Energy and Voltage in Circuits
3 marks · NormalExplain, with reasons, why LDRs are often used in automatic lighting systems. State how their resistance changes with light intensity.
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Common mistakes: Getting resistance change wrong; Not linking to automatic systems
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Marking points
M1 · 1 mark · States that LDR resistance decreases as light intensity increases.
B1 · 1 mark · Explains that this property allows automatic lights to switch on when it gets dark.
B2 · 1 mark · Describes a practical use such as streetlights or security lights.
Worked solution
An LDR’s resistance decreases as light intensity increases. In automatic lighting, when it gets dark, the resistance is high, so the circuit can be designed to turn a lamp on. This makes LDRs useful for automatic outdoor or security lights that need to operate when it is dark.