# differentiate between v(rms) and V(avg/dc) of an Ac signal [duplicate]

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)?

• 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. – Solomon Slow Oct 5 '15 at 12:07
• Possible duplicate of Justification of root mean square – Kyle Kanos Oct 5 '15 at 12:43
• – Kyle Kanos Oct 5 '15 at 12:44

## 1 Answer

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.