# A sound wave travelling through air reaches a boundary and enters water. Describe what happens to the speed, wavelength and frequency of the sound wave as it crosses this boundary, and explain why the wavelength changes.

> Edexcel GCSE Physics (1PH0) — 4.1 Waves · Describe · 4 marks

> Sound waves travel through different media. The speed of sound in water is greater than the speed of sound in air.

## Mark scheme (4 marks)

1. The speed of the sound wave increases as it enters water.
2. The frequency of the sound wave remains constant / does not change.
3. The wavelength of the sound wave increases.
4. Because speed increases but frequency is constant, wavelength must increase (linking wave equation v = fλ or equivalent reasoning).

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Physics (1PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-sound-wave-travelling-through-air-0125c726) · Published by Druglandscape Ltd.