General Caption: Note the old IN/IS dichotomy or the single meaning for the two locutions:
- Electromagnetic radiation (EMR)
is a traveling,
self-propagating,
transverse wave state
IN the electromagnetic field
which is everywhere always in
all spacetime---as illustrated in the images.
This what is one says when being very exact.
- Electromagnetic radiation (EMR)
IS a traveling, self-propagating
electromagnetic field---where one
means by
electromagnetic field the particular
electromagnetic-field STATE
constituted by the particular set of
traveling,
self-propagating
EMR waves that
you are considering.
- The first locution is exactly true, but the second is what people usually say---it just easier to say: i.e., electromagnetic radiation (EMR) is a traveling, self-propagating electromagnetic field.
- The EMR is independent of source or sink.
- To generalize, one almost always says electromagnetic field meaning a particular electromagnetic field state. mutatis mutandis for electric field and magnetic field.
Illustrations of the electromagnetic field which is everywhere always.
- Image 1 Caption:
Diagram of
electric charge
(positive charge (+)
and negative charge (-))
arrangement in oddly shaped
electrical conductors
and the overall
electrostatic field
both caused by the fixed placement
of an ideal point charge
(a with positive charge (+)).
The electric field lines are a visualization tool that at every point align with the electrostatic field at that point: the arrows give the direction of the electrostatic field.
At the macrosopic level, there is NO electromagnetic field inside the electrical conductors, but at the microscopic scale there is---it just is small scale and averages away at the macroscopic scale.
Remember the electromagnetic field is everywhere always in all spacetime.
- Image 2 Caption:
"An alternating current (AC)
through the solenoid, producing a
changing magnetic field.
This magnetic field causes
an electric current
to flow in a wire loop by
electromagnetic induction"
(see Wikimedia Commons:
File:Electromagnetic induction - solenoid to loop - animation.gif:
slightly edited).
The magnetic field lines are a visualization tool that at every point align with the magnetic field at that point: the arrows give the direction of the magnetic field.
- Image 3 Caption: "An animation of a half-wave dipole antenna (a stardard radio antenna) emitting radio waves (radio band fiducial range 3 Hz -- 300 GHz = 0.3 THz, 0.1 cm -- 10**5 km
