O Level / IGCSE Physics chapter 3: Waves MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

114 exam-style questions on Waves, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

114 questions · 4 topics · 10 per test

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What chapter 3 covers

Ten Waves questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Which radiation harms the body mainly by heating soft tissue, rather than by ionising it?

  1. A
    gamma rays
  2. B
    microwaves
  3. C
    ultraviolet
  4. D
    X-rays
Show answer

Answer: B. Microwaves are absorbed by the water in tissue and heat it, which can cause burns. Ultraviolet, X-rays and gamma rays are ionising and can cause cell mutation and cancer.

2. An earthquake produces seismic P-waves and S-waves. Which row describes them correctly?

  1. A
    P-waves: transverse; S-waves: longitudinal
  2. B
    P-waves: transverse; S-waves: transverse
  3. C
    P-waves: longitudinal; S-waves: longitudinal
  4. D
    P-waves: longitudinal; S-waves: transverse
Show answer

Answer: D. P-waves (primary) are longitudinal: the ground vibrates along the direction of travel. S-waves (secondary) are transverse: the vibration is at right angles to the direction of travel.

3. A microwave oven uses waves of frequency 2.4 GHz. What is their wavelength? (speed of electromagnetic waves = 3.0 × 108 m/s)

  1. A
    0.0125 m
  2. B
    0.125 m
  3. C
    8.0 m
  4. D
    125 m
Show answer

Answer: B. 2.4 GHz = 2.4 × 109 Hz. λ = v ÷ f = 3.0 × 108 ÷ 2.4 × 109 = 0.125 m. Treating GHz as MHz (106) gives 125 m; dividing f by v gives 8.0.

4. Which list gives colours of the visible spectrum in order of increasing wavelength?

  1. A
    red, orange, yellow, green
  2. B
    violet, blue, green, red
  3. C
    green, blue, indigo, violet
  4. D
    violet, red, green, blue
Show answer

Answer: B. The order of wavelength from longest to shortest is red, orange, yellow, green, blue, indigo, violet, so increasing wavelength runs from violet towards red.

5. Two astronauts stand next to each other on the Moon, where there is no air. With their radios switched off they cannot hear each other speak, but when they press their helmets together they can. Why?

  1. A
    light carries the sound between the helmets
  2. B
    sound travels faster in a vacuum once the helmets touch
  3. C
    pressing the helmets together makes their voices louder
  4. D
    sound can pass through the solid helmets in contact but not through the vacuum
Show answer

Answer: D. Sound needs a medium of particles to pass on the vibrations. The touching helmets form a solid path; the vacuum between separated helmets has no particles, so sound cannot cross it.

6. A student stands 99 m from a tall wall and claps so that each clap is made at the same moment as the echo of the previous clap arrives. A friend times 21 claps (from the 1st to the 21st) and records 12.0 s. What value does this give for the speed of sound?

  1. A
    16.5 m/s
  2. B
    165 m/s
  3. C
    330 m/s
  4. D
    347 m/s
Show answer

Answer: C. 21 claps contain 20 intervals, so one interval = 12.0 ÷ 20 = 0.60 s. In each interval the sound travels 2 × 99 = 198 m, so v = 198 ÷ 0.60 = 330 m/s. Dividing by 21 gives 347 m/s; forgetting the return trip gives 165 m/s.

7. The distance from a crest to the next crest of a wave is 0.60 m and the distance from the rest position to a crest is 0.05 m. What are the wavelength and amplitude?

  1. A
    wavelength 0.60 m, amplitude 0.05 m
  2. B
    wavelength 0.30 m, amplitude 0.10 m
  3. C
    wavelength 0.05 m, amplitude 0.60 m
  4. D
    wavelength 1.20 m, amplitude 0.05 m
Show answer

Answer: A. Wavelength is crest to crest (0.60 m). Amplitude is the maximum displacement from rest (0.05 m), not crest to trough.

8. What is the frequency of a wave?

  1. A
    the distance between two successive crests
  2. B
    the number of wavelengths passing a point per second
  3. C
    the maximum displacement from the rest position
  4. D
    the time for one complete wave
Show answer

Answer: B. Frequency is the number of complete waves (wavelengths) passing a point per unit time, measured in hertz. The time for one wave is the period.

9. Which type of electromagnetic wave is used in remote controllers for televisions and in thermal imaging?

  1. A
    ultraviolet
  2. B
    microwaves
  3. C
    infrared
  4. D
    X-rays
Show answer

Answer: C. Infrared is emitted by warm objects (thermal imaging) and used for short-range remote controls and optical fibres.

10. Water waves pass through a gap in a barrier. The gap is made wider and, at the same time, the frequency of the waves is increased. What happens to the spreading of the waves beyond the gap?

  1. A
    it increases, because the waves now have a longer wavelength
  2. B
    it stays the same, because the two changes cancel out
  3. C
    it increases, because a wider gap lets more waves through
  4. D
    it decreases, as the gap is wider and the wavelength shorter
Show answer

Answer: D. A higher frequency at the same speed means a shorter wavelength (λ = v/f). Diffraction is greatest when the gap is about the same size as the wavelength, so a wider gap and a shorter wavelength both reduce the spreading.

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Ways to practise this chapter

Waves: questions students ask

How many Waves MCQs are there?

114, each with the answer and a short explanation, across 4 topics: General properties of waves, Light, Electromagnetic spectrum, Sound. Every chapter test draws ten of them, so you can take it many times.

Is the O Level / IGCSE Physics chapter 3 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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