# A bicycle dynamo generates electricity to power a front lamp. The dynamo works by rotating a permanent magnet inside a fixed coil of wire. A cyclist increases their speed, causing the magnet to rotate more quickly. Explain how the dynamo produces a voltage and why the voltage increases when the magnet rotates more quickly.

> Pearson Edexcel International GCSE Physics (4PH1) — 6.3 Electromagnetic induction · Explain · 4 marks

> A bicycle dynamo consists of a small permanent magnet that spins inside a fixed coil of wire when the wheel turns. When the dynamo is connected to the bicycle lamp, the lamp glows. As the cyclist pedals faster, the lamp becomes noticeably brighter.

## Mark scheme (4 marks)

1. There is relative motion / movement between the (rotating) magnet and the coil, so the magnetic field through the coil changes.
2. This changing magnetic field induces a voltage in the coil (generator effect).
3. When the magnet rotates more quickly, the magnetic field through the coil changes more quickly / at a faster rate.
4. The greater the rate of change of the magnetic field, the greater the induced voltage, so the voltage (and brightness of the lamp) increases.

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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