Why study electromagnetism?

Electrical transformer Transformers turn high voltage into low voltage or low voltage into high voltage. They are an indepensible part of how we move electrical energy around. They rely on the twin facts that currents cause magnetic fields, and that changing magnetic fields cause voltages. This way, a changing current in one circuit can create voltages in another, moving energy from one circuit to the other.
Here are photographs of two devices that make use of an electromagnet.

door bell door chime
electric bell door chime
In the case of the bell, the electromagnet is easy to see! It is harder to see how this makes it ring. Here is the circuit for the bell. showing how the current flows in the doorbell The red wire goes from the battery to the electromagnet, and the yellow wire goes from the electromagnet to a post. When the clapper is back from the bell, it touches the post, and the blue part of the clapper is part of the circuit. When current is flowing, the electromagnet pulls on the clapper. As the clapper moves away from the post, the circuit is broken. But the clapper is already moving and goes over and hits the bell before its springiness returns it to its initial position. And then the cycle starts over!

The electromagnet for the door chime is just barely visible. When the door chime button is pushed, the electromagnet turns on and sucks the little iron rod inside itself. When the button is released, the spring throws the iron rod against the chime, giving a melodious "bong."
The section on electromagnetism