Physics 0625 · syllabus 3.4
Cambridge IGCSE Physics 0625 — Sound topical past papers
Sound as a longitudinal wave from vibrating sources, the range of human hearing, measuring the speed of sound, loudness and pitch, echoes, and the uses of ultrasound.
- Questions
- 671
- Years
- 2009–2026
- With mark scheme
- 100%
- Questions 2022–2026
- 228
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Sound covers
Sound is made by vibrating objects, such as a loudspeaker cone, a guitar string or the vocal cords, and it travels as a longitudinal wave: the particles of the air vibrate back and forth along the direction the sound travels. Sound needs a medium, so it cannot cross a vacuum. Extended candidates describe the compressions, where the particles are pushed together, and the rarefactions, where they are spread apart, and know that sound is generally fastest in solids, slower in liquids and slowest in gases.
People can hear frequencies from about 20 Hz to 20 000 Hz, and sound travels through air at about 330–350 m/s. A larger amplitude gives a louder sound, and a higher frequency a higher pitch. An echo is sound reflected from a surface. The speed of sound in air is found by timing sound over a measured distance: for example, a partner bangs two blocks together 200 m away and you time the gap between seeing the blocks meet and hearing the bang, then divide the distance by the time.
Ultrasound is sound with a frequency above 20 kHz, too high for people to hear. Extended candidates describe how it is used to find hidden cracks in metal without damaging it, to scan soft tissue such as an unborn baby, and in sonar, where the time a pulse takes to return from the sea bed or a shoal of fish gives its distance: half of the speed multiplied by the time, because the pulse goes there and back.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 3.4 Sound
What you should be able to do
- Describe how sound is produced and explain why it needs a medium
- Describe sound as a longitudinal wave with compressions and rarefactions (Extended)
- Describe a method for measuring the speed of sound in air from a distance and a time
- Relate loudness to amplitude and pitch to frequency, including on traces of sound waves
- Calculate distances from echo times, remembering that the sound travels there and back
- Describe the uses of ultrasound in testing materials, medical scanning and sonar (Extended)
Key ideas
- Sound is longitudinal and needs a medium; it cannot travel through a vacuum
- Human hearing: about 20 Hz to 20 000 Hz; ultrasound is sound above 20 kHz
- Speed of sound in air about 330–350 m/s; generally faster in liquids and faster still in solids (Extended)
- Louder means a larger amplitude; higher pitch means a higher frequency
- Distance to a reflector = speed × echo time ÷ 2
How Sound has been examined
From 2022 to 2026, Sound was on Paper 3 · Theory (Core) in 14 of 14 exam series, worth about 8% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 90 | 7% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 87 | 7% | 14 of 14 |
| Paper 3 · Theory (Core) | 28 | 8% | 14 of 14 |
| Paper 4 · Theory (Extended) | 22 | 7% | 10 of 14 |
| Paper 6 · Alternative to Practical | 1 | 1% | 1 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1. The bank files this topic together with neighbouring ones, so these figures count every question in its chapters, including some on those topics.
Filed in Momentum under: Waves and Sounds.
A worked example
A ship's sonar sends an ultrasound pulse straight down, and the echo from the sea bed returns 0.24 s later. The speed of sound in seawater is 1500 m/s. Find the depth of the water, and say whether a person could hear the sonar if it works at 40 kHz.
- Distance the pulse travels = speed × time = 1500 × 0.24 = 360 m
- The pulse goes down and back up, so the depth = 360 ÷ 2 = 180 m
- 40 kHz = 40 000 Hz, above the upper limit of human hearing, about 20 000 Hz
Answer: 180 m; no, at 40 kHz the sonar is ultrasound
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Forgetting to halve the echo time — the sound travels to the reflector and back, so the distance is half of speed × time
- Linking pitch to amplitude or loudness to frequency — on a trace, taller waves are louder and more tightly packed waves are higher-pitched
- Saying sound travels fastest in air — it is generally slowest in gases, faster in liquids and fastest in solids
- Describing sound as air moving from the source to the listener — the particles vibrate about fixed positions, and it is energy that travels
- Timing sound over a short distance with a hand-held stopwatch — reaction time is then large compared with the time being measured, so use a long distance and repeat the timing
Exam technique
- For a speed-of-sound method, say how the distance is measured, what is timed and with what, that the timing is repeated and averaged, and that speed = distance ÷ time
- On traces drawn to the same scales, compare heights for loudness and the number of waves across the screen for pitch
- Write the formula with the ÷ 2 in it before substituting into any echo or sonar calculation
- Write 20 kHz as 20 000 Hz when comparing it with the range of human hearing
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.