# A student stands between two parallel walls that are far apart and shouts once. The student hears two separate echoes, one from each wall. Explain why the student hears two separate echoes rather than one, and state what property of sound makes echoes possible.

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

## Mark scheme (4 marks)

1. Sound is reflected (at each wall / off the surfaces)
2. The two walls are at different distances from the student
3. Sound travels at a finite / fixed speed, so it takes a different (longer / shorter) time to reach each wall and return
4. The two echoes therefore arrive back at the student at different times

## Key terms

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

## 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-stands-between-two-parallel-c01e2ac0) · Published by Druglandscape Ltd.