A short 160M antenna
 

"Brian Reay" wrote in message
...
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.

You bandy about that some do not understand Maxwell's Equations*****, but it
is
only you who does not seem to, for in the case of a static magnetic
field due to a current, the non-zero differential given by Maxwell's
Equations in a vacuum is (off the top of my head, EOE) ..

del cross B = Mu0* J

B being the Magnetic Field, Mu0 the permeability of free space
and J the current density.

Brian, M3OSN, Old Chum, why not give up whilst you are still
(a long way) behind?


***** Every day, almost every hour, it seems that you originate
personal insults.

Why do you behave like that?

A short 160M antenna
 

Jeff wrote in :

E cross H in mathematical terms.


'Cross product' of E and H? As in, related to 'dot product'? If so that might
be my wau in to understanding Maxwell, I've used dot product before,
translated myself to find intersections of lines, and saw cross product
closely related, documented pretty much beside it a couple of times.

A short 160M antenna
 

Jeff wrote:
On 08/11/2014 17:46, gareth wrote:
"Brian Reay" wrote in message
...

He isn't the first fool to think he could generate an EM wave breaking
Maxwell's laws.

You continue to be the one who originates ths abuse that you seek to lay at
others'
door, and you continue to misunderstand Maxwell.

The changing magnetic field cause by rotating a magent at such a speed that
it would cease to be a short antennae will create a changing electric field,
as described by Maxwell


For once have to agree with Gareth, a rotating magnet will cause EM
radiation.

Jeff

Nope, a rotating magnet will produce a rotatating magnetic field.

A moving magenetic field is a moving magnetic field and nothing more
than that.



--
Jim Pennino

A short 160M antenna
 

Jeff wrote:

Ok, maybe so. Is this right...? Suppose a wire is part of a closed circuit,
that magnet would certainly induce current. Now, if that wire were NOT
closed, but in the form of some antenna, then at an appropriate frequency, in
the part of an antenna that normally sees current (at the feedpoint end), you
would see a current, thus all the other attributes of an antenna subject to
an electromagnetic field would also exist? IF (I'm not stating, just trying
to follow a thought based on what you said), IF this is so, then it would
mean the EM wave existed with or without the wire, purely because the magnet
was spinning.

Alternatively, does it just mean that an alternative magnetic field near an
antenna feedpoint is as capable of inducing a signal out of the antenna as an
electromagnetic wave is?

Maybe I should go back to my popcorn. I may not even understand what I see,
but I want to watch.


It means that a rotating magnet will produce a radiated EM field,
nothing to do with any other piece of wire or antenna in close proximity.

Nope.


As Garth claims it is inherent in Maxwell's equations that this must happen.

Nope.

What Maxwell's Equations say is a moving magnet produces a moving magnetic
field.

A moving magnetic field is not an electromagnetic field.

If you want pictures then have a look at:
http://www.falstad.com/emwave2/index.html
and select rotating magnet and Poynting Vector.

Jeff

--
Jim Pennino

A short 160M antenna
 

Sn!pe wrote:
Sn!pe wrote:

Jeff wrote:

[...]

Run the java applet and in set up (top right) select rotating magnet,
and then select Show Poynting vector (or any other filed that you wish
to view)

Jeff.

Thanks, Jeff.

It seems that I lack a suitable Java installation, I'll look into it.

[later: now done]

OK, I've fixed that. I think it's probably time I did a bit of research
for myself, I've never heard of Poynting vectors and for the moment
I don't understand what I'm seeing. Anyway, thanks again, Jeff.

Yes, that is correct, you do not understand what you are seeing.


--
Jim Pennino

A short 160M antenna
 

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

What produces the electric component of the EM field?

The changing magnetic field.

Wrong.

There is no electric component therefore no electromagnetic field.


--
Jim Pennino

A short 160M antenna
 

wrote in message
...
Nope, a rotating magnet will produce a rotatating magnetic field.
A moving magenetic field is a moving magnetic field and nothing more
than that.

That is so wrong that I will leave it to others, others who perhaps have
sided with the redneck previously, to point out his error, and the use of
rotating
magnets to create electric fields in dynamos and alternators.

A short 160M antenna
 

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.

That is not a spinning magnet, that is a changing magnetic field across
a conductor which induces a current in the conductor which produces an
AC voltage in the conductor, or in other words, a generator.

No electormagetic field until you connect the wire with AC voltage
to an antenna which converts the AC voltage to an electromagnetic
wave.


It is unfortunate that matters of electricity are very difficult to
understand

Especially by babbling gas bags.


--
Jim Pennino

A short 160M antenna
 

Brian Reay wrote:

snip

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.

Precisely so; unfortunately most people do not have the math skills
to show that Maxwell's Equations say spinning magnets do not produce
electromagnetic fields.


--
Jim Pennino

A short 160M antenna
 

Jeff wrote:


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.

Thank you, Brian, I was beginning to doubt myself there. Not having
had the benefit of a University education like Gareth I tend to take
an empirical approach to this sort of thing.


Unfortunately this time Brian is not correct and a rotating magnet will
indeed produce an EM wave. The point that you have missed Brian is that
the differential term is zero for a static magnetic field, but when the
magnetic field is rotating analysis of the equations reveal that there
must be an E field produced in order to satisfy the full set of equations.

Have a look at the link in my previous post.

Jeff

Even if true, the presence of an E field and an H field alone is NOT
the same thing as an electromagnetic field.


--
Jim Pennino