Which of these is not a common part of a DC motor?

• A. Magnets
• B. Commutator
• C. Brushes
• D. Wood insulating block

Answer: (D)

DC motors rely on a magnetic field, a rotating armature with windings, and a way to switch current as the rotor turns. Magnets (or electromagnets) provide the stationary field in which the armature spins. The armature carries windings and sits on a shaft inside the magnetic field. A commutator and brushes work together to reverse the current in the armature windings as the rotor turns, keeping torque in the same direction and enabling continuous rotation. A wood insulating block isn’t a standard part because motors require materials that remain stable under heat, moisture, and mechanical stress; wood can swell, warp, or burn, and it isn’t as reliable an electrical insulator or mechanical support as the plastics, resins, mica, and laminations typically used.