Power in AC Circuits

Because both the voltage and the current vary continuously with time in an AC circuit, the ordinary DC notion of power (a fixed value) does not directly apply; instead, power must first be defined at a single INSTANT and then AVERAGED over a complete cycle to give a meaningful, practically usable measure. This section derives that average-power formula, introduces the idea that part of an AC current can carry zero net power at all (the wattless current), defines the power factor that ties these ideas together into a single des …