# A student claps two wooden blocks together once near a large flat wall and hears an echo a short time later. Explain why the echo is heard and describe what happens to the frequency, wavelength, and speed of the sound when it reflects off the wall.

> Cambridge International IGCSE Physics (0625) — 3.4 Sound · Explain · 4 marks

## Mark scheme (4 marks)

1. The sound reflects off the wall (bounces back from the surface / boundary).
2. The reflected sound travels back to the student, so it is heard after the original sound (as an echo).
3. The frequency of the sound is unchanged after reflection.
4. Both the wavelength and the speed of the sound are also unchanged after reflection.

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](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-two-wooden-blocks-abbb80e1) · Published by Druglandscape Ltd.