An electric motor operating on a 60 volt D.C supply draws a current of 10 amp. If the efficiency of the motor is 50%, the resistance of its windings is

Options

(a) 3 ohm
(b) 6 ohm
(c) 15 ohm
(d) 30 ohm

Correct Answer:

3 ohm

Explanation:

Efficiency n = 50 %

e = E/2 ⇒ I = (E – e) / R = [E – (E/2)] / RA = E / 2R

10 = 60 / 2R ⇒ R = 60 / (2 × 10) = 3 ohm