Edexcel IGCSE Physics: Waves — Practice Questions

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

Related: Waves revision notes

---

Section A

1. State whether sound is a transverse or a longitudinal wave. [1]

2. State the equation linking wave speed, frequency and wavelength. [1]

3. State what happens to the pitch of a source’s sound as it moves away from a stationary observer, and name the effect responsible. [2]

---

Section B

4. A water wave has a frequency of 4.0 Hz and a wavelength of 0.50 m.

(a) Calculate the speed of the wave. [2] (b) Calculate the time period of the wave. [2]

5. A ray of light travels from air into a glass block, striking the surface at an angle of incidence of 50°. The angle of refraction is measured as 30°.

(a) Calculate the refractive index of the glass. [2] (b) Calculate the critical angle of the glass. [2] (c) State what would happen to a ray inside the glass striking the same surface at an angle of incidence greater than the critical angle. [2]

6. State two uses of infrared radiation and one hazard associated with excessive exposure to it. [3]

7. An oscilloscope connected to a microphone displays a sound wave. A second, louder sound of the same pitch is then made into the microphone.

(a) Describe how the trace on the oscilloscope screen would change between the two sounds. [2] (b) Explain your answer in terms of the physical quantity that has changed. [2] (c) State what would change on the display if the pitch, rather than the loudness, of the sound increased instead. [1]

---

Section C

8. An ambulance approaches a stationary observer with its siren sounding, passes the observer, and then moves away.

(a) Describe how the pitch heard by the observer changes throughout this sequence. [2] (b) Explain, in terms of wavefronts, why the pitch changes as it does both as the ambulance approaches and as it recedes. [4]

9. A student is given an unlabelled block of transparent material and measures a critical angle of 39° for it using a ray-tracing method.

(a) Calculate the refractive index of the material. [2] (b) Explain, using the idea of total internal reflection, how the student could use this material to redirect a beam of light through 90° without losing light to absorption at a reflecting surface. [3] (c) Explain why this design is used in binoculars and periscopes instead of ordinary mirrors. [2]

---

Worked answers

1. Longitudinal. [1]

2. v = f λ. [1]

3. The pitch falls (gets lower); the Doppler effect. [2]

4. (a) v = f λ = 4.0 x 0.50 = 2.0 m/s. [2] (b) T = 1/f = 1/4.0 = 0.25 s. [2]

5. (a) n = sin i / sin r = sin 50°/sin 30° = 0.766/0.500 = 1.53 (3 s.f.). [2] (b) sin c = 1/n = 1/1.53 = 0.654, so c = 40.9° (1 d.p.). [2] (c) It would undergo total internal reflection rather than refracting out of the glass. [2]

6. Any two uses (e.g. thermal/night-vision imaging, remote controls, short-range wireless data links); hazard: skin burns from excessive exposure. [3]

7. (a) The trace would show the same spacing between peaks (same frequency/wavelength on screen) but a greater height (larger amplitude). [2] (b) Loudness corresponds to amplitude, so a louder sound of the same pitch has a larger amplitude but an unchanged frequency, which is why the peak spacing (representing frequency) stays the same while the trace’s height (representing amplitude) increases. [2] (c) The peaks would be spaced closer together (representing a higher frequency), rather than the trace’s height changing. [1]

8. (a) The pitch is higher than the siren’s true pitch as the ambulance approaches, drops sharply at the moment it passes, and is lower than the true pitch as it recedes. [2] (b) As the ambulance approaches, each successive sound wavefront is emitted from a position closer to the observer than the previous one, so the wavefronts arrive bunched closer together, shortening the observed wavelength and raising the observed frequency (pitch). As the ambulance moves away, each wavefront is emitted from further back, so wavefronts arrive more spread out, lengthening the observed wavelength and lowering the observed frequency (pitch). [4]

9. (a) n = 1/sin c = 1/sin 39° = 1/0.629 = 1.59 (3 s.f.). [2] (b) A 45° prism made from the material can be arranged so the light strikes one internal face at 45°, which is greater than the material’s 39° critical angle, so instead of refracting out, the light undergoes total internal reflection off that internal face and is redirected through 90° while remaining inside the prism. [3] (c) Total internal reflection reflects effectively all of the incident light with no absorption loss at the reflecting surface, whereas an ordinary mirror’s silvered coating absorbs and scatters a small but significant fraction of the light at every reflection, so a prism-based design keeps the image brighter, especially after several internal reflections in an instrument like a periscope or binoculars. [2]

Official syllabus

Pearson Education Ltd, Pearson Edexcel International GCSE in Physics (4PH1) Specification, Issue 4 — the same specification cited by the Waves study guide and its revision notes. Always check the current specification for your examination year.