Question 248Electricity & Electronics - QMED

The correct answer is D) motor is at rated speed. The counter EMF (electromotive force) of a DC motor is maximum when the motor is running at its rated speed. This is because the counter EMF is directly proportional to the speed of the armature. As the motor reaches its rated speed, the armature rotates at its maximum velocity, generating the highest possible counter EMF. The other options are incorrect because: A) the counter EMF is lower when the armature is not turning; B) the counter EMF increases as the motor approaches its rated speed, but is not yet maximum; and C) the counter EMF is lower when the armature has just begun to turn and is not yet at its maximum speed.