Page 133 - York Global Science 6 - Physical Science

Physical Science

may need a lot of power but only for a short time. Other appliances may not
need much power but may be used for a longer time.

Electricity companies sell electrical energy in units called kilowatt-hours
(kWh). A kilowatt-hour is a unit of measurement.
1 kWh is the amount of energy a 1000 W appliance uses in an hour.

If you have 1 kWh of energy, you can use a 100-watt lightbulb for 10 hours or a
2000-watt oven for 30 minutes.

100 W 2000 W

Worked Example
If you have an appliance that needs 2000 W of power to work and you use it

for 2 hours, you would be using 4 kWh of energy.
To work out how many kWh an appliance uses, you must change watts to

kilowatts by dividing by 1000 and then multiply this by the time in hours.

2000 watts = 2 kW 100 watts = 0.1 kW
2 kW × 2 hours = 4 kWh 0.1 kW × 2 hours = 0.2 kWh

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