# Explain why increasing the frequency of light shone onto a metal surface increases the maximum kinetic energy of the electrons emitted, but increasing the intensity of the same frequency light does not.

> AQA A-Level Physics (7408) — 3.2.2 EM Radiation and Quantum Phenomena · Explain · 5 marks

> A metal surface emits electrons when light above a certain frequency is shone onto it. This is known as the photoelectric effect.

## Mark scheme (5 marks)

1. Light consists of photons (packets/quanta of energy)
2. The energy of a photon depends on (is proportional to) its frequency
3. A single photon interacts with a single electron; greater photon energy means more energy transferred to the electron
4. After the work function energy is used to free the electron, any remaining energy becomes kinetic energy of the electron, so higher frequency means greater maximum kinetic energy
5. Increasing intensity means more photons per second but each photon still has the same energy, so each electron still receives the same energy and maximum kinetic energy is unchanged

## Key terms

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

## Related

- [Revision notes for AQA A-Level Physics (7408)](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-frequency-of-ea5de773) · Published by Druglandscape Ltd.