3H - Cost of electricity

Having already established that the kilowatt-hour is the unit of energy that we use to pay for our electricity, we went through how to calculate the cost of electricity used. This can be a bit confusing because we have to convert our power rating to kilowatts and our time to hours - this is really the opposite of what we normally do.

There are two types of calculation; the first is just an E=Pt calculation which we have done before but we have to use kilowatts instead of Watts and hours instead of seconds. If we do use Watts and seconds we'll get the answer in Joules which will be a really big number! The second type of calculation is where the cost is taken into account. Here all you do is multiply the number of units (this is the same as saying the number of kilowatt hours) by the price per unit which will always be given in the question.