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GCSE Physics · key term
A light-dependent resistor: a component whose resistance decreases as the intensity of light falling on it increases.
Used by AQA and OCR
Specification 4.2.1.1, 4.2.1.4 · Paper 1
A light-dependent resistor whose resistance decreases as the light falling on it becomes brighter.
Revise: Standard circuit diagram symbolsStandard circuit symbols: Cell; Battery; Open switch; Lamp; Fuse; Ammeter; Voltmeter; Resistor; Variable resistor; Thermistor; LDR; Diode; LED. Resistors and related components use the European rectangular style.
Do not say that a thermistor or LDR switches an appliance directly. Its changing resistance provides an electrical change that a control circuit can use to operate a switch.
Keep the relationships distinct: a hotter thermistor has lower resistance; a hotter filament lamp has higher resistance; an LDR in brighter light has lower resistance.
When comparing readings, state what you changed and what you kept constant. Heating a wire or changing the light falling on an LDR can alter its resistance.
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Specification P3.2f, P3.2h · Paper 1 (Foundation), Paper 3 (Higher)
A light-dependent resistor whose resistance decreases as the light falling on it becomes more intense.
Revise: Circuit design for resistance effectsFor an LDR, change the light falling on it, for example by moving a lamp to different distances while keeping the lamp and surrounding lighting otherwise the same. Take a fresh pair of electrical readings each time. Its resistance falls as the light becomes more intense.
A light-dependent resistor whose resistance falls as the light intensity falling on it rises.
Paper 1, Paper 2
A light-dependent resistor: a component whose resistance decreases as light intensity increases.
Revise: Investigating I-V Characteristics of ComponentsAn LDR and a thermistor have resistances that depend on an environmental condition as well as on their electrical operating point.