Direct Current and Alternating Current

An electric current can either be a direct current or an alternating current.

Direct current

A direct current (DC) is an electric current that constantly flows in only one direction, at a constant voltage. On a graph that shows current or voltage against time for a direct current, it would appear as a horizontal line.

Steady direct current is ideal for electronic circuits, typically in batteries or a regulated power supply. Everything that runs on a battery relies on DC. Some examples of useful things that rely on batteries are:

  • Electric vehicles
  • Mobile phones
  • Flashlights

As well as anything that uses an AC adapter when plugged into the wall.

Alternating current

An alternating current is an electric current that reverses direction at regular intervals. It flows back and forth around a circuit.

On a graph that plots current or voltage against time for an alternating current, it will alternate between positive and negative values. This shows the direction that the current flows.

An alternating current is necessary to transfer energy efficiently across countries. In the UK, the mains electricity supply has a frequency of 50 Hz and a potential difference of 230 V. This means that the current fluctuates between +230 V to -230 V and the current changes direction 50 times per second.