# A student claps their hands once whilst standing a large distance from a tall cliff face. They hear two sounds: the original clap and then an echo a short time later. Explain how the echo is produced and state what measurements the student would need to take in order to determine the speed of sound in air.

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

> Sound waves are longitudinal waves that can be reflected. When a sound wave strikes a solid boundary, it bounces back towards the source. A student uses this property to measure the speed of sound.

## Mark scheme (4 marks)

1. The sound wave from the clap travels to the cliff face and is reflected back towards the student.
2. The reflected wave reaching the student's ears is heard as the echo.
3. The student must measure the distance between themselves and the cliff face.
4. The student must measure the time between the original clap and the echo being heard, and use speed = distance / time where the total distance is twice the distance to the cliff.

## Key terms

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

## 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-claps-their-hands-once-e5417ca0) · Published by Druglandscape Ltd.