Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Describe how the resistance of a thermistor varies with change of…
Full specification wording
Topic 10 – Electricity and circuits: 10.20 Describe how the resistance of a thermistor varies with change of temperature (negative temperature coefficient thermistors only)
A negative temperature coefficient (NTC) thermistor is a resistor whose resistance falls as its temperature rises.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 19 of 39
Study notes
From the checked teaching notes for this specification point.
The idea
A negative temperature coefficient (NTC) thermistor is a resistor whose resistance falls as its temperature rises. At low temperature the resistance is high, so a small current flows for a given voltage. As the thermistor warms, more charge carriers become available in the semiconductor, so the resistance decreases and the current increases. The change is not proportional: the resistance falls steeply over a certain temperature range and changes less at other temperatures. The term negative temperature coefficient means the resistance changes in the opposite direction to temperature. This behaviour makes an NTC thermistor useful as a temperature sensor, for example in a circuit that responds when something becomes too hot. When answering, state the direction of the change and make clear that only NTC thermistors are being described.
What earns the marks
- States that resistance is high when temperature is low.
- States that resistance falls as temperature rises for an NTC thermistor.
- Explains that the negative temperature coefficient means resistance changes in the opposite direction to temperature.
- Links the fall in resistance to more charge carriers becoming available as temperature rises.
- Applies the thermistor to a temperature-sensing circuit.
Common mistakes and how to put them right
Claims that resistance rises with temperature.
Put it right by stating that an NTC thermistor has lower resistance when hotter.
Describes a positive temperature coefficient behaviour.
Put it right by keeping to NTC thermistors only.
Treats the change as directly proportional.
Put it right by noting the resistance falls steeply over part of the range and less elsewhere.
Exam tips
- State clearly that the thermistor is an NTC type before describing the change.
- Give the direction of change in one sentence: as temperature rises, resistance falls.
- Link the change to charge carriers to gain the explanation mark.
Try the lesson
The start of the Topic 10 – Electricity and circuits: 10.20 Describe how the resistance of a thermistor varies with change of temperature (negative temperature coefficient thermistors only) lesson, made from checked teaching notes for this specification point.
Have a go first
A student warms a negative temperature coefficient (NTC) thermistor. What happens to the resistance of the thermistor as its temperature rises?
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