Thermistors (AQA GCSE Physics): Revision Note
Exam code: 8463
Thermistors
A thermistor is a non-ohmic conductor and a temperature-dependent resistor
It is represented by the following circuit symbol:
Thermistor circuit symbol
The resistance of a thermistor changes depending on its temperature
As the temperature increases the resistance of a thermistor decreases and vice versa
The resistance through a thermistor is dependent on the temperature of it
Applications of Thermistors
A thermistor is a temperature sensor and is regularly used in a thermostat
This means the circuit automatically regulates temperature or switches a device on or off when the temperature reaches a certain value
Therefore, thermistors are found in:
Ovens
Refrigerators
Fire alarms
Digital thermometers
Boilers
They are commonly used to regulate and monitor the temperature in environments where it must be carefully controlled eg. food and beverage factories
A digital thermometer uses a thermistor to display a temperature reading
Examiner Tips and Tricks
If a question asks you to choose a thermistor to measure a temperature, look at the temperature range given in the question. The best choice is the thermistor whose resistance changes the most over that range, which is where its graph is steepest. A common mistake is to pick the thermistor with the lowest resistance, so make sure you say that its resistance changes the most over that range.
Remember to draw the thermistor symbol exactly as it is shown earlier in these notes, because it is easy to lose a mark by drawing it slightly differently.
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