1. Buying electricity

2. Calculating the units of electricity The amount of electrical energy (i.e. the amount of electricity) used by an appliance depends on its power and how long the electricity is used for. electrical energy = power x time Power is measured in kilowatts (kW) and the time is measured in hours (h) so what are the units of electricity measured in? 1 unit of electricity = 1 unit of electrical energy = 1 kilowatt hour (kWh) Example: How many units of electricity is 17.6 kWh? 17.6 units

3. How is electricity paid for? Electricity costs money which is why every home has an electricity meter. The meter records how much electricity is used in a house in units of electrical energy. The units of electrical energy are called kilowatt hours (kWh). The cost of an electricity bill is calculated from the number of units used.

4. How much does electricity cost? The cost of electricity is the number of units of electrical energy multiplied by the cost per unit. cost = number of units x cost per unit Example: How much would 10 units of electricity cost at a price of 9p per unit? cost = 10 units x 9 p/unit = 90 p

5. Buying electricity - example A kettle uses 45.2 kWh of energy. If electricity costs 10p per unit, how much does it cost to use the kettle? Number of units: number of units of electricity = number of kilowatt hours = 45.2 units Cost of electricity: cost = number of units x cost per unit = 45.2 units x 10 p / unit = 452p or £4.52

6. Buying electricity - example An iron that operates at a power of 3kW for 4 hours uses electricity that costs 8p per unit. How much does it cost for the electricity used by the iron in that time? Number of units: number of units of electricity = number of kilowatt hours = 3 kW x 4h = 12 units = 12 kWh Cost of electricity: cost = number of units x cost per unit = 12 units x 8p / unit = 96p

7. Buying electricity calculations