Question

The armature current in D.C motor is maximum when the motor has -
A. picked up maximum speed
B. just started
C. intermediate speed
D. just been switched off

Answer 1

Hint: We know that DC motors take electrical power through direct current, and convert this energy into mechanical rotation. DC motors use magnetic fields that occur from the electrical currents generated, which powers the movement of a rotor fixed within the output shaft. DC motors are suitable for many applications including conveyors, turntables and others for which adjustable speed and constant or low-speed torque are required. They also work well in dynamic braking and reversing applications, which are common in many industrial machines.

Complete step by step answer
We know that as the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as Er = Eb.
We can say that back electromotive force (back EMF, BEMF) is a voltage that appears in the opposite direction to current flow as a result of the motor's coils moving relative to a magnetic field. It is this voltage that serves as the principle of operation for a generator.
Motor e.m.f. equation $E_{b}=V-I_{a} R_{a}$
At starting $E_{b}=0,$ so $I_{a}$ will be maximum.
So we can say that the armature current in a D.C motor is maximum when the motor has just started.

Hence the correct answer is option B.

Note: We can say that electromotive force, abbreviation E or emf, energy per unit electric charge that is imparted by an energy source, such as an electric generator or a battery. Energy is converted from one form to another in the generator or battery as the device does work on the electric charge being transferred within itself. In electricity generation, a generator is a device that converts mechanical energy to electrical energy for use in an external circuit. The source of mechanical energy may vary widely from a hand crank to an internal combustion engine. Generators provide nearly all of the power for electric power grids.