# Power

## What is Power?

The quantity power is the rate at which work is done. The quicker work is done the greater the power. The standard metric unit of power is the Watt. The calculation of power is the work done in Joules divided by a unit of time seconds. 1 Watt is equivalent to 1 joule of work done per second. Many machines have their power rating displayed upon them in Watts, the higher the value the greater the power of the machine and the faster the rate of energy transfer.

## Power equation

To calculate Power we write the equation like this.

$P = { W \over \text{t}} = { E \over \text{t}}$

## Power demo

In this tutorial you will learn how to calculate the power the rate of doing work during an energy transfer.

## Chilled practice question

Calculate the power of an electric fire if it transfers 950 KJ of energy in 5 minutes 30 seconds.

## Frozen practice question

An electric heater has a power rating of 2200 W. How long to the nearest second does it take to give out 500 KJ of energy.

## Science in context

Power is the rate of energy transfer per second

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