Mains Electricity — AC and DC

This lesson covers alternating current (AC), direct current (DC) and the UK mains electricity supply, including the three-pin plug and electrical safety, as required by AQA GCSE Combined Science Trilogy (8464, section 6.2.2).

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AC vs DC

Property	Direct Current (DC)	Alternating Current (AC)
Direction of flow	Always in one direction	Repeatedly reverses direction
Source	Cells, batteries, DC power supplies	Mains supply, generators
Oscilloscope trace	Flat horizontal line	Sine wave
UK mains?	No	Yes

Why Does the UK Use AC?

The main reason the UK mains supply uses AC is that AC can be easily transformed (stepped up or down) to different voltages using a transformer. This is essential for the efficient transmission of electricity through the National Grid (covered in a later lesson).

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The UK Mains Supply

Property	Value
Voltage	~230 V
Frequency	50 Hz