Re: rotating magnetic field

On Apr 14, 4:01 am, pmb <pm...@xxxxxxxxxxx> wrote:

That is incorrect. There are forces acting on the charges inside a
conductor placed in the vicinity of the rotating magnet. However the
force is not a magnetic force, it’s an electric force. The magnetic
force is zero. The expression for the Lorentz force on a particle is
often misinterpreted. The v in qvxB is velocity of the charge, not the
velocity of the field (since that has no meaning). A charged particle
at rest near the rotating magnet *does* experience a force, but that
force is an electric force, not a magnetic force. A proper
understanding of this requires a discussion of relativity

v is the velocity of the charge WITH RESPECT TO the field. If
"velocity of the field" has no meaning then that implies that there is
some absolute reference frame to which all charge movement is
referred. I think MM killed that idea. As I said before. You can move
the coil or the magnet and still get an emf. It is the relative motion
between the charge and the field (which more or less moves with a
magnet) that is the "v" producing the "force" which is interpreted as
an "E" which moves a charge which becomes a current. How can it be
anything else?

As for the "electromagnetic" story now so popular among relativists
that somehow there is only one force that transforms magnetic fields
into Electric fields, I'm sorry, I just don't buy it. This is
equivalent to me showing how I can suspend a sheet of dielectric
against gravity using an electric field and then proclaiming that see?
Gravity and an electric field are really the same thing. You can
claim that magnetic fields don't exist and I'll buy that. They are
just a mathematical construct anyway without reality. But to claim
that magnetic effects all disappear throughout the universe just
because I have some relative motion doesn't make sense.

The electric force on the charged particle is due to the electric
field generated by the rotating magnet. The source of the electric
field is is from charges which appear on the rotating magnetic due to
the motion of the magnet. This too is a relativistic effect. The total
charge remains zero. The charges merely redistribute themselves.

No. It isn’t.

So you maintain that if I move a magnet the so-called "magnetic field"
it produces does NOT move with it. You say that the magnetic field
just hangs there in space and the qvxB forces that seem to be produced
by it are REALLY produced by ELECTRIC fields produced as a result of
that motion? I hope you've noticed that the divergence of magnetic
fields is zero while this is not true for electrostatic fields.


If you know of such experiments with results one way or the
other please provide the cites for us.

Experiment. No. Relativistic electrodynamics is the correct
explanation and the physics is well understood.

Hmm. So you are substituting theory for experiment as "proof".
This is not how I understand physics works.

Its hard to find it
but if you do a careful search of the literature you can find this
explained. Purcell has a treatment of relativistic effects of
electromagnet phenomena. The charge distribution due to rotation and
the electric field it generates is not that hard to calculate and is
found in the following text

“Classical Electromagnetic Theory,” Jack Vanderlinde, Wiley press
(1993). See page 316 problem 11-8 where the author has you calculate
the electric field appearing around a uniformly magnetized rotating
sphere. I worked out a similar problem in a web page I created to
explain the physics of a rotating magnet. See

http://www.geocities.com/physics_world/em/rotating_magnet.htm

Yes, I DO need to look into this more. I have been meaning to for a
long time as the popularity of the Magnetic field = electric field
ideas have grown in popularity. I am particularly interested in what
happens to two charged particles as they move along parallel to each
other even up to relativistic speeds. The story is that since there is
no relative motion they produce no magnetic fields against each other
even though in a lab frame they are currents. Hence an e beam only
sees electrostatic repulsion even near c. I do think there are things
to think about in this context. But oddly enough a changing magnetic
field actually can accelerate a particle to near c velocities.
(betatron)

.

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