Faraday paradox revisited,magnetic field rotation question.

[guest1289]

1: When the magnet spins with the disk, the disk serves only as a conductor and current is generated from the flux cutting the brush/external conductor.

    - When the aluminium-disk has current flowing through it,  surely it must produce an electromagnetic-field (  I assume that  that  electromagnetic-field    is so small that it is disregarded in this experiment ) .
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     The  Earth's-Magnetic-Field
      -  Does this experiment need to be done up in space somewhere, to totally exclude any interference  'in any way' from the earth's-magnetic-field(  and Earth's-Electric-Field  etc ) .
          I say this because this experiment is :
            -  done at a very high rpm
            - the earths field is strong enough to enable a compass to function

          Spinning the Aluminium-Disk Without the Magnetic-Disk anywhere near it.
           -  So, if you just spin the  aluminium-disk  without the Magnetic-Disk anywhere near it,  horizontally( or is that vertically ) in relation to earths surface,   THEN,  shouldn't it generate some current from it's interaction with the earth's-magnetic-field(  or Earth's-Electric-Field  etc ),  but I assume the current generated would be very small .   
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    Those  Magnokraft designs ( ufo propulsion, I assume using a  magnetic-field-repelling  against the earths-magnetic-field ),  for those designs it wouldn't matter if the magnetic-field spins with the magnet or not,  since they would just worry about the magnetic-field intensity / size .
     The last thing I read about those,  was that  they wanted to try  using  superconductors( or,  superconducting  neodymium ), I can't remember .

   So now I assume that the  fast-rotating-magnets  in the hoverboards,  are not  single  One-Piece  Disk-Permanent-magnets,  instead they would be fast rotating wheels with a couple of magnets set into the wheel,  to state  the  obvious.
     

[Low-Q]

I just ordered some magnets for final experiment.

meanwhile..

this probably has been discussed 100 of times but once again for sake of this topic:
Would a magnet like this rotate if current flows in wire ?
What will happen if compass is inside the ring?

The magnet will not rotate.
The compass will not point in any fixed direction.


Vidar

[kmarinas86]

I just ordered some magnets for final experiment.

meanwhile..

this probably has been discussed 100 of times but once again for sake of this topic:
Would a magnet like this rotate if current flows in wire ?

It would not rotate. What you have to consider is that magnets carry embedded magnetization currents, and these give rise to an equivalent surface current. If you have a compass needle, that equivalent surface current will run across the magnetic field on the sides of the compass needle facing toward or away from the magnetic field. So if you have a compass needle in that magnetic field, there will be a torque on compass aligning it with the circular magnetic field of the current based on q(v x B). the However, the magnet you have here is a ring magnet that is magnetized radially. The equivalent surface current in this case runs along the circumference along concentric rings centered on the axis of the ring magnet. The result is that the equivalent surface current on the ring magnets that will run parallel to the magnetic field lines of the wire current, so there will be no Lorentz force q(v x B) and the magnet will fail to turn.

What will happen if compass is inside the ring?

It will align with the combined magnetic field of the permanent magnet and the current through the wire. If you put it in the exact center, then it will have no preferred direction of alignment.

[kmarinas86]

Would have to be individual mags to make the ring, if it did work.

There would be a torque on the individual magnets, but torque on the individual magnets does not automatically mean torque on an arrangement of magnets on a disk. Note that the torque on the individual magnets would cause opposite forces on opposite ends of each magnet, which is why a compass needle turns in the presence of the magnetic field of a wire current. However, if you are taking about rotating the rigid ring magnet assembly with the magnets oriented perpendicular to the wire path, those same forces which apply a net torque on the individual magnets do not apply a net torque to the whole assembly because those forces are directed toward/away from the wire. The reason? You have to consider that the force on the magnet is actually the force on the equivalent surface currents that are the sum of all magnetization currents within that magnet. The forces that turn the magnet are at right angles to both the wire current's magnetic field and the equivalent surface current of that magnet, which wraps around the surface between the magnet's poles. If your poles are oriented at right angles to the wire, then the equivalent surface currents running along the side perimeter of each magnet will cross the magnetic fields of the wire current and will result in Lorentz forces that are perpendicular to the wire, which means the rigid magnet assembly will not revolve around the wire, although their will be a stress on each magnet attempting (in vain) to rotate the magnets at their the current position.

[guest1289]

       The only  replicated-test  that makes me wonder about the  correctness  of the  Faraday-Paradox,   is,  The first ever  electric-motor,  which was invented by  Faraday.
       ( the paradox  implies that the field of a  disk-permanent-magnet  stays stationary when the disk-magnet  rotates )

   This motor came in two configurations :
     ( 1 ) -   the  current-carrying-wire,   rotating  around  the  permanent-cylinder-magnet
     ( 2 ) -   or,  the  permanent-cylinder-magnet  rotating  around  the  current-carrying-wire

       The two configurations can be seen in the diagram in the link below :   

       https://en.wikipedia.org/wiki/File:Faraday_magnetic_rotation.jpg

       Every description I have read about this motor states that the rotation is  simply  as a result of the interaction between the field of the   current-carrying-wire,   and   the field of the  permanent-cylinder-magnet.

       And yet the  Faraday-Paradox, and the statements from most members on this site,  imply  that  that   permanent-cylinder-magnet    'Should Not Rotate',  and yet it  does.

      (  Admittedly,  I can't determine if or not  electric-current  flows through the  permanent-cylinder-magnet  in this  motor,  if it does,  then why didn't he just replace the  permanent-cylinder-magnet  with  another   current-carrying-wire or conductor .
        So,  A DEFINITIVE TEST would be if someone would make a version of this motor that would  ensure  that no  electric-current  flows through the  permanent-cylinder-magnet,   so instead of using the liquid( mercury, or brine ) in this motor,  it could use  brush-contacts instead     )

     NOTE : The versions of the homopolar-motor like the version in the link below,  would not be suitable for  A DEFINITIVE TEST
        https://en.wikipedia.org/wiki/File:Homopolar_Motor_Large_neutral.jpg