# A farmer uses an electric fence controller to keep livestock in a field. The controller is connected to the mains supply and transfers energy to the fence wire. Explain how the concepts of potential difference, current, and power are related in determining the rate at which the controller transfers energy to the fence wire.

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

> An electric fence controller is rated at 230 V and draws a current of 0.5 A from the mains supply. The controller is left running continuously to deter animals from crossing the fence boundary.

## Mark scheme (5 marks)

1. Potential difference is the energy transferred per unit charge (between two points in the circuit)
2. Current is the rate of flow of electrical charge (through the fence wire/circuit)
3. Power is the rate at which energy is transferred (by the controller)
4. Power equals current multiplied by potential difference (P = IV)
5. A greater power means the controller transfers energy to the fence wire at a faster rate (linking all three quantities to energy transfer rate)

## Key terms

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

## 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-farmer-uses-an-electric-fence-72283b4f) · Published by Druglandscape Ltd.