Electromagnetism is a stunningly powerful idea. In fact. our lives would be unrecognizable without it. It is all about what happens when you combine electric charges, movement, and magnetic fields. Move a metal wire within a magnetic field, and you will cause an electric current to flow in the wire. This is how we generate electricity. Conversely, send an electric current through a wire, and the movement of electric charges will create a magnetic field. This is how we make the electromagnets that power most doorbells and particle accelerators. The third option is to run an electric current through a wire sitting in a magnetic field. The wire will move. This is the idea behind the electric motor in your kitchen whisk and power drill.The main credit for the theory rests with a Scotsman, James Clerk Maxwell, who first wrote down the equations that describe the complex interplay of electric and magnetic fields. The equations, it turned out. required an unexpected factor: the speed of light. This revelation led to the understanding that light and radiant heat can be thought of as moving variations in electromagnetic fields. These moving fields came to be known collectively as radiation.
Investigations of radiation led Max Planck to invent quantum theory and Albert Einstein to come up with his concept of relativity.by Michael Brooks, 30 Second Theory