Thermistor

Key Stage 4

The symbol for a thermistor.

A thermistor is a resistor which changes resistance depending on the temperature.

'NTC' thermistors decrease resistance as the temperature increases. (NTC = Negative Temperature Coefficient.)

A thermistor can be used to control the current passing through a circuit. If the potential difference is constant then the current decreases as temperature decreases.

A thermistor can be used to control the potential difference of another component in series with it. If the temperature is decreased then the potential difference across other components will decrease.

Thermistors can be used temperature sensors.

The IV Graph for an 'NTC' thermistor shows that:

At a high temperature the current increases rapidly with the potential difference
At a low temperature the current increases slowly with the potential difference.

The resistance of an 'NTC' thermistor increases as the temperature decreases.

	Connect an ammeter in series with the thermistor to measure current through the thermistor. Connect a voltmeter in parallel with the thermistor to measure the potential difference across it. Use a variable resistor in series with the thermistor to vary the potential difference across the thermistor. Place the thermistor in a beaker of cold water around 5°C. Start with a potential difference of zero and increase the potential difference by an interval of 0.2V up to 2V. Recording the reading on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current. Repeat steps 5-7 with the thermistor in a beaker of hot water around 40°C.