As electricity is all about energy, there are a few energy and power equations that you need to be able to derive and use...

The definition of voltage tells us that

So, W = VQ

The definition of current tells us that, Q = It

So, W = V I t (Learn this!)

Of course, we already know that:

So, Power = V I (Learn this!)

From Ohm's law we know that V = IR. If this equation is substituted into the equation P = IV we can get two new equations:

Power = I²R

or

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Electrical energy is measured in units of the kWhr so that people can be charged for the amount that they use. At the moment, 1 kWhr of energy costs about 7p.

energy = power x time

kWhr = kW x hr