P2- Mains electricity

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alternating current

  • cells and batteries supply current that passes round a circuit in one direction
  • this is direct current
  • current from a mains supply passes in one direction then reverses and passes in the other direction 
  • this is alternating current
  • mains supply= 50 hertz, changes direction 50 times each second- volts is 230v
  • live wire alternates between positive +325v and negative -325v  potential creating a pd of 230v
  • neutral wire stays at zero
  • frequency=1/time

cables and plugs

  • electrical appliances are normally connected to the mains electricity via cable and three pin plug
  • out cover of plug is made of plastic or rubber as both are good electrical insulators
  • pins are made of brass because brass is a good electrical conductor, its hard and doesnt oxidise
  • earth wire- longest pin and is green and yellow
  • live wire- brown wire
  • neutral wire- blue wire
  • a two core cable doesnt have an earth wire
  • in a plug the cable grip should be secure to prevent wires becoming loose or exposed
  • appliances with metals cases must be earthed so they do not become live and create electric shocks
  • appliances with plastic cases do not need to be earthed…


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