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Home > Physics > Using electricity > Alternating and direct current


Alternating and direct current


This revision bite will take you through the subject areas: battery and mains supplies, symbols and circuits, charge and current, and voltage and energy.

Work through them all or go to the ones that interest you. You may wish to print a hard copy for your reference.

Battery and mains supplies

Cells, batteries and the mains supply are all sources of electrical energy. There are some important differences between them that you should know about:

The signal is a flat line at 1.5V

Direct current

Cells and batteries supply direct current (dc). This means that the current is always in the same direction in a circuit.

  • The mains supply is alternating current (ac). This means that the current from a mains supply constantly changes direction in a circuit.
  • The frequency of the mains supply is 50 hertz (50 Hz).
  • The declared value of the mains supply in Britain is 230 volts (230 V).
  • Credit Level only. The current is always changing direction with the mains supply because the voltage is always changing. The peak value of an alternating voltage is greater than the declared value. This can be seen on the sketch graph.
Wave-form graph demonstrating that the peak value of an alternating voltage is greater than the declared voltage

Video: Direct current vs alternating current

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Diagram of a wire with the plastic insulation stripped back to reveal the three metal wires within.

Class Clips

Video clip about conductors and insulators.

Watch this video clip to learn more about voltage and current:

Voltage and current


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