# A torch contains three identical cells connected in series, each with an electromotive force (EMF) of 1.5 V. The torch has two identical bulbs connected in parallel with each other, and this parallel combination is connected in series with a switch and the cells. Explain what happens to the brightness of the remaining bulb and the current drawn from the cells when one bulb breaks and stops working.

> WJEC A-Level Physics (Wales) — 2.2 DC circuits · Explain · 5 marks

> A torch contains three identical cells connected in series. The torch circuit has two identical bulbs connected in parallel with each other, and this parallel combination is connected in series with a switch and the cells.

## Mark scheme (5 marks)

1. The total EMF of the cells is 4.5 V (three cells × 1.5 V each), and this voltage is applied across both bulbs / the parallel combination
2. In a parallel circuit, each branch has the same potential difference across it, so the remaining working bulb still has the full 4.5 V across it
3. Because the voltage across the remaining bulb is unchanged, it glows at the same brightness as before
4. When one bulb breaks, there is one fewer parallel branch, so the total resistance of the circuit increases
5. Because the total resistance increases and the EMF is unchanged, the total current drawn from the cells decreases

## Key terms

- [electromotive force (EMF)](https://www.gradenine.co.uk/glossary/electromotive-force-emf)
- [current](https://www.gradenine.co.uk/glossary/current)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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-torch-contains-three-identical-cells-430b55ff) · Published by Druglandscape Ltd.