試題詳解

20. Consider a purely resistive heater connected to an AC power source (rms voltage 120 V, frequency 60 Hz) with an average heating power of 1 kW. If an inductor is connected in series with the heater, causing the average heating power to drop to 1/4 of its original value, what is the phase angle between the voltage and the current?
(A) 15°
(B) 30°
(C) 45°
(D) 60°
(E) 90°