# A student investigates how the resistance of a thermistor changes with temperature. The student places the thermistor in water and gradually increases the water temperature from 10 °C to 60 °C, measuring the current at each temperature whilst keeping the potential difference constant. Explain what happens to the current through the thermistor as the temperature of the water increases, and why this behaviour makes thermistors useful in temperature-sensing devices.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.4 Materials · Explain · 5 marks

> A thermistor is a temperature-dependent component used in many electronic sensing circuits. Unlike ordinary resistors, its resistance changes significantly with temperature.

## Mark scheme (5 marks)

1. As temperature increases, the resistance of the thermistor decreases
2. Because resistance decreases, the current through the thermistor increases (at constant potential difference)
3. The changing resistance (or current) gives a measurable, predictable output that corresponds to a specific temperature
4. This allows the thermistor to be used in a circuit where the current or voltage across it acts as an indicator of temperature (e.g. in a thermostat or temperature alarm)
5. Contrast with an ordinary (ohmic) conductor: for an ohmic conductor at constant temperature, current is directly proportional to potential difference and resistance does not change in this way, whereas a thermistor's resistance changes significantly with temperature

## Key terms

- [thermistor](https://www.gradenine.co.uk/glossary/thermistor)
- [resistance](https://www.gradenine.co.uk/glossary/resistance)
- [current](https://www.gradenine.co.uk/glossary/current)
- [potential difference](https://www.gradenine.co.uk/glossary/potential-difference)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-investigates-how-the-resistance-79eb866c) · Published by Druglandscape Ltd.