If the output of an ac generator is connected to a resistor, an alternating current will flow. An ac generator generates a voltage and an EMF with the shape of a sine or cosine curve.
The power is given by the product of voltage and current, so the power will have the shape of a
curve.
The RMS voltage is given by the square root of the average of the voltage squared:
Likewise the RMS current is given by the square root of the average of the current squared:
The RMS power is given by the product of the RMS voltage and the RMS current:
When ac values for current, voltage or power are being quoted, they are the rms values.