I find your post baffling. You casually contradict yourself. Is
there a language issue here, perhaps? Est que c'est que, si vous
pouvez vous expliquer en français, vous seriez plus claire? I doubt
it -- your English is excellent, I don't think that's the problem.


On Tue, 24 Oct 2006 16:42:14 +0000, srp wrote:

sal a écrit :

On Sat, 21 Oct 2006 14:52:17 +0000, srp wrote:

FrediFizzx a écrit :

"srp" <srp2@globetrotter.net> wrote in message
news:453937D3.8020207@globetrotter.net...

Radium a crit :

Randy Poe wrote:

Neutrons also have a magnetic moment. Neutron stars have very
strong magnetic fields.

http://groups.google.com/group/sci.physics.research/browse_thread/thread/3e9165cf392ad391/35837736a0f3333c#35837736a0f3333c


Apparently neutrons are also "electric". The overall electric
chage of the neutron maybe neutral but it is still made up of
charged particles.

However, the person who posted the message in
http://groups.google.com/group/sci.physics.research/msg/029a72c00e1c69c9
claims -- at least in my interpretation -- that magnetism can exist
in the complete absence of any electricity. How is this possible?

It is not possible.

Note that "electric charge" is not the same as "electric field".

Straight from Maxwell, both electric and magnetic fields cannot exist
separately.

Straight from Maxwell, certainly they can. Here's a perfectly good
solution to the field equations:

E = (E_x, 0, 0)

B = (0, 0, 0)

Curl and divergence of E and B are both zero, nothing's varying with time,
and Maxwell is happy.

If you demand a physical source for the aforementioned E field use a
couple of charged plates. In Maxwell's world the electrons had no
magnetic moments and a pure E field was no problem, at _any_ scale.

In any volume of space, the density of electric field energy is
always equal to the density of magnetic field energy.

Hi André,

I think perhaps you might want to make extra qualifications about
this. ;-) Certainly, magnets have no electric field macroscopically.

Right on the money, as usual, Fred :-)

You're right, of course.

Whoops you just contradicted yourself, assuming we're all speaking the
same language here. That B field outside the magnet seems pretty
seriously free of an E field, which you just said can't happen. So what
on Earth do you actually mean?

The magnetic dipole moments are additive (do not cancel each other when
in parallel alignment.

In my model,

In **YOUR** model? Yet elsewhere in this thread you state "I claim
nothing original." If you claim nothing original, then how can this
be a discussion of **YOUR** model?

Please make up your mind.

the summed up elementary dipole moments making up the
macroscopic field of magnets are those of the carrying energy of
the electrons involved, not those of the electrons
themselves. Since the (unsigned) charge pairs of each microscopic
carrying photon amounts to neutral, they do not add up and remain
locally individual.

The so-called Bohr magneton mu_B for example, is not the dipole
moment of the electron, but that of the energy induced at the
ground state of the H atom. It is the dipole moment of the
electron carrying-photon at the H ground state.

So are you saying the energy density of the B field around the
magnet is actually zero, or are you claiming that in some way the
energy density of the (zero-strength) E field is somehow nonzero
and equal to the B field's energy density?

I said nothing of the sort. Just read back.

I beg your pardon, you certainly did.

First, please note: If there is a macroscopic B field around the
magnet, but no macroscopic E field, then the energy density of the B
field in any small unit of volume near to but outside the magnet must
be nonzero while the energy density of the E field in that same volume
must be zero.

*BUT* you said -- and you quoted it yourself, below --

"In any volume of space, the density of electric field energy is
always equal to the density of magnetic field energy."

The magnetic field energy density is proportional to the squared
intensity of the magnetic field. The electric field energy density is
proportional to the squared intensity of the magnetic field.

You said "in _any_ volume of space". I pick, for example, a small
volume of space just outside a permanent magnet. There is a magnetic
field in that particular volume of space, but there is no electric
field in that volume of space. The energy density of the magnetic
field in that volume is therefore nonzero, while the electric field
energy density in that volume is zero. They cannot be equal in that
case, yet you said they are "always equal". If that's not what you
meant, what _did_ you mean?

The balloon case given elsewhere provides a related but opposite
example, of course.

I simply quoted a basic foundation of electromagnetism that can be
found in any EM textbook.

Cite book, chapter and page where that quote came from.

I'd appreciate it if you'd post the entire paragraph you think
supports your point.

If you are not familiar with electromagnetism,

I certainly am and if the assertion you cite came from an E&M
textbook, then it was lifted out of context with consequent distortion
of its meaning.
Again, please cite book, chapter, and page, and if possible please
post the entire paragraph rather than the single sentence you have
quoted so far. It cannot mean what you are using it to mean.

