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Electrical quantities

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When an electric current flows through a circuit we can measure the current and potential difference. From this it is possible to calculate power. The cost of electricity depends upon the amount of electrical power used, the amount of time it's in use for, and the charge made for each unit of electricity. It is possible to reduce heat losses from homes using insulation - this saves money - but some methods of insulation are more cost-effective than others.

# Current and potential difference

You need to know how to measure the current that flows through a component in a circuit. You also need to know how to measure the potential difference, also called voltage, across a component in a circuit.

## Current

A current flows when an electric charge [electric charge: The electrical state of an object, which can be positively charged or negatively charged. ] moves around a circuit – measured as the rate of flow of charge. No current can flow if the circuit is broken, for example, when a switch is open. Click on the animation to see what happens to the charge when the switch is opened or closed.

### Measuring current

• current is measured in amperes - often abbreviated to amps or A
• The current flowing through a component in a circuit is measured using an ammeter [ammeter: A device used to measure electric current. ]
• the ammeter must be connected in series with the component.

## Potential difference (voltage)

A potential difference, also called voltage, across an electrical component is needed to make a current [current: Moving electric charges, for example, electrons moving through a metal wire. ] flow through it. Voltage is the electrical pressure that gives a measure to the energy transferred. Cells or batteries often provide the potential difference needed.

### Measuring potential difference

• Potential difference is measured in volts, V
• Potential difference across a component in a circuit is measured using a voltmeter
• The voltmeter must be connected in parallel with the component.

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