# A street lighting system uses light dependent resistors (LDRs) to automatically switch lights on at night and off during the day. Explain how the resistance of an LDR changes between daytime and night-time, and describe how this change in resistance affects the current in the circuit.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.1 Motion · Explain · 5 marks

> Street lighting engineers design circuits that respond automatically to changing light levels throughout the day and night, without any manual switching.

## Mark scheme (5 marks)

1. The resistance of the LDR is low during the day / when light intensity is high
2. The resistance of the LDR is high at night / when light intensity is low
3. Current and resistance are inversely related / as resistance increases, current decreases (and vice versa)
4. At night, the LDR's high resistance causes a low current to flow in the circuit
5. During the day, the LDR's low resistance allows a larger current to flow in the circuit

## Key terms

- [resistance](https://www.gradenine.co.uk/glossary/resistance)
- [current](https://www.gradenine.co.uk/glossary/current)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-street-lighting-system-uses-light-e30ab79f) · Published by Druglandscape Ltd.