ABSTRACT
In Eq. (7-96) let's consider voltage ei as an input which produces current i as output. The quantity (ifeJ(D) is the admittance and its sinusoidal version is given by
If ei = E sin wt,
(7-102)
The instantaneous power varies cosinusoidally around its average value at a frequency 2w, just twice the frequency of the impressed voltage (and the resulting current). During any one cycle, power flows into the circuit from the source for a portion of the time and is returned to the source from the circuit the rest of the time. Average power is that which is actually "used up" by the circuit and is what the electric company charges for. The angle ¢ by which the current leads the voltage is called the power factor angle, and cos¢ is called the power factor. In general, the angle ¢ may be "leading" (between oo and +90°) or "lagging" (between 0° and -90°); thus the power factor is between 0 and 1.
