Define RMS & average value as applied to A.C. voltage & current

Root mean square value (RMS value)

It is that value of d.c. current which when flowing through a given circuit for a given time produces the same heat as produced by the alternating current when flowing through the same circuit for the same time.

RMS value in terms of voltage:

where, Vm – maximum voltage

The mean of the squares of the instantaneous values of voltage over one complete cycle (T).

Mean or Average value

The average value of an alternating current is that dc current which transfers across any circuit the same charge as is transferred by that alternating current during the same time. Average value can be calculated as

But, average value of a symmetrical alternating waveform is always zero because it has equal negative and positive values. hence average value over a complete cycle is zero. We will calculate average value for half cycle.


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