Direct and alternating current, mains

The idea

Cells and batteries supply direct current (dc), which flows in one direction. Mains electricity is an alternating current (ac) supply that repeatedly changes direction; in the UK it has a frequency of 50 Hz and a potential difference of about 230 V. Most appliances use three-core cable: the live wire (brown) carries the alternating potential difference, the neutral wire (blue) completes the circuit at about 0 V, and the earth wire (green and yellow stripes) is a safety wire that only carries current if there is a fault.

1. Separate dc (one direction) and ac (changes direction).
2. Know the UK mains values.
3. Name each wire's colour and job.

Watch out The live wire is dangerous even when a switch is off, because it is still at 230 V.