Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Did you know?

We also have Bitesize study guides covering many subjects at National 4 and National 5 on our Knowledge & Learning BETA website.

Home > Physics > Using electricity > Alternating and direct current

Physics

Alternating and direct current

Back

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

In order to see this content you need to have both Javascript enabled and Flash installed.

 

Back

Watch

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

Play

A picture of Mia Cadaver

Tombstone Timeout

Test out your knowledge of physics with Mia Cadaver's physics game - it's serious fun!

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.