Re: Error in Wikipedia article: Faraday's law of induction

On Sat, 12 Jul 2008 15:03:02 -0700 (PDT) Benj <bjacoby@xxxxxxxxxxx> wrote:

| I'll say this much. I'm also very much interested in this subject and
| would like to try to find a way to combine Lorentz and Faraday laws
| into one thing. I DO believe that as you put a current down a wire the
| magnetic field expands aways from a wire causing an apparent Lorentz
| force at a distance. After all, we know that as we put current down a
| wire energy is stored in the magnetic field. Causality means that
| energy is traveling away from the wire at the speed of light or
| slower. Therefore, the "expanding field" theory could make sense. But
| I've never found a calculation that would work to prove this. You try
| and nothing ends up making sense.

I'm not currently interested in trying to combine Lorentz and Faraday laws.
My interest right now is playing around with the Lorentz law and seeing
just what its boundaries are, especially with respect to the relativity
of motion. In other words, how far can I go with this concept of having
the magnets attached to the disk, and then modify the configuration beyond
the solid disk.


| Also as for Faraday Disks including the One Piece Faraday Homopolar
| Device (OPFHD) which means magnets rotate with disk. You CAN split the
| disk into radials or as Tesla proposed into a spiral which actually
| enhances the magnetic field as it produces current. It works the same.

That's an interesting one I had not seen. I looked at one patent Tesla
got that involved two disks edge to edge connected by some kind of belt
to make it easier to extract power. Back to Google.


| Yes then in the case of non-rotating magnets one actually can then say
| that the wires DO "cut" the flux. But in the one piece case, the
| problem is that you are using a loop to measure emf. One scenario is
| this: The magnet and the disk turn together. Therefore, there is NO
| emf induced into the disk no matter WHAT it's configuration! There is
| NO relative motion between them. The emf you are measuring is coming
| ALL from the wire loops hooked between the disk and meter. A similar
| argument ensues if you assume the magnetic field does not rotate with
| the magnet.

Are you saying this in terms of an argument one may face and have to ponder
or are you saying that the OPFHD really produces no EMF at all?

There is the counter argument that if the magnets rotate, and the disk
does not (wires are attached to measure), then this should induce some
voltage in the attached wires as well. Yet this configuration nets no
EMF.

But then, there is the counter argument to the counter argument that with
the magnets rotating, the disk is relatively going backwards with respect
to the magnets, and has an EMF in opposite polarity (compared to the disk
rotating and the magnets not) and this EMF bucks the EMF in the sensing
wires, resulting in nothing measured.

So which is it?

If the OPFHD really produces no EMF at all, then there was no paradox?


| These kind of experiments are easy to do. I've done quite a few. Just
| find some old dead large loudspeakers and remove the large ceramic
| disk magnets from them (they are usually glued in so it can take some
| work). Then set up your ideas. The voltages and currents from a
| Faraday disk should easily light most LEDs. But dig. They DON'T! All
| your various ideas somehow almost always seem to forget about the
| "complete" loop thing. The laws of line integrals in a conservative
| magnetic field are totally unforgiving! Nope, the LEDs do NOT light!
| Just gets you scratching your head. Evenually I had to join everyone
| else in the idea that the measurement cannot be made with a loop. It
| has to be made electrostatically. I don't like it, but it's just how
| it is.

I plan to buy some strong neodymium magnets to try things with when I do pick
an experiment to try.

I don't know what you mean by "measurement cannot be made with a loop". I am
not suggesting some kind of loop coupling to sense the EMF in the disk/wheel.

The loop is to generate a larger EMF potential. Putting the light on the
wheel itself is a means to directly measure without using brushes on the
disk.

I'm also considering the drum configuration. The conductors would run along
the drum parallel to the axis. The field would be radial to/from the axis.
And of course the motion would be circular around the drum.

--
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| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
.

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