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 plotting current or voltage against time for direct current, the line would be horizontal.

Steady direct current is ideal for electronic circuits and is typically supplied by batteries or a regulated power supply. All battery-operated devices use DC. Some examples of useful things that rely on batteries are:

  • Electric vehicles
  • Mobile phones
  • Flashlights

This also includes devices that use an AC adapter when plugged into the wall.

Alternating current

An alternating current (AC) is an electric current that reverses direction at regular intervals.

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

Alternating current is used for long-distance energy transmission because it can be transferred more efficiently

In the UK, the mains electricity supply operates at a frequency of 50 Hz with a potential difference of 230 V. This means the voltage fluctuates between +230 V and -230 V, causing the current to change direction 50 times per second.

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