We know that the voltage and current vary sinusodially with time in AC circuits.The "equivalent" values in a DC circuit are called the "rms values" and are given by

or

where V

_{rms}and I_{rms}are the rms values of the voltage and the current and V_{o}and I_{max}are themaximumvalues of the voltage and the current.Both v(t) and i(t) vary sinusodially -- as the sine function (or cosine function). That means their

mean valueiszero. So taking just theirmeanvalue would be meaningless. A useful alternate is to take the mean value of thesquare. The mean value of the square of the sine (or cosine) is one-half,The square

rootof themeanof thesquareof a sine function is one over the square root of two,That is why these are called

rmsvalues and that is where the constant comes from .(c) Doug Davis, 2002; all rights reserved

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