# 1.7.6 Power

### Power, Work Done & Time Taken

• Machines, such as car engines, transfer energy from one form to another every second
• The power of a machine is the rate at which the machine transfers energy
• The greater the rate at which energy is transferred, the greater the power

Two identical cars accelerating to the same final speed will both gain the same amount of energy. But if one of them reaches that speed sooner, it will have a greater power

• Because work done is equal to energy transferred, the power is also equal to the rate of doing work

Extended Only

### Calculating Power

• Power is the amount of energy transferred (or work done) every second.
• Power, work and time are related by the following equation:

• You can rearrange this equation with the help of the formula triangle:

• The unit of power is the watt (W), which is the same as a joule per second (J/s)

#### Exam Tip

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

### Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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