Physics - 5 - Mains electricity

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Alternating current

  • Direct current is in one direction only. Alternating current repeatedly reverses its direction.
  • The peak voltage of an alternating potential difference is the maximum voltage measured from zero volts
  • A mains circuit has a live wire that is alternately positive and negative every cycle and a neutral wire at zero volts
  • To measure the frequency of an a.c. supply, we measure the time period of the waves the use the formula: frequency =   1/time taken for 1 cycle
  • Mains electricity is an alternating current(ac) supply. An alternating current repeatedly reverses its direction. It flows one way then the opposite way in successful cycles. Its frequency is the number of cycles it passes through each second

Cables and plugs

  • Sockets and plug cases are made of stiff plastic materials that enclose the electrical connections. Plastic is used because it is a good electrical insulator
  • Mains cable consists of two or three insulated copper wires surrounded by an outer layer of flexible plastic material
  • In a three-pin plug or a three-core cable, the live wire is brown, the neutral wire is blue, and the earth wire is green and yellow
  • The earth wire is connected to the longest pin and is used to earth the metal case of a mains appliance
  • When you plug in a heater with a metal case into a wall socket, you 'earth' the metal case automatically. This stops the metal case becoming 'live' if the live wire breaks& touches the case. If the case did become live&you touched it, you would be electrocuted


  • A fuse contains a thin wire that heats up, melts, and cuts off the current if the current…


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