If we plot sine θ against θ we get a *sine wave* - this graph shows just one cycle but it repeats every 360°.

Sine waves occur a lot in Nature, and the voltage and current in an alternating current circuit are sine waves.

From this picture we can easily see that the area of the graph above the θ axis is exactly the same as that under it, so that over one complete cycle the mean (“average”) θ, and therefore also the voltage and current, are all zero.

However, as described earlier on this Page, the heat produced by a resistor is I² × R, which is positive whether I is positive or negative, so the *heat* produced over one complete cycle is *not* zero.

The sum of the values in the third column is 6 and the number of values is 12 so the

Similarly for rms

© Barry Gray August 2017