# Describe the properties of laser light that make it different from the light produced by a torch, and explain why these properties make lasers suitable for reading data from a compact disc (CD).

> WJEC A-Level Physics (Wales) — 2.8 Lasers · Describe and Explain · 5 marks

> Lasers are used in many everyday devices, including CD players, barcode scanners and medical equipment. The light they produce has special properties that make them useful for such precise tasks.

## Mark scheme (5 marks)

1. Laser light is monochromatic (single colour / single wavelength / single frequency)
2. Laser light is coherent (waves are in phase / all waves have the same phase relationship)
3. Laser light is collimated / forms a narrow parallel beam that does not spread out
4. The narrow / focused beam can be directed precisely onto the small pits and lands on the surface of the CD
5. The reflected light is detected and the pattern of reflections is used to decode / read the data stored on the CD

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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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