What’s apparent about ‘apparent power’?

Where do the terms “apparent power” and “apparent efficiency” come from? What’s the difference between “apparent” and “real”?

In d-c circuits, power is always “real,” measured only in watts equal to the product of volts and amperes. In an a-c circuit, this holds true only in a pure resistance; when any inductance or capacitance is present, current and voltage are out of phase with each other, and power in watts is less than their product. Volts times amperes in the a-c circuit is called “apparent” power only because that product is in the same units that do represent watts in the pure resistance. “Apparent efficiency” of an inductive device such as a motor is the product of the true efficiency (power output divided by watts input) and the power factor (which accounts for the phase displacement). 

Source: Electrical Apparatus

NOTA: Este texto está relacionada con la publicación 'Resistencia del Alambre Conductor Vs. Resistencia del Aislamiento' publicada el 15 de julio, 2014.