Ac and DC supply

DC that is Direct Current

Many of the things we use at home need a DC supply but the supply to our houses is AC, so what's the difference?

Oscilloscope attached to dry cells to show how DC trace is obtained
Oscilloscope attached to dry cells

A cell or a battery (a group of cells) supply direct current. If we connect a battery to an oscilloscope we can see a graph of the change in potential difference (voltage) with time. The graph we see is a horizontal line. The potential difference is steady and in one direction. If the battery is connected to a circuit a steady current will flow in one direction.

DC trace on oscilloscope is a flat line
DC trace on oscilloscope

AC that is Alternating Current

If we connect it to an oscilloscope to the live and neutral of a mains supply to see a graph of potential difference (voltage) plotted against time then the graph rapidly moves up and down. The potential difference changes from one direction to the other many times per second in a sinusoidal pattern. In the UK there are 50 complete changes every second (50Hz).

AC trace on an oscilloscope is a sine curve with a wave time of 1/50 th of a second
AC trace on an oscilloscope

The potential difference is applied to the live wire. The current is “pushed and pulled” from the live wire, the neutral wire completes the circuit.Live and neutral attached to a hair drier to show where an oscilloscope can measure

Other useful pages about mains electricity supply are: