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).

On Wed, 9 Jul 2008 22:17:55 -0700 (PDT) Benj <bjacoby at (no spam) iwaynet.net> wrote:
| On Jul 9, 1:34 pm, phil-news-nos... at (no spam) ipal.net 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".

On Fri, 11 Jul 2008 02:15:29 GMT Don Kelly <dhky at (no spam) shaw.ca> wrote:

| 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?

My understanding is that "paradox" is simply the paradox Faraday thought
of
this back in his day when he did this experiment. He thought it a paradox
since it didn't follow his theory of induction. Now we know it followed
the
Lorentz theory, instead, which came later than Faraday. So it is no
paradox
to us, anymore. But the term "Faraday's paradox" is still a reference to
the
concept Faraday was exploring.


| One can analyse a homopolar machine using Faraday and can also do it
using
| Lorentz -the latter may be somewhat more elegant .

As I understand this, there are two ways to induce a voltage potential and
a
current in a conductor in a magnetic field. One is for the field flux
itself
to change its vector intensity relative to the conductor. That would be a
mere density change in a transformer, for example. If the field lines are
rotating (this is not the same angle of rotation of the Faraday disk) such
that the lines change from crossing the conductor to going parallel to it,
there would also be an induction taking place in cycles according to that
rotation. The other way to induct a voltage potential is for the
conductor
to move at a right angle to the field and to its direction of conduction.
Then you get a voltage/current with a polarity specified by Fleming's
right
hand rule. This is what the disk is doing.


| In the case of moving vs stationary magnets- consider the whole path and
the
| flux enclosed- otherwise ???.

Of course the "extraneous field" needs to be considered. If the magnets
are
covering just a portion of the disk near the axis, even though a full 360
degrees around the disk, there is not only the field line between the
magnets
going through the disk, there is also a field raidally beyond the magnets,
giving a field shape somewhat resembling a torus. Part of the disk will
rotate in the inner field and part will rotate in the outer field, and
there
will be induced potential that mostly cancels out.

My idea is to design the field shape to eliminate the extraneous field by
having alternating sets of magnets with reversed poles. At even radial
angles, NORTH faces the disk from above and SOUTH from below, while at odd
radial angles, NORTH faces the disk from below and SOUTH from above. Now
this arrangment mostly removes the extraneous field. However, it will end
up with "shorted out" circulating currents in the disk.

The fact that the magnets can be rotated with the disk in sync and this
will
still induce the electrical charge allows modifying the disk to take
advantage
of the alternations of polarity between even and odd angles by cutting out
the
disk until what remains is a conductor that zigs under the field of the
even
angles and zags under the opposite field of the odd angles. This would
still
be a conductor in a loop and still be "shorted out". At this point just
break
the loop by cutting the conductor somewhere and insert a device to measure
or
indicate the voltage/current present (a light, for example).

By even and odd angles, I'm visualizing 12 angles of the common clock.
But
any even number of angles can used as desired.

With my currently limited ability to fabricate these things, I'm going to
do
these thought experiments first to find what things I should not waste my
time
on, and what things I might consider seriously building.


| 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.

I will look into this. But I get the impression it may not be what I am
thinking about. In particular, I want to work with whatever involves the
conductor AND the magnetic field moving together, as in the original
paradox
that Faraday observed, but extended in some way.


| 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).

Yes, that kind of rotation can exist. If I place a strong magnet at one
edge
of a disk with N-pole facing the axis, and another at the 180 degree edge
with
S-pole facing the axis, there will be field lines (B) cutting through the
axis
and when the disk rotates, these lines rotate. If I place a conductor
(nearly)
crossing the axis, parallel to the disk, but close enough to be in this
field,
then the rotation of the disk will result in the lines alternating between
being in parallel to that wire and perpendicular to it. I would expect
this
to induce a potential in that wire by Faraday's law of induction, not but
the
Lorentz force.

By my interest is not in that direction. My interest is in finding ways
to
extend the concept of the Faraday disk with the magnets attached to the
disk,
including better confinement of the extraneous fields. Consider my design
involving the zigs at even angles and zags at odd angles (through the
whole
of the disk, not different on each side as your suggest similar to the
Gramme
ring motor). If that idea works (and logically it seems to be the same
thing
as the original "Faraday homopolar generator with magnets rotating with
the
disk"), then the next extension is to replace the disk with 6 zigs and 6
zags
with a non-conductive non-ferrous disk (wood? plastic?) with one that is a
form that allows winding a lot of copper wire suitable for winding coils,
but
in that same 6 zig and 6 zag pattern (where in reality a larger disk would
replace 6 with a larger number). Then there would be effective a very
LONG
conductor moving within a magnetic field where nearly all portions of the
wire
would be under the very same polarity of influence according to Fleming's
right
hand rule and the Lorentz force law. So the question then is does this
make an
even higher voltage than a plain disk, at the end points of this LONG
wire?

FYI, I could make the end points both be at the axis, and conduct a
conductive
axis that is insulated in the middle at the non-conductive disk form, and
then
use that to attach the wires and brushes to extract the electric current.

But will it really work? If not, where does the theory break down and
why?
-------------------------------

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