# A student sets up a series circuit containing a battery, a switch, and two resistors. She notices that when she adds a third resistor in series, all the components become dimmer. Explain why adding a third resistor in series causes the current in the circuit to decrease, and describe what happens to the voltage across the battery as the third resistor is added.

> Eduqas GCSE Physics — 7.2 Series and parallel circuits · Explain · 4 marks

## Mark scheme (4 marks)

1. Adding a third resistor increases the total resistance of the circuit
2. Because the voltage of the battery stays the same / is fixed, a higher resistance means a smaller current (reference to V = IR or equivalent reasoning)
3. In a series circuit the same current flows through every component, so all components receive less current / become dimmer
4. The voltage across the battery remains the same / does not change when the third resistor is added

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Physics](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-sets-up-a-series-2ddb8f05) · Published by Druglandscape Ltd.