Lesson 5 of 9

Power and the cost of energy

Goal: Calculate the cost of running an appliance.

Puzzles for this lesson

Power is how quickly an appliance transfers energy. It is measured in watts (W).

A 100 W television transfers 100 J every second. A 2000 W heater transfers energy twenty times as quickly.
1 kilowatt (kW) = 1000 W. So the power of the heater is 2 kW.
Electricity bills count energy in kilowatt hours (kWh). 1 kWh is the energy that a 1 kW appliance transfers in one hour.

cost = power (kW) × time (hours) × price (per kWh)

Your turn

This lesson’s activity starts here in a moment.

I can say what power in watts means.I can use cost = power × time × price.

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Power How quickly energy is transferred, in watts

Kilowatt hour The energy a 1 kW appliance transfers in one hour

For teachers: AQA 3.3.1