# A thermistor is used in a temperature-monitoring circuit. As the temperature of the thermistor increases, the current measured by the ammeter in the circuit also increases. Explain why the current increases as the temperature of the thermistor rises.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.2 Forces in action · Explain · 5 marks

> A thermistor is connected in series with an ammeter and a battery supplying a constant potential difference. When the thermistor is placed in warm water, the reading on the ammeter increases compared to when it is placed in cold water.

## Mark scheme (5 marks)

1. As temperature increases, the resistance of the thermistor decreases
2. The potential difference across the circuit remains constant (supplied by the battery)
3. Using the relationship voltage = current × resistance (or current = voltage / resistance)
4. Because resistance is lower, electrons can flow more easily / there is less opposition to the flow of charge
5. Therefore the rate of flow of charge increases, so the current is greater

## Key terms

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

## 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-thermistor-is-used-in-a-8022ff81) · Published by Druglandscape Ltd.