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What are direct and alternating currents ?

If the current flows in only one direction it is called direct current, or d.c. Batteries and cells supply d.c. electricity, with a typical battery supplying may be 1.5V. The diagram shows an oscilloscope screen displaying the signal from a d.c. supply.

If the current constantly changes direction, it is called alternating current, or a.c.. Mains electricity is an a.c. supply, with the UK mains supply being about 230V. It has a frequency of 50Hz (50 hertz), which means it changes direction, and back again, 50 times a second. The diagram shows an oscilloscope screen displaying the signal from an a.c. supply.


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