Engineering & Technology


What is power?

Power is the measure of how quickly energy is transferred.

Often electrical energy is transferred into other forms such as heat, light and magnetism.

An electrical appliance such as a kettle converts electrical energy into heat energy and it does so at a rate dependent on its power. A standard kettle might have a power rating of 2000 Watts (2 kW) and will bring the water to the boil within a certain period of time. A kettle with a power rating of 1000 Watts (1 kW) would take twich as long however.

The basic formula for calculating power is:

P is the power in Watts (W)
I is the current in Amperes (A)
V is the voltage in Volts (V)

The Power Triangle

The power triangle is a way of remembering the power formula and how to transpose it to find an unknown quantity.

If you want to make P the subject, cover up the  P and the result is P = I x V.
If you want to make I the subject cover up the I and the result is I = P/V.
If you want to make V the subject cover up the V and the result is V = P / I

Other ways of calculating power

There are two other formulae we can use to calculate power. These two formula are derived from P=IV and Ohm's law. I've shown how these two formulae are derived just so you can see where they come from.

Where this comes from:

Where this comes from: