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2019-04-22, 07:13:42
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Author Topic: PERMEABILTY and PERMITTIVITY  (Read 23371 times)

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Posts: 3044
tExB=qr
Can I throw my penny-worth into the debate about the Faraday disc homopolar generator.  When you consider the field from the magnet actually comes from a large number of aligned electron spins, and if we model those electrons as electric charge that is really spinning, should we not consider the spin rate of those electrons when we think of the magnet rotating?  A small spherical volume charge or surface charge models an electron, and the translatory speed within the electron volume or on the electron surface is what we should consider when dealing with relative velocity between source and observer.  IOW what we observe as a magnetic field (by noting its effect on conduction electrons in our experiments) is really an effect due to the relative motion between our test electron and those electron surface or volume charge movements.  IMO at practical spin rates for the magnet it is nonsense to think that the field is rotating because that relative motion doesn't change.  Only if we could spin the magnet at something approaching the spin of the electron would we observe anything!!

We could, if we put our mind to it, create a pseudo magnet by having an array of charged spheres each one spinning, each driven by a tiny electric motor.  Or just perform a gedanken experiment in our minds.  Of course this array would need to include the same number of non-spinning spheres of opposite charge so as to make it electrically neutral and eliminate any external E field. Now use this magnet in the homopolar experiments.  It would become quite clear that rotating the bulk object at spin rates that are small compared to that of the charged spheres doesn't affect the field.  A Faraday disc rotated within the field, whether or not the "magnet" rotates with it, would obtain homopolar induction.  The thing that creates the induction is the relative motion of those charged sphere surfaces as seen by the conduction electrons in the disc.  Our concept of magnetic field is just a means of conveying that induction effect.  Boil our pseudo magnet down to a single spinning charged sphere and it becomes even more obvious that rotation of the "magnet" is a nonsense idea, it is already spinning like mad inside.

Smudge

Faraday's Law doesn't consider the magnet to be a rotating charged sphere, or spheres.  You could look at it another way: the magnetic field of a circular magnet rotating about its center is homogenous.  Therefore, the magnetic field is not varying in magnitude or direction relative to the conductor, so no current is induced.  This doesn't tell us much about induction though.

I think the GFT Theory adds a lot more to the picture since it considers the charges in the conductor, and why a current is induced at all.  In the document above, tech29d.pdf, the author also applies the theory to capacitors and motors.
   
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Faraday's Law doesn't consider the magnet to be a rotating charged sphere, or spheres.  You could look at it another way: the magnetic field of a circular magnet rotating about its center is homogenous.  Therefore, the magnetic field is not varying in magnitude or direction relative to the conductor, so no current is induced.  This doesn't tell us much about induction though.

I think the GFT Theory adds a lot more to the picture since it considers the charges in the conductor, and why a current is induced at all.  In the document above, tech29d.pdf, the author also applies the theory to capacitors and motors.

Yes an interesting theory.  There is another form of homopolar generator that is a conducting cylinder placed over one end of a cylindrical magnet so that the flux lines that spread out pass through the cylinder wall.  When the cylinder is rotated there is an induced emf along the cylinder.  Don't know whether the GFT theory applies there.  It has the same novel feature that it doesn't matter whether the magnet rotates with the cylinder or not.

I like to think that every magnetic field is due to some charge somewhere that is moving, and the real theory for magnetic effects involves relative motion between those charges and the test charge.  Faraday's law of induction is really a simplification of the more complex situation.  But each to their own as they say.

Smudge
   

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Posts: 3044
tExB=qr
Yes an interesting theory.  There is another form of homopolar generator that is a conducting cylinder placed over one end of a cylindrical magnet so that the flux lines that spread out pass through the cylinder wall.  When the cylinder is rotated there is an induced emf along the cylinder.  Don't know whether the GFT theory applies there.  It has the same novel feature that it doesn't matter whether the magnet rotates with the cylinder or not.

I like to think that every magnetic field is due to some charge somewhere that is moving, and the real theory for magnetic effects involves relative motion between those charges and the test charge.  Faraday's law of induction is really a simplification of the more complex situation.  But each to their own as they say.

Smudge

GFT applies to the cylindrical version of the homopolar generator/motor as well, as it is just the disc version rotated.  I expect GFT to also explain the Roentgen Current, Wilson-Wilson Effect, and the Rowland Effect more clearly than current explanations.  More importantly, I believe GFT will also disclose other methods of inducing a current utilizing the inherent spin of particles.
   
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