Question

Which function is performed by counter emf of a DC motor?

(a) Exceeds supply voltage

(b) Aids applied voltage

(c) Helps in energy conversion

(d) Regulates its armature voltage

This question was posed to me during an internship interview.

I'm obligated to ask this question of DC Motor Basics -2 topic in portion DC Motors of DC Machines

Answer 1

Right choice is (c) Helps in energy conversion

To explain I would say: Back emf or counter emf makes the DC a self-regulating machine i.e. it makes the DC motor to draw as much armature current as it is just enough to develop the required load torque. Thus, it helps in energy conversion and it is always less than applied voltage.