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Domestic energy

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Energy transfer

Energy transfers can be calculated with the below formula:

Energy transfer

The power (W) can come from the power rating of the item, and this means the amount of energy transferred every second. Therefore, the energy transfer can be calculated for appliances in the home.  

Both joules and watts can also be in kilojoules (kJ) or kilowatts (kW) if the number is large. To do this, divide the joules or watts by 1000.  

Unit conversion


1. A 850 W washing machine takes 1 hour to wash one load. What will be the energy transfer in kilojoules?   

- First, convert 1 hour to seconds: There are 60 minutes in an hour and 60 seconds in a minute.

60x60=3600 seconds in an hour. 

- Then, time in seconds (s) can be multiplied with the power rating to work out the energy transferred. 

850 W x 3600 s = 3,060,000 J 

 - The energy transfer is 3,060,000 J. This can be converted to kilojoules (kJ) by dividing by 1000.  

3,060,000 J / 1000 = 3,060 kJ



Complete the 10 energy transfer problems below.