On 09/11/14 13:01, Sn!pe wrote:
gareth wrote:

"Sn!pe" wrote in message
.uk...
gareth wrote:

"Sn!pe" wrote in message
o.uk...

What produces the electric component of the EM field?


The changing magnetic field.

Of course, it should go withour saying that the axis of spin must
be between the N and S poles, and not along the axis of the magnet,
in case of confusion thereto.


I don't understand. Is it not the case that the electric component of
the EM field arises from a voltage difference? How does that voltage
difference arise, please?


I suggest that you go back to an earlier level and think about the dynamo,
alternator and transformer, where a changing magnetic field produces
an electric field, for it is the same principle.


Do not dynamos, alternators and transformers rely on currents induced
into *conductors* by changing magnetic fields? Please see 'Faraday's
Law of Induction' regarding the current induced into a conductor.

https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

Where is the conductor in your 'rotating magnet' suggestion? Is it not
the case that the current gives rise to the potential difference from
which the eletric field arises? It is the current that is directly
responsible for the magnetic component, of course.


It is unfortunate that matters of electricity are very difficult to
understand
in full, so we are presented with a series of models (usually starting off
with the increasing pressure as the depth of water in a bucket is increased)
none of which are absolutely correct, but all of which get us over a hurdle
of understanding until along comes the next model.

And the biggest partial model that leads to much understanding is that
electricity is all about pos and neg charges whereas in fact it is
all about the EM fields!


I agree that "It is unfortunate that matters of electricity are very
difficult to understand in full".

Perhaps I'm just being dense, but I still don't see how the electric
component of the propagating EM field arises in your scenario. I have
to admit, though, that it's probably 50 years since I last looked at
this stuff in (I think) the ARRL Handbook, perhaps my memory is at
fault.



You are not 'being dense', you are perfectly correct.

Waving a magnet will not generate an EM wave, it won't even induce a
current unless there is a conductor to hand.

Likewise, waving a battery around, won't generate an EM wave either.

Maxwell's equations come as a 'set' to generate an EM wave, you can't
start with just one. That was one of the flaws in the Cross Field
Antenna theory-or the original one, it varied as it was challenged. It
had other flaws, eg the idea that the Poynting vector was some 'extra'
physical phenomenon which could be 'synthesised', rather than just a
mathematical vector representation of the power in the E and M fields.

As I pointed out in a previous post, the differential term is zero in
the absence of one of the fields so the equations have no, non-trivial,
solutions.

As I recall, this is one of the standard things you are taught when you
attend a lecture on Maxwell's Equations. Perhaps someone missed a
lecture (or more),has lost some crucial pages from his notes,or hasn't
got a clue.

Like all equations, if you apply them correctly, Maxwell's equations do
work. However, if you can't understand them, you will mislead yourself.