I simply suggest you get hold of one and verify yourself.

"In any volume of space, the density of electric field energy is
always equal to the density of magnetic field energy."

Context please. The statement is false as it stands, so if it came
from a textbook, you lifted it from context which modified its
meaning.

I even gave you the equations that can be found in any detailed
textbook on electromagnetism.

You have apparently asserted that Maxwell's equations have only one
general form of solution, in which the E and B field energies are
equal.

That's wrong.

There are actually (at least) three distinct classes of solutions to
Maxwell's equations in free space:

(a) IF at some particular point there is, in _some_ inertial frame, an
electric field but _NO_ magnetic field, then there is, in _every_
inertial frame, a nonzero electric field at that point.

You cannot
transform away the electric field in that case. (This can be seen
just by observing the behavior of any point charge from the frame in
which there is just an E field.)

(b) IF at some particular point there is, in _some_ inertial frame, a
magnetic field but _NO_ electric field, then there is, in _every_
inertial frame, a nonzero magnetic field at that point. You can't
transform away the magnetic field in this case. (This is only
slightly harder to see than case (a), and in fact if we pretend we
can observe magnetic monopoles moving at various velocities, it's
immediately obvious.)

(c) IF at some particular point there are, in _some_ inertial frame,
magnetic _and_ electric fields, oriented perpendicular to each other,
and equal in magnitude

, then neither one can be transformed away.

This implies, among other things, that you can't transform away
electromagnetic radiation just by changing to a different inertial
frame. Combined with (a) and (b) it also implies that, if there is no
EM radiation at a point in _one_ inertial frame, there should be none
in _any_ inertial frame. (The class of solutions in which both E and
B fields are essential includes other cases as well but the exact test
for it slips my mind at the moment.)

You seem to be ignoring cases (a) and (b) completely.

If you think you're not, please explain how the E and B field energy
densities can be equal at a particular location in a frame of
reference in which there is an E field but no B field.

srp wrote:

sal a écrit :

On Sat, 21 Oct 2006 14:52:17 +0000, srp wrote:

FrediFizzx a écrit :

"srp" <srp2@globetrotter.net> wrote in message
news:453937D3.8020207@globetrotter.net...

Radium a crit :

Randy Poe wrote:

Neutrons also have a magnetic moment. Neutron stars have very strong
magnetic fields.

http://groups.google.com/group/sci.physics.research/browse_thread/thread/3e9165cf392ad391/35837736a0f3333c#35837736a0f3333c


Apparently neutrons are also "electric". The overall electric chage of
the neutron maybe neutral but it is still made up of charged
particles.

However, the person who posted the message in
http://groups.google.com/group/sci.physics.research/msg/029a72c00e1c69c9
claims -- at least in my interpretation -- that magnetism can exist in
the complete absence of any electricity. How is this possible?

It is not possible.

Note that "electric charge" is not the same as "electric field".

Straight from Maxwell, both electric and magnetic fields cannot exist
separately.

In any volume of space, the density of electric field energy is always
equal to the density of magnetic field energy.

Hi André,

I think perhaps you might want to make extra qualifications about this.
;-) Certainly, magnets have no electric field macroscopically.

Right on the money, as usual, Fred :-)

You're right, of course.

The magnetic dipole moments are additive (do not cancel each other when in
parallel alignment.

In my model, the summed up elementary dipole moments making up the
macroscopic field of magnets are those of the carrying energy of the
electrons involved, not those of the electrons themselves. Since the
(unsigned) charge pairs of each microscopic carrying photon amounts to
neutral, they do not add up and remain locally individual.

The so-called Bohr magneton mu_B for example, is not the dipole moment of
the electron, but that of the energy induced at the ground state of the H
atom. It is the dipole moment of the electron carrying-photon at the H
ground state.

So are you saying the energy density of the B field around the magnet is
actually zero, or are you claiming that in some way the energy density of
the (zero-strength) E field is somehow nonzero and equal to the B field's
energy density?

I said nothing of the sort. Just read back.

You originally claimed they were always equal, you may recall.

I don't really understand what your problem is. I claim nothing
original.

I simply quoted a basic foundation of electromagnetism that
can be found in any EM textbook.

You claim various results which are true for propagating
EM waves. What you write is true for EM waves. What you
keep missing is that EM waves are not the only solutions
for the Maxwell's equations, i.e., not the only form in which
electric or magnetic fields appear.

If you are not familiar with electromagnetism, I simply suggest
you get hold of one and verify yourself.

Everything you've said is true for the special case of
propagating EM waves, but not true in general.

"In any volume of space, the density of electric field energy is
always equal to the density of magnetic field energy."

Yes, that is a true statement for the special case of the
propagating EM-wave solution, but not true in general.