# Sound is described as a longitudinal wave. Explain what this means and describe how sound travels through air, referring to compressions and rarefactions.

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

## Mark scheme (4 marks)

1. In a longitudinal wave, the oscillations/vibrations are parallel to (in the same direction as) the direction of travel/energy transfer.
2. Sound causes air particles to be pushed together, forming compressions (regions of higher pressure/density).
3. Between compressions, particles are spread further apart, forming rarefactions (regions of lower pressure/density).
4. Energy is transferred through the air as these compressions and rarefactions pass through the medium, but the air particles themselves are not carried along/do not travel with the wave.

## Key terms

- [longitudinal wave](https://www.gradenine.co.uk/glossary/longitudinal-wave)
- [compression](https://www.gradenine.co.uk/glossary/compression)
- [rarefaction](https://www.gradenine.co.uk/glossary/rarefaction)

## 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/sound-is-described-as-a-longitudinal-e9fae93e) · Published by Druglandscape Ltd.