Electrical Energy (CIE IGCSE Physics)

• Everyday appliances transfer electrical energy from the mains to other forms of energy in the appliance
  • For example, in a heater, this will transfer electrical energy into a thermal energy store

• The amount of energy an appliance transfers depends on:
  • How long the appliance is switched on for
  • The power of the appliance

• A 1 kW iron uses the same amount of energy in 1 hour as a 2 kW iron would use in 30 minutes
• A 100 W heater uses the same amount of energy in 30 hours as a 3000 W heater does in 1 hour

Calculating Electrical Energy

• To calculate electrical energy use the equation

• Where:
  • E = energy (joules, J)
  • V = voltage (volts, V)
  • I = current (amps, A)
  • t = time (seconds, s)

• As electricity passes around a circuit, energy is transferred from the power source to the various components (which may then transfer energy to the surroundings)
  • As charge passes through the power supply it is given energy
  • As it passes through each component it loses some energy (transferring that energy to the component)

The current transfers electrical energy from the power source and to the components

• Different domestic appliances transfer energy from batteries, such as a remote control
• Most household appliances transfer energy from the AC mains
• This can be to the kinetic energy of an electric motor. Motors are used in:
  • Vacuum cleaners - to create the suction to suck in dust and dirt off carpets
  • Washing machines - to rotate the drum to wash (or dry) clothes
  • Refrigerators - to compress the refrigerant chemical into a liquid to reduce the temperature

• Or, in heating devices. Heating is used in:
  • Toasters - to toast bread
  • Kettles - to boil hot water
  • Radiators - hot water is pumped from the boiler so the radiator can heat up a room

Energy transfers for a washing machine and toaster