Current

Alternating and direct current

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

An oscilloscope screen displaying the signal from a direct current (DC) supply. It is a horizontal straight line at 1.5V.A direct current flows in one direction only

Direct current

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.In an alternating current the direction of charge movement regularly changes

Alternating current

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 usually provide an alternating current (ac). In the UK, the mains electrical supply is generated at a frequency of 50 hertz (Hz) and is delivered to houses at about 230 volts (V).