Average Power In Ac Circuit — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Average Power in AC Circuit Applicable to all AC circuits (LCR, pure R, pure L, pure C) under steady-state sinusoidal conditions. Instantaneous power p(t) = V(t) I(t) = Vm sin(wt) Im sin(wt - phi). Using trigonometric identity: sin(A)sin(B) = 0.5[cos(A-B) - cos(A+B)]. Integrate instantaneous power over one period T (0 to 2 pi/w). The term involving cos(2wt - phi) integrates to zero over a full cycle. Resulting P avg = (Vm Im / 2) cos(phi), which simplifies using RMS relations. Assumes sinusoidal voltage and current waveforms. Voltage and current must have the same frequency. The value of cos(phi) is limited between 0 and 1. Assuming power is simply V I as in DC circuits; in AC, the phase relationship matters. Confusing peak power with average power; peak power is twice the average power in resistive circuits. Thinking inductors and capacitors consume average power; in ideal cases, they consume zero average power (Wattless current).