Students know the role of electromagnets in the construction of electric motors, electric generators, and simple devices, such as doorbells and earphones.

As noted in the California Science Framework (page 58), electromagnets may be thought of as magnets that can be turned on or off. By connecting an electric circuit, the electromagnet can be turned on resulting in the motion of some internal part of a bell, a speaker, or a motor. The internal part could be a metal, a permanent magnet, or another electromagnet within the electrical device.

The diagram below shows one way that a fire alarm can be set up. Note that the flow of electricity causes an electromagnet to attract the hammer part of the bell. This makes the ringing noise. However, when the hammer moves to hit the bell, it simultaneously moves away from a wire terminal and thereby disconnects the circuit. This means the electromagnet will turn off, and the hammer will spring back to its original location. This springing back reconnects the circuit, reactivating the electromagnet, and making the hammer move to hit the bell again. Thus, as long as the fire alarm switch is closed, the electromagnet keeps turning on and off, and the alarm bell keeps ringing.

An electric motor uses this same idea of having one or more electromagnets cycle between being on and off. Each time it cycles on, it can give a push to a moving wheel just as the hammer keeps hitting the bell in the fire alarm. These repeating pushes can make a wheel spin and cause motion in home appliances such as an electric beater, toothbrush, blender, or model train.