Investigating Resistance in Thermistors & LDRs (AQA GCSE Combined Science: Trilogy: Physics): Revision Note

Investigating Resistance in Thermistors & LDRs

• To investigate the relationship between the resistance of a thermistor and temperature, or the resistance of an LDR and light intensity, the following circuits must be set up:

• For the LDR circuit:

  • Begin with the lamp turned off in a dark room

  • Record the reading on the voltmeter and ammeter

  • Slowly increase the light intensity of the lamp using the dimmer switch

  • Record the reading on the voltmeter and ammeter for each increase in light intensity

• For the thermistor circuit:

  • Begin with the heater turned off

  • Record the reading on the voltmeter and ammeter

  • Slowly increase the heat of the heater using the dimmer switch

  • Record the reading on the voltmeter and ammeter for each increase in temperature of the heater

• In both situations, make sure the lamp and heater are close, but not touching, the LDR and thermistor respectively

• Wait a few seconds before taking the voltmeter and ammeter readings to allow the LDR and thermistor to react to the change in the environment

• Calculate the resistance of the LDR or thermistor for each change in light intensity or temperature using the equation:

• Therefore, to measure the resistance of any component in a circuit, make sure the following are included in the circuit diagrams:

  • The ammeter is connected in series to the component

  • The voltmeter is connected in parallel to the component

  • The component with the appropriate circuit symbol

  • The component is connected to a power supply with a low voltage (below 15 V) otherwise too high a current in the circuit will start to affect the resistance of the component

Circuit diagram for investigating the resistance of a component