electricity at home

• Mains electricity


  Electricity can flow either as direct or alternating current, and is used in homes to power electrical appliances
• National Grid


  Distributes electricity throughout the country
• Plug


  • Connects a device to the mains electricity supply
  • Cable between the device and the three-pin plug contains three copper wires coated with plastic
  • Copper wires are good conductors
  • Plastic is a good insulator
• Parts of a plug

  • Outer insulation
  • Cable grip
  • Live wire
  • Fuse
  • Neutral wire
  • Earth wire
• Outer insulation


  All three wires in the cable are bundled together and there is extra plastic insulation wrapped round them all for safety
• Cable grip


  Holds the cable tightly in place so that wires do not become loose
• Live wire


  Copper wire coated with brown plastic along which the current enters the device
• Fuse


  A glass or ceramic canister containing a thin wire that melts if the current gets too high
• Neutral wire


  Copper wire coated with blue plastic that also connects to the cable in the wall and completes the circuit
• Earth wire


  Copper wire coated in striped plastic that provides a path for current to flow from the case of the device to the ground if there is a fault
• Without the earth wire, if a fault occurs and the live wire becomes loose


  There is a danger that it will touch the case and the next person who uses the appliance could get electrocuted
• Earthing


  The earth wire is connected to the case and is attached to a metal plate or water pipe underground, providing a low resistance path to the ground
• Fuse


  Provides a built-in fail-safe to the electrical circuit for a device, containing a thin wire that will melt if the current gets too high
• If there is a fault that causes the casing of the device to become live

  A large current will flow through the low-resistance earth wire, causing the fuse to melt and breaking the circuit
• Electricity can flow either as direct or alternating current, and is used in homes to power electrical appliances
• The National Grid distributes electricity throughout the country
• Electrical appliances


  Appliances that transfer energy from one store to another, for example chemical energy in the fuel in power stations to kinetic energy in a fan or heat energy in a cooker
• Energy transferred by an appliance

  Depends on the power (energy transferred each second) and the amount of time the appliance is switched on for
• Calculating energy transferred by an appliance

  Energy = power × time
• One watt is the power when one joule of energy is transferred in one second
• Time should be converted from minutes into seconds by multiplying the number of minutes by 60
• Calculating energy transferred by a 1,500 W hair dryer in 15 minutes

  • Energy = 1,500 × (15 × 60) = 1,350,000 J or 1.35 megajoules (MJ)
• Calculating power of an appliance

  Power = potential difference × current
• When working with mains electricity and appliances, the potential difference is 230 V
• Calculating power of an electric heater drawing 8 amps

  • Power = 230 × 8 = 1,840 W
• Calculating energy transferred by the 1,840 W electric heater in 20 minutes

  • Energy = 1,840 × (20 × 60) = 2,208,000 J or 2.21 MJ