3.5 - Investigating Components

Investigating LDRs and thermistors

• The resistance of a light-dependent resistor (LDR) and a thermistor depends on outside conditions: light level for an LDR and temperature for a thermistor.
• The standard test circuit can be adapted to investigate this: hold the supply potential difference constant and change the outside condition instead.

How to investigate each

• Thermistor - Keep the supply potential difference constant and gradually heat the thermistor (e.g. in a beaker of hot water). As the temperature rises, the current increases because its resistance falls.
• LDR - In a dim room, keep the supply potential difference constant and vary the light level near the LDR (e.g. using a lamp on a dimmer switch). As the light gets brighter, the current increases because its resistance falls.