A D.C. motor makes use of a commutator to change the direction of current in the coil.

Introduction:
A commutator is a device used in DC motors to change the direction of the current flowing in the coil. It consists of a rotating cylinder with metal segments and brushes that make contact with these segments. When the commutator rotates, the brushes make contact with different segments, reversing the direction of the current in the coil. This reversal of current direction is crucial for the operation of a DC motor.

Explanation:
The commutator is primarily used in DC motors, and its function is to change the direction of the current flowing in the coil. This change in current direction is essential for the motor to continue rotating in a single direction. Let's understand why the commutator is necessary for DC motors.

DC Motors:
A DC motor operates using direct current (DC) as its power source. In a basic DC motor, there is a coil placed within a magnetic field. When current flows through the coil, it experiences a force due to the interaction between the magnetic field and the magnetic field produced by the current in the coil. This force causes the coil to rotate.

However, in order to keep the coil rotating in a single direction, the direction of the current in the coil needs to be reversed periodically. This is where the commutator comes into play.

Role of the Commutator:
The commutator in a DC motor serves two main purposes:

1. Reversing Current Direction: The commutator ensures that the current flowing through the coil changes direction periodically. This is achieved by the brushes on the commutator making contact with different segments as the commutator rotates. As a result, the current flowing in the coil is reversed, allowing the motor to continue rotating in a consistent direction.

2. Maintaining Torque: The commutator also helps maintain the torque produced by the motor. Torque is the rotational force that enables the motor to do work. By reversing the current direction in the coil, the commutator ensures that the torque remains constant and the motor continues to rotate smoothly.

Conclusion:
Therefore, the correct answer is option 'C' - a commutator changes the direction of current in a DC motor. It is an essential component that allows the motor to operate efficiently and maintain a consistent rotational motion.

B is right