We use electricity to heat and light our homes. Electrical energy transferred is calculated by multiplying current, voltage and time.

Electricity meters measure the number of units of electricity used in a home or other building. The more units used, the greater the cost. The cost of the electricity used is calculated using this equation:

For example, if 5 units of electricity are used at a cost of 8p per unit, the total cost will be 5 × 8 = 40p.

Remember that the number of units used can be calculated using this equation:

Units (kWh) = power (kW) × time (h)

Total cost = power (kW) × time (h) × cost per unit

- Question
An electric fire needs 2 kW. It is switched on for 3 hours. If each kWh costs 10p, how much does it cost to run the fire?

Cost = power × time × cost of 1 kWh

= 2 kW × 3 h × 10p

=

**60p**

- Question
A TV needs 250 W. It is switched on for 30 minutes. If each kWh costs 8p, how much does it cost to run the TV?

Cost = power × time × cost of 1 kWh

= 0.250 kWh × 0.5 h × 8p

=

**1p**