Question

Calculate the active power in a 1.2 Ω resistor with 1.8 A current flowing through it.

(a) 3.88 W

(b) 3.44 W

(c) 3.12 W

(d) 2.18 W

I got this question during an interview for a job.

This question is from Energy Relations During Starting in portion Starting of Electric Drives

Answer 1

Right choice is (a) 3.88 W

Explanation: The resistor is a linear element. It only absorbs real power and dissipates it in the form of heat. The voltage and current are in the same phase in case of the resistor so the angle between V & I is 90^o. P=I^2R=1.8×1.8×1.2=3.88 W.