# Mains electricity

In the UK, mains electricity is alternating current (a.c.) at 230 V and 50 Hz. The current keeps reversing direction. A battery gives direct current (d.c.), which flows one way.

Physics (school) · Part 07: Mains electricity and magnetism · Card 2 of 8 · Last updated 2026-10-19

## Analogy

Mains is like a person pushing and pulling a saw back and forth. A battery is like pushing one way only.

## In practice

Wall sockets supply a.c. Phones and laptops use a charger to turn it into d.c.

## Practice

### Flashcards

- **What is the mains voltage and frequency in the UK?** 230 V and 50 Hz.

### Interview questions

**A hairdryer is rated 1,150 W and works on 230 V mains. Work out the current and choose a fuse from 3 A, 5 A and 13 A.**

- I = P / V = 1,150 / 230 = 5 A
- Fuse must be just above the working current
- A 5 A fuse would blow in normal use
- Choose a 13 A fuse

## Questions people ask

### What is the difference between a.c. and d.c.?

Direct current (d.c.) flows in one direction, as it does from a battery. Alternating current (a.c.) reverses direction many times a second. UK mains reverses 50 times each second, which is a frequency of 50 Hz. An oscilloscope shows d.c. as a flat line and a.c. as a wave.

### Why is mains electricity dangerous?

A voltage of 230 V can push a current through the body that is high enough to stop the heart or cause burns. Water lowers the body's resistance, making a shock worse. Never use electrical devices near water, and never push anything into a socket.

## Related concepts

- [Plug wires and fuses](https://studyvisually.com/learn/science/physics-school/physics-school-part-7/physics-school-part-7-concept-3)
- [Static electricity](https://studyvisually.com/learn/science/physics-school/physics-school-part-7/physics-school-part-7-concept-1)
- [Earth wire](https://studyvisually.com/learn/science/physics-school/physics-school-part-7/physics-school-part-7-concept-4)
- [Motor effect](https://studyvisually.com/learn/science/physics-school/physics-school-part-7/physics-school-part-7-concept-7)

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