# A surgeon uses an endoscope to view inside a patient's body. The endoscope contains optical fibres made of glass. Explain how total internal reflection allows light to travel along a bent optical fibre and reach the surgeon's eye.

> Pearson Edexcel International GCSE Physics (4PH1) — 3.3 Light and sound · Explain · 4 marks

> An endoscope is a flexible medical instrument that uses bundles of optical fibres to carry light into and out of the body. Each optical fibre is a thin rod of glass surrounded by a less optically dense cladding material.

## Mark scheme (4 marks)

1. Light travels from a more optically dense medium (glass) into a less optically dense medium (cladding/air)
2. The angle of incidence at the glass–cladding boundary must be greater than the critical angle
3. All the light is reflected back into the glass / no light escapes through the boundary
4. This reflection repeats along the length of the fibre, allowing light to travel the full length even when the fibre is bent

## Key terms

- [total internal reflection](https://www.gradenine.co.uk/glossary/total-internal-reflection)
- [optical fibre](https://www.gradenine.co.uk/glossary/optical-fibre)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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-surgeon-uses-an-endoscope-to-75225d3a) · Published by Druglandscape Ltd.