Electric Motors

An electric motor is a device that uses an electromagnet to turn an axle. Figure 11 shows how an electric motor works. In this figure, the wire is connected to a battery. An actual motor has many loops of wire around a central iron core to make the motor stronger. In the motor of an electric appliance, the wire would be connected to an electrical circuit in a building.

Figure 11A battery supplies current to a loop of wire through the commutator. As the commutator turns, the direction of current switches back and forth. As a result, the coil's magnetic field keeps switching direction, and this turns the coil about an axle. Predicting What would happen if you reversed the positive and negative connections on the battery?

d

What makes a motor turn? When current flows through a loop of wire, one side of the loop is pushed by the field of the permanent magnet. The other side of the loop is pulled. These forces rotate the loop. If there were no commutator ring, the coil would come to rest. But as the loop turns, each C-shaped half of the commutator connects with a different brush, reversing the current. The forces now change direction, so the coil continues to rotate. As long as current flows, rotation continues.

Table of Contents