Question

How does an electric motor use magnetic force to produce motion?

The north pole of a permanent magnet placed in the center of an electromagnet attracts the north pole of the electromagnet.
The north pole of an electromagnet placed in the center of a permanent magnet attracts the north pole of the permanent magnet.
The north pole of a permanent magnet placed in the center of an electromagnet repels the north pole of the electromagnet.
The north pole of an electromagnet placed in the center of a permanent magnet repels the north pole of the permanent magnet.

Answer 1

Short answer about the four choices: 3 and 4 are correct. Like magnetic poles (north–north or south–south) repel; unlike poles attract.

How an electric motor uses that to make motion (brief):
- A current in a coil produces a magnetic field, so the coil becomes an electromagnet (its polarity depends on current direction).
- That electromagnet sits in the fixed magnetic field of permanent magnets or another set of coils (the stator).
- The fields interact: opposite poles attract and like poles repel, producing forces and a torque on the rotating part (the rotor or armature).
- In a DC motor a commutator (or electronic switching in brushless motors) reverses the current in the coil at the right times so the rotor always experiences a torque in the same rotational direction. In more advanced motors the same effect is achieved by timed switching of currents in multiple coils.
- More fundamentally, the motor’s force comes from the Lorentz force on the current-carrying conductors (F = I L × B), which is the microscopic origin of the attraction/repulsion picture.

So the key idea: switchable electromagnet polarity creates alternating attraction/repulsion with the permanent magnets (or other coils), producing continuous rotation.