# Explain why a light dependent resistor (LDR) is useful in an automatic street-lighting circuit that switches the lights on when it gets dark.

> AQA GCSE Physics (8463) — 4.2.1 Current, potential difference and resistance · Explain · 4 marks

> An automatic street light uses an LDR in its circuit. The street light switches on when the surrounding light intensity falls below a certain level.

## Mark scheme (4 marks)

1. As light intensity decreases / it gets dark, the resistance of the LDR increases
2. Greater resistance means a smaller current flows (for the same potential difference)
3. The change in current (or resistance) can be detected / used to trigger / switch on the street light
4. The LDR responds automatically to the level of light / no manual switching is needed

## Key terms

- [light dependent resistor (LDR)](https://www.gradenine.co.uk/glossary/light-dependent-resistor-ldr)

## Related

- [Revision notes for AQA GCSE Physics (8463)](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-light-dependent-resistor-d4aafe0d) · Published by Druglandscape Ltd.