When we think “magnet,” we might envision those things we stick on our fridge door. It may be a bit confusing, then, to discover that magnetism is closely related to electricity. In fact, there is a single force—the electromagnetic force—that governs the behavior of both magnets and electric charges.

We have seen that there is a reciprocal relationship between electric charges and electric fields: electric charges generate electric fields and electric fields exert a force on electric charges. Similarly, there is a reciprocal relationship between a moving electric charge and a magnetic field: a moving electric charge creates a magnetic field, and magnetic fields exert a force on moving charges.

Bearing this reciprocal relationship in mind, we can make sense of electromagnets, the on-off magnets you see, for instance, lifting and dropping cars at the junkyard. The magnetism in these electromagnets is generated by a current running through the magnet that can be turned on and off at will. However, we still haven’t explained how any of this connects with the permanent magnets we stick to our fridge door.