# A student shines ultraviolet light onto a zinc plate. The ultraviolet light causes electrons to be released from the zinc plate. The student then replaces the ultraviolet light with visible red light of the same intensity. No electrons are released. Explain why ultraviolet light releases electrons from the zinc plate but red light of the same intensity does not.

> Eduqas A-Level Physics — 2.7 Photons · Explain · 5 marks

## Mark scheme (5 marks)

1. Light travels as discrete packets of energy called photons
2. The energy of a photon depends on its frequency
3. Ultraviolet light has a higher frequency than red light, so each ultraviolet photon carries more energy than each red photon
4. A minimum amount of energy is needed to release an electron from the zinc plate
5. Each red photon does not have enough energy to release an electron, and photons cannot combine their energies, so no electrons are released

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-shines-ultraviolet-light-onto-34074e08) · Published by Druglandscape Ltd.