mains supply and national grid

• describe direct current

  one direction current flow produced by direct potential difference
• describe alternating current

  changing direction current flow produced by alternating potential difference
• describe mains supply

  alternating current of 230V and 50Hz
• give wires in mains supply connections

  live, neutral and earth
• describe live wire

  brown wire providing alternating potential difference at 230Hz
• describe neutral wire

  blue wire that completes circuit at 0V
• describe earth wire

  green and yellow wire that stops appliance becoming live at 0V
• describe affect of connections between live wire and earth

  creates potential difference allowing current flow through an electric shock
• describe national grid

  system of transformers and cables connecting power stations and consumers to transfer electrical power
• give pathway of electrical power in national grid

  1. power station
  2. step up transformer
  3. step down transformer
  4. consumer
• describe function of step up transformer

  increase potential difference and decrease current from power station to cables
• describe function of step up transformers

  decrease potential difference and increase current from cables to consumers
• describe efficiency of national grid

  minimise energy lost to thermal store of surroundings through heated up wires from high current