# Explain why a dim source of light with a high enough frequency can release electrons from a metal surface, but a very bright source of light with a lower frequency cannot.

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

> In the photoelectric effect, the emission of electrons from a metal surface depends on the properties of the light used.

## Mark scheme (5 marks)

1. Light is made up of photons (discrete packets/quanta of energy)
2. The energy of a photon depends on its frequency (not intensity)
3. A single photon must have enough energy to overcome the work function of the metal in order to release an electron
4. The high-frequency (dim) source has photons with enough energy to exceed the work function, so electrons are released
5. The low-frequency (bright) source has photons with insufficient energy to overcome the work function, so no electrons are released regardless of intensity

## Key terms

- [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-a-dim-source-of-7c00eaf6) · Published by Druglandscape Ltd.