How Many Volts IS ThisHow Many Volts IS This? The RMS Role Douglas Brooks Let’s start the explanation of why with a discussion of power. Power is defined as Voltage*Current ( or P=V*I). By Ohm’s Law, V=I*R, or I=V/R. Therefore, by substitution, Power=V2/R. So if we apply a voltage sine wave (V*sin(Q)) across a resistor, the power applied to the resistor is given by the expression P=V2*sin2 (Q)/R (shown in Figure 1(b)). It can be shown that the average power delivered to the resistor is V2/2*R. Now here is the key question. What DC (direct current) voltage will deliver the SAME power to the resistor as the AC waveform we have just been considering? The answer is: Equivalent DC Volts = (V2/2).5 = .707*V. THIS is defined as the RMS voltage. It is the DC voltage that would deliver the SAME power to a resistive load……