Alternating current (AC)



Alternating current or emf is the one whose magnitude varies with time and direction reverses periodically. The current in the circuit supplied with alternating emf is called AC and the circuit itself is called AC circuit.

The instantaneous value of ac is given by:

current-1

 

and

current-2

 

Where I0 and E0 are the peaks value of alternating current and emf called amplitudes.

If f be the frequency then we have;

W=2πf and f=1/T where T is the time period of AC.

 

Advantages of ac

  • Generation, transmission and distribution of AC is economical and easier than that of DC.
  • AC can be easily converted into DC by a rectifier.
  • AC can be controlled more easily by using a choke coil.
  • AC can be transmitted from one place to another by the use of a transformer.
  • AC instruments are stronger and easier to use.

Disadvantages of ac

  • AC is very dangerous because of its attractive nature and also because it’s maximum or peak value is √2 times its effective or average value.
  • AC cannot be used in the electrolysis process such as electroplating, electro refining, electro typing. These processes strictly demand DC.
  • The distribution of AC in the conducting wire is not uniform. The concentration of the current is more on the surface of the wire and less in the body of wire. This effect is called screen effect.
  • Marking on the AC scales is not uniform or equidistant.