From the instant of start-up, through the acceleration period, and until the motor reaches rated speed, when is the counter EMF produced in the windings of a DC motor 'zero'?

Correct Answer: Option B — armature is not yet turning

Counter electromotive force (CEMF) in a DC motor is generated by armature conductors cutting magnetic lines of force as the rotor turns. From start-up until the armature actually begins to rotate, the rotational speed is zero, meaning CEMF is likewise zero, resulting in high initial inrush current.