Which type of motor is brushless by design?

• A. AC induction motor
• B. DC motor
• C. Universal motor
• D. Stepper motor

Answer: (A)

Brushless by design means there’s no mechanical commutation on the rotor. An AC induction motor fits this because its rotor is driven by the rotating magnetic field created by the stator’s AC windings, usually a simple squirrel-cage rotor with no brushes or commutator. As a result, it operates without any sliding contacts, making it inherently brushless. The DC motor and universal motor rely on a commutator and brushes to switch current as the rotor turns, so they are not brushless by design. Stepper motors are typically driven by electronic control and are also brushless in their common form, but the classic, most straightforward example of a motor that is brushless by design among these options is the AC induction motor.