What is the phase angle of the impedance for a network formed by a 400-ohm inductor reactance in parallel with a 300-ohm resistor?

• A. -36.9 degrees
• B. 36.9 degrees
• C. 53.1 degrees
• D. -53.1 degrees

Answer: (B)

The phase angle of the equivalent impedance tells you how much the network behaves like an inductor (positive angle) or a capacitor (negative angle). For a parallel combination, you find the overall impedance by combining the individual impedances.

Here, the inductive reactance is j400 ohms and the resistor is 300 ohms. Use the parallel formula Z_eq = (Z_L Z_R) / (Z_L + Z_R). This gives Z_eq = (j400 × 300) / (300 + j400) = (j120000) / (300 + j400). Simplifying by multiplying top and bottom by the complex conjugate (300 − j400) yields Z_eq = 192 + j144 ohms.

The phase angle is arctan(Im(Z_eq) / Re(Z_eq)) = arctan(144 / 192) ≈ 36.87 degrees, about 36.9 degrees. The positive angle confirms the network is more inductive at this frequency.