What is the primary role of brushes in a DC motor?

The primary role of brushes in a DC motor is to create torque. In a DC motor, brushes are used to conduct current from the power supply to the rotating armature, allowing the magnetic field produced by the current to interact with the magnetic field of the stator. This interaction generates a force on the armature, which is what produces torque and causes the motor to rotate. The torque generated is directly related to the strength of the magnetic fields and the amount of current flowing through the armature windings.

While other options may relate to various aspects of motor operation, they do not directly reflect the fundamental function of brushes. For instance, controlling speed involves varying the voltage or adjusting the amount of current in a separate manner, which does not depend solely on the presence of brushes. Stabilizing rotation may refer to balancing or maintaining the conditions under which the motor operates, but it is not a direct responsibility of the brushes. Reducing noise can be a result of using certain materials or designs in the motor construction, but it is not the intrinsic purpose of brushes in the electrical and mechanical interaction within a DC motor.