The simplest cases of sinusoidal power sources supplying purely resistive and purely reactive loads have been discussed.
In these cases, the load is expressed by a real or a pure imaginary number.
In general, the load is represented by a complex quantity (the impedance value).
In this case, load impedance can be represented by its equivalent circuit (e.g., a pure resistance and a pure reactance in series).
With this representation in mind, the electric power dissipated in the load ZL (Figure 3.3) can be expressed by the sum of power components separately dissipated by resistance REQ and reactance XEQ of the equivalent circuit ZL.