# A student is investigating the emission of light from a LED (light-emitting diode). The student knows that electrons inside the LED lose energy and that this energy is released as photons. The LED emits green light of frequency 5.5 × 10¹⁴ Hz. The student is told that a second LED emits photons of lower frequency than the green LED. Explain what this tells us about the energy of each photon emitted by the second LED, and describe how the energy of a photon is related to its frequency.

> WJEC A-Level Physics (Wales) — 2.7 Photons · Explain · 5 marks

> A LED converts electrical energy into light by releasing photons when electrons lose energy inside the device.

## Mark scheme (5 marks)

1. A photon is a packet (quantum) of electromagnetic energy
2. The energy of a photon is directly proportional to its frequency (E ∝ f / E = hf)
3. h is the Planck constant (a fixed/constant value)
4. The second LED emits photons of lower energy than the green LED
5. Each electron in the second LED loses less energy when it releases a photon (compared to the green LED)

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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-is-investigating-the-emission-335552c4) · Published by Druglandscape Ltd.