Obviously using a new super duper large plasma
screen T.V is going to use more electricity than using a small 5” pocket black
and white T.V. The formula below shows us how to calculate the number of
units that has been used – and it all depends on the power rating of the
appliance.
Units = power x time
(kwh)
Kw x hour
We will trick
you!!! Your exam
questions will not be
this straight forward –
you will be expected to
convert the units given
to you into the units
needed in the formula!
See opposite for help
1. To convert watts to kilowatts divide by 1000.
2. To convert kilowatts to watts multiply by 1000.
3. To convert minutes to hours divide by 60.
4. To convert hours to minutes multiply by 60.
You will need a calculator
Questions.
How many units will a 200w toaster use if it is on for 6 hours?
How many units will an 8kw shower use in 20 minutes?
How many kilowatt hours will a 60w lightbulb use if it is left on
for two days?
How many units will a 500w hoover in a week if it is used once
a day for 2 weeks, and 30 minutes per use?
Electrical = power x time
Energy j
w
s
Ht only – make sure
you become
familiar with using
this formula in
revision classes!!!