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GCSE Physics · key term
A light-sensitive resistor whose resistance decreases as the intensity of the light falling on it increases.
Used by Edexcel and OCR
Specification 10.19, 10.21 · Paper 2
A resistor whose resistance changes according to the intensity of light falling on it.
Revise: LDR ResistanceA light-dependent resistor, or LDR, is a circuit component that responds to its surroundings.
Specification P3.2b · Paper 1 (Foundation), Paper 3 (Higher)
A light-dependent resistor whose resistance normally decreases as the light intensity increases.
Revise: Circuit diagramsAn LDR is based on a resistor symbol with arrows pointing towards it. The arrows represent incoming light. Its resistance decreases as the light intensity increases, allowing a circuit to respond to changing light levels.
Paper 1, Paper 2
A component whose resistance decreases as the intensity of light falling on it increases.
Revise: Sensing Circuits: LDRs and ThermistorsLDRs and thermistors can also be placed in the test circuit while current and potential difference are varied. Their measured behaviour depends strongly on their surroundings, so light intensity must be controlled for an LDR and temperature must be controlled for a thermistor. A thermistor should be tested with small currents where possible because the current itself can heat it and alter the condition being measured.
State both directions of the relationship: increasing light intensity decreases an LDR’s resistance; decreasing light intensity increases it.
For thermistors and LDRs, distinguish the variable you change from the electrical quantity you measure: change temperature or light intensity, then determine resistance.
Do not confuse the arrows on sensor symbols: arrows towards an LDR represent incoming light.
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