# A beam of white light passes through a red colour filter and then strikes a rough white surface. Explain what the observer sees after the light has interacted with both the filter and the rough surface, and explain why each effect occurs.

> Edexcel A-Level Physics (9PH0) — 5.1 Wave properties · Explain · 5 marks

> White light is made up of all the colours of the visible spectrum. Colour filters and surface texture both affect how light behaves.

## Mark scheme (5 marks)

1. The colour filter absorbs all colours except red (or: only red wavelengths are transmitted through the filter).
2. So only red light reaches the rough surface (correct consequence of filtering).
3. The rough surface causes diffuse reflection (naming the process).
4. Diffuse reflection scatters the red light in many different directions (because the surface has many different angles / orientations of tiny surfaces).
5. The observer sees red light coming from the surface (scattered / spread in many directions so visible from different positions).

## Key terms

- [colour filter](https://www.gradenine.co.uk/glossary/colour-filter)
- [white light](https://www.gradenine.co.uk/glossary/white-light)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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/a-beam-of-white-light-passes-163f09e7) · Published by Druglandscape Ltd.