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.

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

Explanation:

The commutator of the electric motor reverses the current in each half revolution to keep the torque, turning the coil in the same direction. This occurs as the north pole of the electromagnet nears the south pole of the permanent magnet, and the current reverses, which causes the poles of the magnets to repel.

Thus, the correct answer is "the north pole of an electromagnet placed in the center of a permanent magnet repels the north pole of the permanent magnet".