# 4.2.11 Electrical Working

### Electrical Energy

• As electricity passes around a circuit, energy is transferred from the power source to the various components (which may then transfer energy to the surroundings)
• As charge passes through the power supply it is given energy
• As it passes through each component it loses some energy (transferring that energy to the component) The current transfers electrical energy from the power source and to the components

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### Calculating Electrical Energy

• The amount of electrical energy used by a component or appliance depends upon three things:
• The current
• The potential difference
• The amount of time the device is used for
• The energy transferred can be calculated from the equation:
`energy transferred = current × potential difference × time`
`E = I × V × t`
• Where the unit of energy is the joule (J)

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### Electrical Power

• Power is the rate of energy transfer (the amount of energy transferred per second)
• The power of an electrical component (or appliance) is given by the equation:
`Power = Current × potential difference`
`P = I×V`
• 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)
• Note that the above equation is related to the equation for energy – after all, power is just energy per second, and so:
```energy transferred  =  power × time  =  current  ×  potential difference  ×  time

```

#### Exam Tip

Remember: Power is just energy per second.

“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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