Chapter 7, Problem 37R

To determine

To Describe: The device.

Explanation of Solution

Introduction: An electric motor is a machine which transforms electrical energy into mechanical energy.

A simple electric motor comprises of a wire coil, a battery and a permanent magnet. The flow of current in the coil makes it an electromagnet.

The motor also includes components such as brushes and a commutator. The brushes connected to the battery act as conducting pads. The brushes make contact with the commutator, which is a split metal ring. The commutator’s each half is connected with one end of the coil & so the commutator is able to rotate with the coil. The brushes and the commutator along with the battery and the coil forms a closed circuit.

When a current flow in the coil, the magnetic force between the coil and permanent magnet causes the coil to rotate.

The coil rotates until it reaches a position where the brushes line up with the gaps in the commutator and is not in contact with it anymore, due to which, there is neither current in the coil nor magnetic forces are exerted on the coil. The coil’s inertia keeps it rotating.

The coil has rotated such that the brushes are again in contact with the commutator. However, the direction of the current in the coil is reversed by the commutator. This flips the poles of the magnetic field around the coil.

The coil rotates till its poles are besides the permanent magnet’s opposite poles. The current is reversed by the commutator again, and the coil keeps rotating. The entire cycle repeats and the coil will rotate as long as the battery stays connected. Thus, electrical energy is converted into mechanical energy.