To find a useful metric, we calculate the $P$, defined as the average of the instantaneous power over one period. $$P = \frac1T \int_0^T p(t) , dt$$ Alexander and Sadiku derive the final form as: $$P = \frac12 V_m I_m \cos(\theta_v - \theta_i)$$ Where $\theta_v - \theta_i$ is the phase difference between voltage and current. This value represents the actual power consumed by the resistive elements of the circuit (measured in Watts, W).
The Alexander-Sadiku series is known for linking theory to real-world scenarios. Interesting examples related to early chapters and Chapter 11 include: circuiti elettrici alexander sadiku pdf 11
The 11th edition includes a "Computer Tools" section in every chapter. Download a free copy of (not PSpice, which is expensive). Recreate the circuit diagrams from the PDF inside LTspice. Seeing the waveform on a graph will cement your understanding. To find a useful metric, we calculate the