Question

In a DC series motor, if the armature current is halved, the torque of the motor will be equal to

(a) 100% of the previous value

(b) 50% of the previous value

(c) 25% of the previous value

(d) 10% of the previous value

This question was posed to me in final exam.

I'm obligated to ask this question of Operating Characteristics of DC Series Motor -1 in portion Characteristics of DC Motors of DC Machines

Answer 1

Right choice is (c) 25% of the previous value

Explanation: Torque in the case of linear magnetization of DC series motor is directly proportional to square of the armature current. So, armature current is made 1/2th of the original value, then torque will be 1/4th of the original value.