Please differentiate between v(rms) and V(avg/dc) of an Ac signal . Why do we use rms and why is vrms called effective value; why is vp not so called or (v(avg))? And why we use v rms to calculate power (avg)?
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1$\begingroup$ Why we use V rms to calculate average power? Because it gives the right answer! I'm sorry, I don't know the mathematical explanation of why it gives the right answer, but giving the right answer is the reason why we use it. $\endgroup$ – Solomon Slow Oct 5 '15 at 12:07
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1$\begingroup$ Possible duplicate of Justification of root mean square $\endgroup$ – Kyle Kanos Oct 5 '15 at 12:43
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2$\begingroup$ See also physics.stackexchange.com/q/41779 and physics.stackexchange.com/q/146113 $\endgroup$ – Kyle Kanos Oct 5 '15 at 12:44
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The average voltage of a pure AC signal is 0V. That's not a lot of use.
Vrms is widely used because it ensures that an AC voltage produces the same heating effect in a resistor as the equivalent DC voltage. This also means it will produce the same light from an incandescent lamp.
