# Electricity generated at a power station is transmitted across the country through the National Grid. Explain why electricity is transmitted at very high voltages, and describe the role of transformers in making the National Grid both efficient and safe for domestic use.

> Edexcel A-Level Physics (9PH0) — 13.1 Simple harmonic motion and damping · Explain · 5 marks

> A power station generates electricity at 25 000 V. Before the electricity enters the National Grid, a transformer increases this to 400 000 V. At the other end of the transmission lines, close to towns, another transformer reduces the voltage before it enters homes.

## Mark scheme (5 marks)

1. Transmitting at high voltage reduces the current in the power cables
2. A lower current in the power cables means less energy is lost as heat (thermal energy) in the cables, making transmission more efficient
3. A step-up transformer is used to increase the voltage (and reduce the current) before electricity enters the transmission lines
4. A step-down transformer is used near homes / towns to reduce the voltage to a safer, lower level for domestic use
5. Transformers require alternating current (AC) to work, because AC produces a continuously changing magnetic field in the primary coil, which induces a current in the secondary coil

## Key terms

- [National Grid](https://www.gradenine.co.uk/glossary/national-grid)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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/electricity-generated-at-a-power-station-724c4966) · Published by Druglandscape Ltd.