Question

A direct current (DC) motor is connected to a battery through two leads. The motor moves for slightly less than half the cycle and comes to halt. Which of the following components is missing?
A) One of the brushes
B) Commutator
C) Slip ring
D) One of the two magnets

Answer 1

Hint: A DC motor is a device that is used to convert direct current electrical energy into mechanical energy. It is used to refer to any rotary electrical machine. These can vary in size and power from small motors to large mechanisms.

Complete solution:
A commutator consists of a cylinder which is composed of the multiple metal contact segments on the rotating armature of the device. It is a rotary electrical switch that reverses the current direction between the rotor and the external circuit. The commutators are used to reverse the polarity of the current in the armature windings of DC motors.
A slip ring is used to transfer the power between the rotating structure and the stationary structure of an AC machine. It is a continuous ring. When the power is supplied from the AC generator to the AC motor, a slip ring is used. In DC motors, when the current has to change the direction for every half revolution, slip rings are used. Thus when the slip rings are not present, then the armature comes to halt by stopping its rotation.

Hence the correct option is C.

Note: 1. Slip rings are used in many industrial automatic applications and also for some of the types of equipment like cable and hose winders, tower and jib cranes, etc.
2. Split rings are used for reversing the direction of the current. These are used in DC Machines.
3. A commutator is a segmented one whereas the slip ring is continuous.