1. IP2.23.4 Thermistors © Oxford University Press 2011 Thermistors

2. IP2.23.4 Thermistors © Oxford University Press 2011  A thermistor is another special type of resistor. Its resistance changes as its temperature changes.  When the temperature of the thermistor is low, its resistance is high. This is because a thermistor is made of a material which does not conduct electricity well at low temperatures. The outer electrons are loosely bound to the atoms and are not free to flow through the thermistor.  As the temperature increases, more outer electrons gain enough energy to break free from atoms. The electrons are then free to flow through the thermistor.

3. IP2.23.4 Thermistors © Oxford University Press 2011  This graph shows the thermistor’s resistance against temperature.  Remember, the resistance of a thermistor decreases as the temperature increases.

4. IP2.23.4 Thermistors © Oxford University Press 2011  This change in resistance according to their temperature means that thermistors can be used as temperature sensors.  For example, they can be used to warn drivers when the car engine is overheating.

5. IP2.23.4 Thermistors © Oxford University Press 2011 Most thermistors have a useful working range of –90 °C to 200 °C.