# Describe what happens to a water wave as it passes through a narrow gap in a barrier, and explain how the width of the gap affects the extent of this effect.

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

> Water waves in a ripple tank travel towards a barrier that has a narrow gap cut into it.

## Mark scheme (5 marks)

1. The wave spreads out (beyond the gap) / bends around the edges of the gap
2. This effect is called diffraction
3. The effect is greatest when the gap width is similar to (or equal to) the wavelength of the wave
4. When the gap is much wider than the wavelength, the wave passes through with very little spreading / diffraction is reduced
5. When the gap is much narrower than the wavelength, the wave is mostly reflected / very little energy passes through / the transmitted wave is very weak

## Key terms

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

## Related

- [Revision notes for AQA A-Level Physics (7408)](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/describe-what-happens-to-a-water-d47b5f56) · Published by Druglandscape Ltd.