# 5.1.4 Power

### Defining Power

• The power of a machine is the rate at which it transfers energy
• Since work done is equal to the energy transferred, power can also be defined as the rate of doing work or the work done per unit time
• The SI unit for power is Watts (W) where 1 W = 1 J s-1

Power is the rate of change of work

• You may be familiar with labels on lightbulbs which indicate their power such as 60 W or 100 W. These tell you about an energy transferred by an electrical current rather than by a force doing work

### Solving Problems Involving Power

#### Exam Tip

Think of power as “energy per second”. Thinking of it this way will help you to remember the relationship between power and energy: “Watt is the unit of power?”

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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