Kilowatt-hour

Key Stage 3

A kilowatt-hour is a unit of energy used for electrical appliances and in electrical bills.

The kilowatt-hour is used by electricity suppliers instead of Joules.

A kilowatt-hour is calculated by multiplying the power rating of an appliance in kilowatts by the time the appliance is used for in hours.

A kilowatt-hour is 3,600,000 Joules.

The amount of energy an appliance uses depends on the power rating and how long the appliance is used for.

Energy usage for appliances is measured in kilowatt-hours. This means all power ratings need to be in kilowatts and time should be in hours.

Energy can be calculated with the equation: Energy = Power x time

The Power ratings of some electrical appliances.
Filament Bulb A 60Watt filament bulb may be used for 8 hours a day. Calculate the energy in kilowatt-hours.	Energy Saving Bulb A 25Watt energy saving bulb may be used for 8 hours a day. Calculate the energy in kilowatt-hours.	Kettle A 2000Watt kettle may be used for 30 minutes a day. Calculate the energy in kilowatt-hours.
Power = 60W = 0.060kW Time = 8 hours Energy = Power x time Energy = 0.060 x 8 Energy = 0.48kilowatt-hours	Power = 25W = 0.025kW Time = 8 hours Energy = Power x time Energy = 0.025 x 8 Energy = 0.20kilowatt-hours	Power = 2000W = 2.0kW Time = 30 minutes = 0.5hours Energy = Power x time Energy = 2.0 x 0.5 Energy = 1.0kilowatt-hours
Television A 250Watt television is left on for 3 hours each day. Calculate the energy in kilowatt-hours.	Refrigerator A 200Watt refrigerator is on for 24 hours each day. Calculate the energy in kilowatt-hours.	Oven A 2500Watt oven is used for 45 minutes each day. Calculate the energy in kilowatt-hours.
Power = 250W = 0.25kW Time = 3 hours Energy = Power x time Energy = 0.25 x 3 Energy = 0.75kilowatt-hours	Power = 200W = 0.20kW Time = 24 hours Energy = Power x time Energy = 0.20 x 24 Energy = 4.8kilowatt-hours	Power = 2500W = 2.5kW Time = 45 minutes = 0.75 hours Energy = Power x time Energy = 2.5 x 0.75 Energy = 1.875kilowatt-hours