O Level Physics: Waves — 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.

Most questions practise a skill tested in the June 2025 Paper 22. After each answer there is a tip and, where a paper question matches the skill, the real question to try next.

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Questions

1. A loudspeaker cone vibrates and sends a sound wave through the air to a listener. Describe how the air particles move as the sound wave passes, and name the type of wave. [3]

2. A microphone connected to an oscilloscope picks up a steady note from a whistle. The screen shows exactly 6 complete waves across a time of 0.020 s. (a) State what is meant by the frequency of a wave. (b) Calculate the frequency of the note. (c) Calculate the period of the wave. [3]

3. A guitar string is plucked near a microphone connected to an oscilloscope. The oscilloscope settings are not changed during the experiment. (a) As the note dies away, the height of the trace gets smaller. What change does a listener hear? (b) A second string then plays a note of twice the frequency with the same loudness. State how the sound heard differs, and how the trace on the screen differs. [3]

4. A radio playing in a kitchen can be heard by someone in the hall, around the side of an open doorway, even though they cannot see the radio. (a) Name the process that allows the sound to spread around the edge of the doorway. (b) The speed of sound in air is 340 m/s. Calculate the wavelength of a 340 Hz note from the radio. (c) The doorway is 0.9 m wide. Use your answer to (b) to explain why sound spreads out a lot through the doorway but light does not noticeably spread. [4]

5. A ship sends a pulse of sound straight down to the sea bed. The echo is detected 0.12 s after the pulse is sent. The speed of sound in sea water is 1500 m/s. Calculate the depth of the sea below the ship. [3]

6. A ray of light travels from air into a glass block. The angle of incidence is 40° and the refractive index of the glass is 1.5. (a) Calculate the angle of refraction. (b) State what happens to the speed of the light as it enters the glass. [3]

7. The glass in an optical fibre has a refractive index of 1.5. (a) Calculate the critical angle for this glass. (b) State the two conditions needed for total internal reflection to happen. [3]

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Answers

1. The particles vibrate backwards and forwards about fixed positions [1], parallel to the direction the wave travels (along the line from speaker to listener) [1]; they do not travel with the wave. It is a longitudinal wave, made of compressions and rarefactions [1].

Tip: “backwards and forwards” alone is not enough; say the vibration is along the direction of travel, and that particles do not move from source to listener.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 4.

2. (a) The number of complete waves (oscillations) per second [1]. (b) f = 6 ÷ 0.020 = 300 Hz [1]. (c) T = 1 ÷ f = 1 ÷ 300 = 0.0033 s (3.3 ms) [1].

Tip: count complete waves carefully, then divide by the time they take; frequency and period are reciprocals of each other.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 4.

3. (a) The sound becomes quieter (the amplitude falls) [1]. (b) The note has a higher pitch [1]; the trace has the same height but twice as many waves across the screen (each wave is half as wide) [1].

Tip: amplitude links to loudness and frequency links to pitch; do not mix them up, and if the settings are unchanged, doubling the frequency doubles the number of waves on the screen.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 4.

4. (a) Diffraction [1]. (b) λ = v ÷ f = 340 ÷ 340 = 1.0 m [1]. (c) The sound’s wavelength (about 1 m) is similar to the width of the doorway, so it diffracts strongly [1]. Light has a wavelength of less than a millionth of a metre, far smaller than the gap, so its diffraction is too small to notice [1].

Tip: diffraction is greatest when the gap is about the same size as the wavelength; compare the two sizes directly in your answer.

Try the real question next: Cambridge O Level Physics 5054, June 2025, Paper 22, Question 4.

5. Distance travelled by the pulse = speed × time = 1500 × 0.12 = 180 m [1]. This is there and back [1], so depth = 180 ÷ 2 = 90 m [1].

Tip: an echo travels to the reflector and back, so always halve the total distance.

6. (a) n = sin i ÷ sin r, so sin r = sin 40° ÷ 1.5 = 0.429 [1]; r = 25° (25.4°) [1]. (b) The light slows down [1].

Tip: check your calculator is in degrees, and check the refracted angle is smaller than 40°, because light bends towards the normal when it slows down.

7. (a) sin c = 1 ÷ n = 1 ÷ 1.5 = 0.667, so c = 42° (41.8°) [1]. (b) The light must be travelling from the optically denser medium (glass, higher refractive index) towards the less dense medium (air) [1], and the angle of incidence must be greater than the critical angle [1].

Tip: both conditions are needed; the angle is measured from the normal, not from the surface.

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Where marks are usually lost

• Describing sound particles as moving “up and down”, which describes a transverse wave.
• Mixing up loudness (amplitude) with pitch (frequency).
• Forgetting to halve the distance in echo calculations.
• Saying a gap “must be smaller than the wavelength” instead of comparing sizes for strong diffraction.
• Using the angle to the surface rather than to the normal in refraction calculations.