Energy Transfers in Appliances (Edexcel GCSE Physics)

• Everyday appliances transfer energy electrically from the mains supply to the appliance
  • For example, in a heater, energy is transferred to the thermal store of the heating element

• The amount of energy an appliance transfers depends on:
  • The time 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

• As charge (electrons) flows around a circuit, energy is transferred from the power source to the various components 
  • As the electrons pass through the power supply, energy is transferred to the electrons
  • As the electrons pass through each component, energy is transferred from the electrons to the components

The flow of charge transfers energy from the power source to the components

• Different domestic appliances transfer energy electrically from the chemical store of the DC cells and batteries, such as a remote control
• Most household appliances transfer energy electrically from the AC mains supply
• The energy can be transferred to the kinetic store 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, the energy can be transferred to the heating element of 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

• The power of an appliance is the amount of energy it transfers by electrical work every second

• Every electrical appliance has a power rating, which tells you how much energy it needs to work

• The power rating for domestic electrical appliances is normally given on a label
• This will include:
  • The potential difference required  (eg. 230 V in the UK)
  • The frequency of the supply (eg. 50 Hz in the UK)
  • The power rating in Watts (this varies for each device)

• The higher the power rating, the quicker the change in stored energy
  • For example, a 2000 W kettle means the kettle transfers 2000 J of energy per second from one store to another

• The different power ratings of various household appliances are listed in the table below as examples:

Power Ratings Table

• Care must be taken not to plug an appliance into a mains that is has a voltage that is much higher than stated on the label, for example in another country that has a higher mains voltage
  • This could cause the appliance to fuse or set fire and become damaged

Mains electric appliances, such as this kettle, are fitted with labels that list important information such as the power and voltage of the appliance