Current

Alternating and direct current

An electric current flows either as a direct current or as an alternating current.

Direct current

An oscilloscope screen displaying the signal from a direct current (DC) supply. It is a horizontal straight line at 1.5V.

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A direct current flows in one direction only.

On a voltage-time graph this would appear as a straight horizontal line at a constant voltage.

Car batteries, dry cells and solar cells all provide a direct current (dc) that only flows in one direction.

An oscilloscope screen displaying the signal from an alternating current (AC) supply. It is a 50Hz sine wave that peaks at 230V.

Alternating current

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An alternating current regularly changes direction.

On a voltage-time graph, this would appear as a curve alternating between positive and negative voltages - the positive and negative values indicate the direction of current flow.

Power stations produce electricity using generators. They generate an alternating current (ac). In the UK, the mains electrical supply is at a frequency of 50 Hertz (Hz) and is delivered to houses at 230 Volts (V).