Question

Calculate the total cost a using a 100 W lamp and a 300 W hair dryer for 10 minutes if a unit of electricity is 14p.

For the lamp:

Number of units used = power rating in kW x time in hours

Power rating = 100 W =

time = 10 minutes =

Number of units used = 0.1 kWh x 0.167 h = 0.0167 kWh

total cost = number of units used × cost per unit

= 0.0167 kWh x 14p

= 0.23p

For the hair drier:

Number of units used = power rating in kW x time in hours

Power rating = 300 W =

time = 10 minutes =

Number of units used = 0.3 kWh x 0.167 h = 0.0501 kWh

total cost = number of units used × cost per unit

= 0.0501 kWh x 14p

= 0.70p

Total cost = 0.23p + 0.70p = 0.93p

The cost of using the lamp and hair dryer is 0.93p.

Question

A TV needs 250 W. It is switched on for 30 minutes. If each kWh costs 14p, how much does it cost to run the TV?

Number of units used = power rating in kW x time in hours.

Power rating = 250 W =

Time = 30 minutes =

Number of units used = 0.25 kWh x 0.5 h = 0.125 kWh

Total cost = number of units used × cost per unit

= 0.125 kWh x 14p

= 1.75p

The cost of running the TV is 1.75p