IGCSE Physics: Waves — Practice Questions (Cambridge 0625)

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available free from your board.

Related: Waves study guide and revision notes

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Section A

1. A wave has a frequency of 5 Hz and a wavelength of 2 m. Calculate its speed. [2]

2. State whether sound and light are transverse or longitudinal waves, and give one reason for each answer. [2]

3. State the law of reflection. [1]

Section B

4. A ray of light passes from air into a glass block.

(a) State what happens to the speed and direction of the ray as it enters the glass. [2] (b) The angle of incidence is 40° and the angle of refraction is 25°. Calculate the refractive index of the glass. [2]

5. (Supplement) A ray of light inside a glass block strikes the glass-air boundary at an angle greater than the critical angle.

(a) State what happens to the ray. [1] (b) A student claims that a weaker refracted ray still escapes into the air in this situation. Explain why this claim is incorrect. [2]

6. An object is placed between F and 2F of a converging lens.

(a) Describe the image formed (position type, size, orientation, real or virtual). [3] (b) State both parts of the definition of the lens’s principal focus. [2]

7. List the regions of the electromagnetic spectrum in order of increasing frequency, and state one named use of microwaves. [3]

8. An ultrasound pulse is sent from a ship and reflects off the sea floor. The pulse returns after 0.4 seconds, and the speed of sound in water is 1500 m/s.

(a) Calculate the depth of the sea floor below the ship. [2] (b) Explain why the wave equation v = fλ is not used in this calculation. [2]

9. White light passes through a glass prism and disperses into a spectrum. Explain, in terms of refraction, why red and blue light end up separated, and state which colour refracts more. [3]

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Answers

1. v = fλ = 5 × 2 = 10 m/s [2].

2. Sound is longitudinal because the particles of the medium vibrate parallel to the direction the wave travels [1]. Light is transverse because its vibration (the oscillating electric and magnetic fields) is at right angles to the direction of travel [1].

3. The angle of incidence equals the angle of reflection [1].

4. (a) The ray slows down [1] and bends towards the normal [1] (since glass is denser than air). (b) n = sin i / sin r = sin 40° / sin 25° = 0.643 / 0.423 = 1.52 (accept 1.5–1.53) [2].

5. (a) Total internal reflection occurs — the ray reflects entirely back into the glass [1]. (b) Once the angle of incidence exceeds the critical angle, no refracted ray exists at all; the claim incorrectly assumes a weaker refracted ray can still escape, but past the critical angle 100% of the light is reflected internally, with none transmitted into the air [2].

6. (a) The image is real [1], inverted [1], and enlarged, formed beyond 2F on the other side of the lens [1]. (b) The principal focus is the point where rays travelling parallel to the principal axis converge [1], after refraction by the lens [1] — both parts are required for full credit.

7. Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma [2] (full marks for correct order; lose one mark for one error). Named use of microwaves: satellite communication (or mobile phones/Wi-Fi) [1].

8. (a) The pulse travels to the sea floor and back in 0.4 s, so the one-way travel time is 0.2 s [1]. Depth = speed × time = 1500 × 0.2 = 300 m [1]. (b) The wave equation v = fλ relates speed, frequency and wavelength, none of which are given or needed here; this calculation instead uses speed = distance/time, since the quantities available are speed, time, and the distance (depth) being found [2].

9. White light is made up of different colours, each with a different wavelength/frequency, and each colour refracts by a slightly different amount when it passes into and out of the glass prism [1]. Because each colour bends by a different amount, the colours separate out into a visible spectrum after passing through the prism [1]. Blue light refracts more than red light [1].

A note on the ultrasound method

Question 8 uses the standard depth = (speed × time) / 2 method, halving the total travel time because the pulse must travel out to the reflecting surface and back again before being detected. This is a distinct calculation method from the wave equation used elsewhere in this topic, and confusing the two — reaching for v = fλ simply because a question mentions a wave — is one of the most common errors students make on Supplement-tier sound questions. Practise identifying which method a question requires by checking which three quantities (speed, distance, time, or speed, frequency, wavelength) are actually given, rather than defaulting to whichever formula was used most recently in revision, since both calculation methods appear within this same topic and are easy to mix up under time pressure in the exam room.