# A chef places a tray of food into an industrial oven that uses infrared radiation to cook the food. The tray is made from a shiny metal surface. Explain why the shiny metal tray reflects most of the infrared radiation incident on it, and describe what would happen to the frequency and wavelength of the infrared waves as they pass from the air into the denser glass viewing window of the oven door.

> OCR A-Level Physics A (H556) — 5.1 Thermal physics · Explain · 5 marks

> Infrared radiation is used in industrial ovens to heat food. The oven door contains a thick glass viewing window. The metal tray inside the oven has a smooth, shiny surface.

## Mark scheme (5 marks)

1. The shiny/smooth metal surface causes specular reflection
2. The angle of incidence equals the angle of reflection (law of reflection)
3. The frequency of the infrared waves remains constant / does not change as the waves enter the glass
4. The speed of the infrared waves decreases as they enter the denser glass medium
5. Because frequency is constant and speed decreases, the wavelength also decreases

## Key terms

- [infrared radiation](https://www.gradenine.co.uk/glossary/infrared-radiation)
- [frequency](https://www.gradenine.co.uk/glossary/frequency)
- [wavelength](https://www.gradenine.co.uk/glossary/wavelength)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-chef-places-a-tray-of-b362d307) · Published by Druglandscape Ltd.