# A student measures the speed of sound in air by standing a large distance from a tall brick wall and clapping their hands at a steady rhythm until each clap coincides with the echo of the previous clap. Explain how the student can use this method to calculate the speed of sound in air, and state what two quantities must be measured.

> Pearson Edexcel International GCSE Physics (4PH1) — 3.1 Properties of waves · Explain · 4 marks

> The student stands 85 m from the wall and adjusts their clapping rate until each clap perfectly coincides with the returning echo of the previous clap.

## Mark scheme (4 marks)

1. The sound (clap) travels to the wall and is reflected back as an echo, so the total distance travelled by the sound is twice the distance from the student to the wall.
2. The student must measure the distance from the wall.
3. The student must measure the time for one clap–echo cycle (the time period between successive claps).
4. Speed is calculated by dividing the total distance (2 × distance to wall) by the time for one cycle, using speed = distance ÷ time.

## Key terms

- [echo](https://www.gradenine.co.uk/glossary/echo)
- [speed of sound](https://www.gradenine.co.uk/glossary/speed-of-sound)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-measures-the-speed-of-32beb3d1) · Published by Druglandscape Ltd.