# A student investigates the emission of electrons from a zinc plate using ultraviolet light. The student finds that when dim ultraviolet light is used, electrons are emitted instantly, but when bright red light is used, no electrons are emitted at all. Explain these observations using the photon model of light.

> Eduqas A-Level Physics — 3.2 Photon and particle properties · Explain · 5 marks

## Mark scheme (5 marks)

1. A photon is a discrete packet (quantum) of energy
2. A single photon interacts with a single electron (one-to-one interaction)
3. Ultraviolet photons have sufficient energy to exceed the work function / release electrons immediately regardless of intensity
4. Red light photons have lower frequency than ultraviolet photons, so each red photon has less energy
5. Red photons have insufficient energy to overcome the work function, so no electrons are emitted no matter how bright the light is

## Key terms

- [photon](https://www.gradenine.co.uk/glossary/photon)
- [emission](https://www.gradenine.co.uk/glossary/emission)

## Related

- [Revision notes for Eduqas A-Level Physics](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-student-investigates-the-emission-of-aa5c6812) · Published by Druglandscape Ltd.