Question

Can any one tell me something about the topic
ROOT MEAN SQUARE (RMS) or VIRTUAL VALUE OF AC

Answer 1

It is that steady value of current means d.c that will produce the same amount of heat in a given resistance in a given time as is done by a.c for the same time in the same resistance.

Answer 2

Electrical engineers often need to know the power, P, dissipated by an electrical resistance, R. It is easy to do the calculation when there is a constant current, I, through the resistance. For a load of R ohms, power is defined simply as:

P = I^2 R.\,\!

However, if the current is a time-varying function, I(t), this formula must be extended to reflect the fact that the current (and thus the instantaneous power) is varying over time. If the function is periodic (such as household AC power), it is nonetheless still meaningful to talk about the average power dissipated over time, which we calculate by taking the simple average of the power at each instant in the waveform or, equivalently, the squared current. That is,

P_\mathrm{avg}\,\! = \langle I(t)^2R \rangle \,\! (where \langle \ldots \rangle denotes the mean of a function)
= R\langle I(t)^2 \rangle\,\! (as R does not vary over time, it can be factored out)
= (I_\mathrm{RMS})^2R\,\! (by definition of RMS)

So, the RMS value, I_\mathrm{RMS}, of the function I(t) is the constant signal that yields the same power dissipation as the time-averaged power dissipation of the current I(t).

Answer 3

Thanks to you both