DC and AC supply

• Direct current (DC)


  Current that only flows in one direction
• Alternating current (AC)


  Current that constantly changes direction
• The main benefit of using AC is that it's very easy to use a transformer to increase or decrease the potential difference
• In the UK, AC switches direction 50 times per second, so it has a frequency of 50 Hertz
• In the UK, AC has a potential difference of around 230 volts
• Oscilloscope trace for AC

  • Shows the potential difference rising and falling, indicating the current going backwards and forwards
  • The height of the peaks shows the maximum potential difference, which is around 230 volts in the UK
• Oscilloscope trace for DC


  • The potential difference does not change
• Using an oscilloscope trace to calculate AC frequency

  1. The time between two consecutive peaks shows one complete cycle

  2. The frequency is the number of cycles per second, calculated as 1 divided by the time for one cycle