Power in an AC (Alternating Current) circuit is a measurement of voltage (E) multiplied by the current (A) , if the load is purely a resistive load. Through a resistive load the voltage and current are in phase. Inductive (L) or capcitive (C) loads produce a phase shift in the current. These shifts are called lead or lag. In a capcitive circuit the current leads the voltage by a quarter shift. Likewise the current through an inductor lags the voltage by a quarter shift. True AC power measurements must factor these phase shifts into the measurement. Power is expressed in watts (W)
Power in a DC (Direct Current) circuit is a measurement of voltage (E) multiplied by the current (A) and is expressed in watts (W).