GCSE Physics · AQA 8463 · Topic 4.2.3
Domestic uses and safety
Key points
- Direct current (d.c.) flows one way only (cells, batteries). Alternating current (a.c.) keeps reversing direction.
- UK mains electricity is a.c. at a frequency of 50 Hz and a p.d. of about 230 V.
- A three-core cable has a live wire (brown, about 230 V), a neutral wire (blue, about 0 V) and an earth wire (green and yellow, 0 V).
- The earth wire is a safety wire: it only carries current if there is a fault, stopping a metal case becoming live.
- The live wire is dangerous even when a switch is off, because touching it makes a large p.d. between it and your body (at earth potential), so current flows through you.
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Batteries and the mains supply both push charge round circuits, but in different ways. This sub-topic explains the difference, what the three wires in a plug cable do, and why even a switched-off light fitting can still give you a dangerous…
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