# Explain what happens to a water wave when it passes through a gap in a barrier that is approximately the same width as its wavelength, and describe how the pattern of the wave changes if the frequency of the wave is then increased while the gap stays the same size.

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

## Mark scheme (5 marks)

1. The water wave spreads out / bends around the edges of the gap after passing through it
2. This effect is called diffraction
3. Maximum diffraction / greatest spreading occurs when the gap width is approximately equal to the wavelength
4. Increasing the frequency decreases the wavelength (at constant wave speed)
5. With a shorter wavelength the gap is now much wider than the wavelength, so the wave diffracts less / spreads out less

## Key terms

- [wavelength](https://www.gradenine.co.uk/glossary/wavelength)
- [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-what-happens-to-a-water-a4428932) · Published by Druglandscape Ltd.