4 "Roy Lewallen" wrote
...
K7ITM wrote:

For what it's worth...

I've often found it useful to consider alternate ways to think about
things. In this thread, there have been some comments about electric
fields, magnetic fields and electromagnetic fields. So, I ask: how
do we measure fields? As far as I know, it's by their interaction
with matter: we observe how an electromagnetic field accelerates
electrons, for example. Do we have any way other than by observing
how a (E, M, or EM) field interacts with matter to measure a field?
If not, does a field _necessarily_ have any physical reality, any
reality beyond a mathematical model to explain what we observe?
. . .

On the first day of the first class of Electromagnetic Fields, I asked the
professor (Carl T.A. Johnk, author of _Engineering Electromagnetic Fields
and Waves_), "What is an electromagnetic field?" His answer: "It's a
mathematical model we use to help us understand phenomena we can observe
and measure." And I see that in the second paragraph of his book he writes
"A field is taken to mean a mathematical function of space and time." I've
been satisfied with that definition.

Wiki wrote: "The field can be viewed as the combination of an electric field
and a magnetic field. The electric field is produced by stationary charges,
and the magnetic field by moving charges (currents); "

But what produce very slow charge?

Next Wiki weote: "From a classical perspective, the electromagnetic field
can be regarded as a smooth, continuous field, propagated in a wavelike
manner ;"

It is important to know that Maxwell's waves are rotational (oscillating
magnetic whirl).

Alternate electric field also propagate in a wavelike manner. But here to
and fro (no rotations).

The fundamental question: Are radio waves a simple electric waves or the
very sophisticated Maxwell's waves?
S*