1. Recall and use the equations P = IV and E = IVt

Power is a measure of how quickly energy is transferred. The unit of power is the watt, W. The more energy that is transferred in a certain time, the greater the power of the appliance. It is calculated using the formula:

power = current * voltage
P= I * V

where P=power, I=current and V=voltage/p.d. This can be rearranged to find the current and voltage if the other two values are given.
I = P ÷ V
V = P ÷ I

In an earlier unit, we learned that power = energy ÷ time. Rearranging it with energy as the subject, we get energy = power * time. We now know that power = current * voltage. So, energy can be written as:

energy = current * voltage * time
E = IVt


Notes submitted by Lintha

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