Question

The average power absorbed by an impedance Z = 30 – j 70 Ω when a voltage V = 120∠0° is applied is _____________

(a) 35

(b) 37.24

(c) 45

(d) 50.25

This question was addressed to me during an online interview.

Origin of the question is Advanced Problems on Magnetically Coupled Circuits topic in chapter Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

Right choice is (b) 37.24

To explain: The current through the impedance is given by,

I = \(\frac{V}{Z} = \frac{120∠0°}{30-j70}\)

= \(\frac{120∠0°}{76.16∠-66.8°}\)

= 1.576∠66.8° A

The average power is, P = 0.5VmImcos (θv – θi)

= 0.5(120) (1.576) cos (0 – 66.8°)

= 37.24 W.