# A engineer is designing a circuit for a new electric vehicle charging station. One charging port uses a motor with a high resistance, and a second charging port uses a motor with a lower resistance. Both motors are connected in parallel to the same power supply, so the potential difference across each motor is identical. Explain why the motor with the lower resistance transfers energy at a greater rate than the motor with the higher resistance, when both are connected to the same potential difference.

> OCR A-Level Physics A (H556) — 3.3 Work, energy and power · Explain · 5 marks

> Both motors are connected in parallel to a power supply, so the potential difference across each motor is the same. The two motors have different resistances.

## Mark scheme (5 marks)

1. Power is the rate at which energy is transferred (power = current × voltage / P = IV)
2. With the same potential difference, the motor with lower resistance allows a greater current to flow
3. A greater current means greater power is transferred (linking larger current to larger power at the same voltage)
4. Therefore the lower-resistance motor transfers more energy per second / has a higher power output
5. Energy transferred also equals charge × potential difference (E = QV) or energy = power × time (E = Pt), linking back to why more current means more energy transferred over the same time

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-engineer-is-designing-a-circuit-049ba73b) · Published by Druglandscape Ltd.