Practice question

**Wattless current** occurs in pure inductor or capacitor, I_rms non-zero but average power zero because φ=±90°, cos φ=0, energy oscillates between source and field, no dissipation, used in choke coil to limit current without heating, unlike resistor where power dissipated. Z = √(R² + (X_L - X_C)²) = √(50² + (80 - 60)²) = √(2500 + 400) = √(2900) ≈ 53.85 Ω . Power factor: cos Φ = (R/Z) = (50/53.85) ≈ 0.928 . Applying X_L = ωL, X_C = 1/ωC, Z = √(R² + (X_L - X_C)²), I_rms = V_rms/Z, P = V_rms I_rms cosφ, V_s/V_p = N_s/N_p, calculation gives 0.928, consistent with phasor