Question

which best compares a brush and a commutator in an electric motor?
both rotate when the motor is on.
both carry electrical current from a power source.
both remain stationary when the motor is on.
both have a permanent magnetic field.

Explanation:

To solve this, we analyze the components of an electric motor:

• A brush in an electric motor is stationary and makes contact with the commutator to transfer current from the power source.
• The commutator is part of the rotating armature but also helps in carrying the electrical current (by reversing the current direction, but still involved in current transfer from the power source via the brushes).
• Option 1 is wrong because brushes are stationary. Option 3 is wrong because the commutator (part of the armature) rotates. Option 4 is wrong as neither the brush nor the commutator has a permanent magnetic field (the permanent magnets or electromagnets in the motor's field structure do, not these components). So the correct option is the one stating both carry electrical current from a power source.

Answer:

B. Both carry electrical current from a power source.