# A harbour wall has a narrow opening that allows ocean waves to enter a sheltered bay. A boat captain observes that the waves spread out in a curved pattern after passing through the opening. Explain why the waves spread out after passing through the narrow opening, and describe how the amount of spreading would change if the opening were made much wider.

> OCR GCSE Physics A: Gateway Science (J249) — P4.1 Wave behaviour · Explain · 4 marks

> Ocean waves approach a harbour wall. The harbour wall has a narrow opening. After passing through the opening, the waves spread out into the sheltered bay beyond.

## Mark scheme (4 marks)

1. The spreading of waves through a gap is called diffraction
2. Diffraction occurs because the gap causes the waves to bend / spread around the edges of the opening
3. The amount of diffraction / spreading is greatest when the gap width is similar to (or smaller than) the wavelength of the waves
4. If the opening is made much wider, there is less / less noticeable diffraction, so the waves spread out less / the waves pass through more like straight wavefronts

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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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