packaging
(e) Thermal imaging camera used by firefighters
(f) Checking a passenger’s bag at an airport
(g) Detecting counterfeit bank notes
(h) Studying distant galaxies with a large dish telescope

[8]

10. Explain how ultraviolet radiation is used in security marking of valuable property. [2]

11. Explain why gamma rays, rather than ultraviolet, are used to sterilise food in sealed packets. [2]

12. Both X-rays and gamma rays can be used to detect cracks in metal. Describe how such a crack can be detected. [2]

13. Describe the harmful effects of:

(a) excessive exposure to infrared radiation; [1] (b) ultraviolet radiation; [2] (c) X-rays and gamma rays. [2]

14. Explain why a hospital radiographer stands behind a screen when taking X-ray images, but the patient does not need to. [2]

Answers

1. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays [2]. (1 mark if one pair is in the wrong order.)

2. Any two [1 each]: they all travel at the same speed in a vacuum (3.0 x 10^8 m/s); they are all transverse waves; they can all travel through a vacuum; they all obey v = f x wavelength; they can all be reflected and refracted.

3. Longest wavelength: radio waves [1]. Highest frequency: gamma rays [1].

4. (a) v = f x wavelength, so wavelength = v / f [1] = (3.0 x 10^8) / (98.0 x 10^6) [1] = 3.06 m (3.1 m to 2 significant figures) [1]. (b) Approximately 3.0 x 10^8 m/s [1], because electromagnetic waves travel at approximately the same speed in air as in a vacuum [1].

5. Wavelength = 12.2 cm = 0.122 m [1]; f = v / wavelength = (3.0 x 10^8) / 0.122 [1] = 2.46 x 10^9 Hz (2.5 GHz) [1].

6. Distance = 36 000 km = 3.6 x 10^7 m [1]; time = distance / speed = (3.6 x 10^7) / (3.0 x 10^8) [1] = 0.12 s [1].

7. Distance = speed x time = 3.0 x 10^8 x 500 [1] = 1.5 x 10^11 m [1].

8. f = v / wavelength = (3.0 x 10^8) / (1.0 x 10^-10) [1] = 3.0 x 10^18 Hz [1].

9. [1 each] (a) infrared; (b) ultraviolet; (c) microwaves; (d) gamma rays; (e) infrared; (f) X-rays; (g) ultraviolet; (h) radio waves.

10. The property is marked with ink that is invisible in visible light [1]; under an ultraviolet lamp the ink fluoresces (glows), revealing the owner’s mark [1].

11. Gamma rays are very penetrating, so they pass through the packaging and the food [1] and kill bacteria inside; ultraviolet is absorbed at the surface / cannot pass through the packaging [1].

12. The radiation is passed through the metal and detected (on film or a detector) on the other side [1]; more radiation passes through where there is a crack, so the crack shows up as a different (darker) region [1].

13. (a) Heating of soft tissue / burns to the skin [1]. (b) It is ionising [1]; it can cause skin cancer and cataracts (damage to the eyes) [1]. (c) They are ionising and can damage cells [1], causing cell mutation and cancer [1].

14. The radiographer takes many images every day, so their total exposure would be large [1]; the patient is exposed only briefly and occasionally, so the benefit of the image outweighs the small risk [1].

Where marks are usually lost

• Reversing the order, or putting infrared and ultraviolet the wrong way round.
• Not converting MHz or GHz to Hz, cm to m, or km to m before using v = f x wavelength.
• Giving the speed of electromagnetic waves in air as the speed of sound (about 340 m/s).
• Calling infrared or microwaves ionising.
• Naming a region without saying what it does in the application when the question says “describe”.

Frequently asked questions

Do I need to learn the wavelength of each region? The syllabus asks for the order of regions by frequency and wavelength, not precise values. Learn the order and use values given in questions.

Which regions are ionising in the 5054 syllabus? Ultraviolet, X-rays and gamma rays. Infrared and microwaves cause heating of soft tissue at high exposure.

Is the speed of light in air exactly 3.0 x 10^8 m/s? It is very slightly less, but the syllabus says to treat it as approximately the same as in a vacuum.

Official syllabus

Cambridge O Level Physics (5054) syllabus for examination in 2026, 2027 and 2028, Topic 3 Waves, section 3.3 Electromagnetic spectrum, published by Cambridge International Education.