electromagnetism - Electromagnetic fields vs electromagnetic radiation

As I understand, light is what is more generally called "electromagnetic radiation", right?
The energy radiated by a star, by an antenna, by a light bulb, by your cell phone, etc.. are all the same kind of energy: electromagnetic energy, i.e. photons traveling through space.

So far, so good? (if not please clarify)

On the other hand, there are these things called "electromagnetic fields", for example earth's magnetic field, or the magnetic field around magnets, the electric field around a charge or those fields that coils and capacitors produce.

Now here is my question:

• Are these two things (electromagnetic fields and electromagnetic radiation) two forms of the same thing? or they are two completely different phenomena?


• If they are different things, What does light (radiation) have to do with electromagtetism?

I'm not asking for a complex theoretical answer, just an intuitive explanation.

Answer

Electromagnetic radiation consists of waves of electric and magnetic fields, but not all configurations of electric and magnetic fields are described as "radiation." Certainly static fields, like the Earth's magnetic field and the other fields you describe, are not called "radiation."

There is a standard technical definition of electromagnetic radiation, but roughly speaking, we think of a configuration of electromagnetic fields as constituting radiation when it has "detached" from its source and propagates on its own through space. One of Maxwell's equations says, in effect, that a changing magnetic field produces an electric field. Another says that a changing electric field produces a magnetic field. An electromagnetic wave results from these two processes producing a steady flow of radiated energy that persists far from the source.