# A bicycle dynamo produces electricity to power the bike's lights. Inside the dynamo, a small magnet rotates near a coil of wire. Explain why an alternating current (a.c.) is produced in the coil, and describe two ways the cyclist could increase the size of the induced voltage.

> Eduqas A-Level Physics — 4.5 Electromagnetic induction · Explain · 5 marks

> A bicycle dynamo contains a permanent magnet that spins inside a coil of wire when the wheel turns. The faster the wheel turns, the faster the magnet rotates.

## Mark scheme (5 marks)

1. As the magnet rotates, the magnetic field through the coil continuously changes direction / the field lines cut the coil in opposite directions on each half-turn
2. This changing magnetic field induces a voltage / current in the coil (electromagnetic induction)
3. Because the field direction reverses each half-turn, the induced voltage / current reverses direction each half-turn, producing alternating current
4. First method to increase induced voltage: increase the speed of rotation of the magnet (cycle faster / increase wheel speed)
5. Second method to increase induced voltage: use a stronger magnet OR increase the number of turns on the coil

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level 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-bicycle-dynamo-produces-electricity-to-545818e5) · Published by Druglandscape Ltd.