A.C. and D.C.

A.C. and D.C.

Direct Current

  • Direct current (DC) refers to the flow of electric charge in a single direction.
  • Batteries or cells provide a good example of a DC source since they have a positive and negative terminal and current always flows in the same direction.
  • Devices such as torches, cars and most portable devices use DC.
  • While most electronic devices require DC to operate, they often include a power supply component to convert AC from the mains to DC.

Alternating Current

  • Alternating current (AC) is a type of electrical current in which the direction of the flow of electrons switches back and forth at regular intervals or cycles.
  • The UK mains electricity supply is a good example of AC, where the current changes direction 50 times per second (50Hz).
  • AC is used for mains electricity because it is easier to generate and is more efficient to transmit over large distances.

Comparing AC and DC

  • AC and DC have different characteristics and uses. DC is constant and travels in one direction, useful for low-voltage applications and electronics. But DC can’t be easily transmitted over long distances.
  • AC is variable, changing direction and amplitude (size), enabling it to travel long distances, making it ideal for power supply systems. However, most electronic devices must convert AC to DC to operate.
  • Transformers are devices that change the voltage of AC. They are used widely in the power network to step up the voltage for transmission and step down the voltage for domestic use.

Conversion between AC and DC

  • A device called a rectifier is used to convert AC to DC. This is often seen in power supplies for electronic equipment.
  • An inverter is used to convert DC to AC, which is used in solar power systems or electric vehicles.

Safety Aspects

  • Touching a live AC mains circuit can result in a lethal electric shock because the current can cause muscles to contract, making it impossible to let go of the live conductor.
  • DC can also cause an electric shock, but since it does not lead to muscle contraction in the same way AC does, it is less likely to lead to a lethal incident as the current can be let go. However, both AC and DC can be dangerous and should be treated with caution.