Electrical Energy (Cambridge (CIE) O Level Physics): Revision Note

Electrical Energy Equation

• Everyday appliances transfer energy from the mains supply to the appliance

  • For example, a heater will transfer energy electrically 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

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)