# A student shines monochromatic light onto a metal surface and observes that electrons are emitted. The student then replaces the light source with one that emits light of the same intensity but a lower frequency. No electrons are emitted. Explain these observations in terms of photons and the work function of the metal.

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

## Mark scheme (5 marks)

1. Light is made up of photons / light energy is quantised into photons
2. Each photon has an energy that depends on its frequency (E = hf, so higher frequency means higher photon energy)
3. The work function is the minimum energy needed to release an electron from the metal surface
4. With the first source, photon energy is greater than or equal to the work function, so electrons are released
5. With the lower frequency source, each photon has insufficient energy to overcome the work function, so no electrons are emitted regardless of intensity

## Key terms

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

## 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/a-student-shines-monochromatic-light-onto-dce1b8da) · Published by Druglandscape Ltd.