# A thermistor and a fixed resistor are connected in series with a battery. Explain what happens to the total resistance of the circuit and the current flowing through it when the temperature of the thermistor increases.

> OCR A-Level Physics A (H556) — 3.4 Materials · Explain · 5 marks

> A thermistor is used in a temperature-monitoring circuit. As the room warms up, the temperature of the thermistor rises.

## Mark scheme (5 marks)

1. The resistance of the thermistor decreases as temperature increases
2. The total resistance of the series circuit decreases
3. In a series circuit the total resistance equals the sum of the individual resistances (so a fall in one reduces the total)
4. Current is directly proportional to potential difference / voltage is constant so lower resistance means greater current (correct use of V = IR reasoning)
5. Current is the same at every point in the series circuit (so the increased current is the same through both the thermistor and the fixed resistor)

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-and-a-fixed-resistor-124c9b9b) · Published by Druglandscape Ltd.