# The photoelectric effect cannot be explained using a wave model of light. Explain how the photon model of light accounts for the key observations of the photoelectric effect.

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

> When ultraviolet light is shone onto a clean zinc plate, electrons are emitted from the surface immediately, even at very low light intensities. If red light is used instead, no electrons are emitted regardless of the intensity.

## Mark scheme (5 marks)

1. Light (electromagnetic radiation) is made up of discrete packets of energy called photons
2. Each photon interacts with only one electron (one-to-one interaction), so the electron receives all of one photon's energy in a single interaction
3. The energy of a photon depends on its frequency (E = hf), so ultraviolet photons have higher energy than red photons
4. There is a minimum energy (the work function) needed to release an electron from the metal surface; if the photon energy is below this, no emission occurs regardless of intensity
5. Emission is immediate because a single photon of sufficient energy can release an electron instantly, with no need for energy to build up over time

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/the-photoelectric-effect-cannot-be-explained-d06f5e24) · Published by Druglandscape Ltd.