Some important points about alternating current

  • The total power carried by an alternating current is calculated using a root mean square formula.This is because of the fact that the average value of a sine wave equals zero if we average over an integral number of cycles.Instead we square the sinewave, average it,and then take the squareroot of that average.Squaring first makes the negative halves of the sinewave add to the average.

The advantages of using alternating current are many.

  1. Its voltage can be changed using transformers which are over 95% efficient.
  2. Induction motors which run on AC are much more long lasting and maintenance free compared with universal motors.
  3. The cycling nature of the AC makes sure that any spark generated in mechanical switching devices do not last longer than a very tiny fraction of a second.DC switches are much more prone to sparking and contact pitting.
  4. Polarity reversal need not cause immense damage as it can with DC.
  5. An alternator powered by a rotating power source (wind / water turbine or engine) can use slip rings intead of brushes which again give them the advantages that induction motors have.