O-LevelPhysicsElectricity5054/11 · May/June 2024 · Q321 Mark
A light-dependent resistor (LDR) is to be used as an input sensor for an intruder alarm circuit. When there is no light on the LDR, the lamp switches on. The resistance of the fixed resistor is less than that of the lamp. Which diagram shows the circuit?
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ACircuit diagram A with LDR in series with lamp, and fixed resistor in parallel with LDR
BCircuit diagram B with LDR in series with fixed resistor, and lamp in parallel with fixed resistor
CCircuit diagram C with LDR in series with fixed resistor, and lamp in parallel with LDR
DCircuit diagram D with LDR in series with lamp, and fixed resistor in parallel with lamp
✓ Correct answer
B: Circuit diagram B with LDR in series with fixed resistor, and lamp in parallel with fixed resistor
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