# A rechargeable electric bicycle motor transfers energy to the wheels. The motor operates at a potential difference of 36 V and draws a current of 15 A. Explain how the concepts of power and energy transfer apply to this motor, and describe what happens to the rate of energy transfer if the current drawn by the motor doubles while the potential difference stays the same.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.3 Work, energy and power · Explain · 5 marks

> An electric bicycle uses a rechargeable battery to power a motor. The motor is connected to the battery and drives the rear wheel. The motor operates at a potential difference of 36 V and draws a current of 15 A during normal riding.

## Mark scheme (5 marks)

1. Power is the rate at which the motor transfers energy
2. Power equals current multiplied by potential difference (P = IV)
3. The motor's power is 540 W (correct calculation: 15 × 36)
4. If the current doubles (to 30 A), the power also doubles (to 1080 W)
5. Greater power means energy is transferred to the wheels at a faster rate / more energy transferred each second

## Key terms

- [power](https://www.gradenine.co.uk/glossary/power)
- [potential difference](https://www.gradenine.co.uk/glossary/potential-difference)
- [current](https://www.gradenine.co.uk/glossary/current)
- [energy](https://www.gradenine.co.uk/glossary/energy)
- [rate](https://www.gradenine.co.uk/glossary/rate)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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-rechargeable-electric-bicycle-motor-transfers-697498fe) · Published by Druglandscape Ltd.