Re: Faraday paradox in non-circular form

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<phil-news-nospam@xxxxxxxx> wrote in message
news:g558vk0bg8@xxxxxxxxxxxxxxxxxxxx
On Wed, 9 Jul 2008 22:17:55 -0700 (PDT) Benj <bjacoby@xxxxxxxxxxx> wrote:
| On Jul 9, 1:34 pm, phil-news-nos...@xxxxxxxx wrote:
|
|> My understanding of the homopolar generator is that the entire disk
would be
|> under the influence of a uniform magnetic field that, from the point of
any
|> particle of the rotating disk, is not changing in intensity (so as to
not be
|> influenced by Faraday's law of induction which would apply when the
field is
|> changing). The paradox is that when the disk is rotating, it does not
matter
|> if the magnet(s) creating the field are rotating with the disk or not
(or in
|> any other way including in the opposite direction).
|
| This is correct. The "paradox" comes from the question of whether the
| magnetic field rotates with the magnets or not. BOTH assumptions give
| the SAME answer! If the magnets are fixed and the disk rotates,
| Lorentz forces induce an emf in the moving disk. However, if the
| magnets are attached to the disk and spun, now there is no relative
| motion between the magnetic field and disk so no induction can occur
| there. BUT, if the magnetic field is assumed to rotate with the
| magnets, then that would produce an emf in the REST OF THE WIRES GOING
| TO THE METER, that can be shown identical to the EMF in the first case
| of the rotating disk with fixed magnets. No solution to this paradox
| seems possible using wire loops.

Is it really a paradox to be solved now? Isn't the understanding of the
Lorentz force the solution? I think the point is that a magnetic field
isn't changed in any way by the magnets being turned (as long as the
shape of the field remains the same ... turning a magnet that is not
circular would turn the shape of the field, complicating things) and so
there is no change in the field where the wires are if the magnets are
rotated. And thus, attaching the magnets directly to the disk which lets
them rotate with the disk, still imparts the same field on the disk.


| The proposed research is to measure the induced Lorentz field of a
| spinning magnet using electrostatic methods. That gets around the
| "loop" induction problems. As far as I know nobody has done this that
| we've heard about.

In the classic case of a solid disk, with a disk shaped magnet on each
side
of the disk, one with N-pole facing the disk, and the other with S-pole
facing the disk, there would be a "return field" outward and around the
whole disk/magnet assembly. Since the wires attached to the brushes that
connect to the rotating disk are not moving, they should not have any
electrical charge applied.

But I have another idea.

Consider a construction of a disk to be rotated that is done this way.

A wire runs outward from near the axis to the edge, with magnets fastened
on each side so it has a specific magnetic field direction. Now run that
wire a short radius along the edge of the disk, then back inward toward
the axis. The 2nd part of the wire would have the magnets flipped so the
magnetic field is reversed, so the 2nd part of the wire gets a charge in
the opposite direction. It does not go all the way to the axis. Then it
wraps back for a 3rd stretch towards the edge again, this time with the
same field orientation as the 1st run. Repeat this a few times around the
disk (which is otherwise non-conductive), until the wire comes back to the
starting point. Where it meets back up to its other end, attach some kind
of DC power sensing device, such as an LED light.

So we have a non-conductive disk base, a wire "zig-zagging" between near
the axis ("near" does not have to be real close, just some distance from
the edge) and the edge, going around the disk with N zigs and zags, with
the field fixed over the wire so it has one orientation on the "zigs" and
the other orientation on the "zags".

-----
It appears that everyone is looking for a paradox where one may not actually
exist. Step forward from the Faraday disk to Maxwell's equations. Is there
a changing total field in any part of the region enclosed by the path? How
about another path?
One can analyse a homopolar machine using Faraday and can also do it using
Lorentz -the latter may be somewhat more elegant .
In the case of moving vs stationary magnets- consider the whole path and the
flux enclosed- otherwise ???.

Yes a homopolar motor will work. it will, like the homopolar generator, be
of very limited use. A better design of such a motor exists- it is a
printed circuit motor which has a conventional DC winding (zigs on one side
ans zags on the other) and brushes. The brushes can be at the axle or at the
perimeter- Light, not necessarily high current, low voltage- simply a
conventional motor squeezed (axially) flat. The zigs and zags that you
indicate are a precursor of this- the Gramme ring motor flattened.

As fr existence of a rotating magnetic field- such do exist but the axis of
rotation is perpendicular to the field. Look at any induction or synchronous
machine (any of which is superior to a homopolar machine).
--

Don Kelly dhky@xxxxxxxxxxxx
remove the X to answer




.

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