# A student connects a filament lamp and a thermistor in series with a battery. As the circuit is left switched on, the filament lamp glows brightly and the thermistor warms up. Explain what happens to the current in the circuit as the thermistor warms up, and why this affects the brightness of the filament lamp.

> Edexcel A-Level Physics (9PH0) — 10.1 Stars, life cycles and cosmology · Explain · 5 marks

> A student connects a filament lamp and a thermistor in series with a battery. As the circuit is left switched on, the filament lamp glows brightly and the thermistor warms up.

## Mark scheme (5 marks)

1. As the thermistor warms up, its resistance decreases
2. Because the components are in series, the total resistance of the circuit decreases
3. A smaller total resistance means a larger current flows through the circuit
4. In a series circuit the same current passes through all components, so the current through the filament lamp increases
5. A greater current through the filament lamp means more power is transferred, so the lamp glows more brightly

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-connects-a-filament-lamp-024f8585) · Published by Druglandscape Ltd.