Practice question

**Power factor** cos φ = R/Z, 0≤cos φ≤1, at resonance cos φ=1 maximum power, pure L or C cos φ=0 zero average power, current wattless because energy stored returned. Instantaneous power when current maximum in pure L: I=I_peak, V=0 because V leads 90°, so P= V I =0 at that instant, average zero. Maximum power dissipation in a series LCR circuit occurs at resonance, where X_L = X_C , making the impedance equal to the resistance ( Z = R ). At this point, the power factor ( cos Φ ) is 1, and power ( P = I² R ) is maximized. Applying X_L