# Explain why increasing the intensity of light does not cause photoelectric emission from a metal surface, but increasing the frequency of light above the threshold frequency does.

> WJEC A-Level Physics (Wales) — 3.2 Photon and particle properties · Explain · 5 marks

> When light shines on a metal surface, electrons may be emitted. This is called the photoelectric effect. Scientists found that whether electrons are emitted depends on the frequency of the light, not its intensity.

## Mark scheme (5 marks)

1. Light consists of photons (packets/quanta of energy)
2. Each photon interacts with one electron only (one-to-one interaction)
3. Increasing intensity increases the number of photons but not the energy of each photon
4. Each photon must have enough energy to overcome the work function (minimum energy needed to release an electron)
5. Higher frequency means higher energy photon (energy depends on frequency), so above the threshold frequency each photon has enough energy to release an electron

## Key terms

- [threshold frequency](https://www.gradenine.co.uk/glossary/threshold-frequency)
- [intensity](https://www.gradenine.co.uk/glossary/intensity)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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/explain-why-increasing-the-intensity-of-80cbc3ac) · Published by Druglandscape Ltd.