# Explain why a sound wave and a light wave behave differently when they each pass through a gap of the same width, and explain how changing the frequency of the sound wave affects the amount of diffraction that occurs.

> AQA A-Level Physics (7408) — 3.3.2 Refraction, Diffraction and Interference · Explain · 5 marks

> A sound wave of frequency 500 Hz and a beam of visible light both pass through a gap of the same width in a barrier.

## Mark scheme (5 marks)

1. Diffraction occurs when a wave passes through a gap (or around an obstacle)
2. Diffraction is greatest when the gap width is approximately equal to (or smaller than) the wavelength of the wave
3. Sound has a much longer wavelength than visible light (so the gap is closer to the wavelength of sound)
4. Therefore sound diffracts (spreads out) much more than light through the same gap
5. Decreasing the frequency of the sound wave increases its wavelength, making the gap comparatively smaller relative to wavelength — so diffraction increases; increasing frequency decreases wavelength, reducing diffraction

## Key terms

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

## Related

- [Revision notes for AQA A-Level Physics (7408)](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/explain-why-a-sound-wave-and-adb66087) · Published by Druglandscape Ltd.