Question

Calculate the value of resistance if total heat dissipated is 78 W when 5 A current flows through it.

(a) 3.12 Ω

(b) 2.24 Ω

(c) 1.45 Ω

(d) 5.13 Ω

I have been asked this question during an interview.

This intriguing question comes from Induction Motors in section Speed Control of Direct Current Motors & Induction Motors of Electric Drives

Answer 1

Correct answer is (a) 3.12 Ω

The best I can explain: 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 0°. R=P÷I^2=3.12 Ω.