Re: A rotating disk PARADOX??

From: sal (believer_at_nospam.org)
Date: 07/07/04 

Date: Wed, 07 Jul 2004 07:41:11 -0400

I think you may also be asking about solid state chemistry.

My chemistry is 30 years out of date but let me try to clarify this a
little. In covalent bonds, roughly speaking, two adjacent atoms agree to
share a pair of electrons, and those two atoms are then bonded together.

In a "metallic" bond, all the atoms in a crystal agree to "share" their
outermost electrons. Those electrons, which are "communally owned", are
essentially unbound -- they can migrate freely through the crystal.

The electrons in a metal which are free to wander are referred to as
electrons in the "conduction band", which would be worth looking up.

The conduction band electrons, as a group, are electrostatically bound to
the crystal they're in, which is why they don't just fall out.

Those conduction band electrons form the "gas" I talked about in previous
posts. Their behavior is distinguished from the behavior of electrons
inside a superconductor in part by the fact that they undergo periodic
collisions with the lattice as they move through the crystal, which
converts their kinetic energy into heat. That's the source of electrical
"resistance".

On Tue, 06 Jul 2004 23:03:28 +0100, JM Albuquerque wrote:
>
> I can solve the same problem noting that around the wire (perpendicular to
> the main E field vector) there is a circular magnetic field that will
> interact with the main B field in such a way that it works exactly like
> conventional generators does.

My knowledge of E&M doesn't extend much above the individual
electron level, so it's my turn to say "Huh?"

You're modeling the behavior of a generator here using macroscopic
objects, and in that arena I've been told it's perfectly legitimate to
assign a potential energy to a (dipole) magnet in a magnetic field, in
which case, according to this model, the magnetic field is indeed "doing
work". But I'm completely unfamiliar with the details of this point of
view so I can't say anything intelligent about it. I will, however,
observe that this point of view is related to the elementary "eVxB" model
about as closely as organic chemistry is related to Schroedinger's
equations -- they're down there somewhere but you don't use them to figure
out if the solution in the test tube is going to turn blue.

> Note that ahead the wire you will have repelling magnetic poles slowing
> down the disk and behind the wire you will have attracting poles also
> slowing down the disk. Hence it is quit obvious that from this point of
> view it is the magnetic field that does all the work (the usual way -
> see stepper motors and reluctance machines, as well as induction and
> synchronous).
>
> So far we have discussed the generator problem. And what about the
> motor? Can you work out the same problem in the motor approach ? I guess
> not.
>
> If you apply a battery instead of the load the same disk must turn
> giving mechanical energy out.
> It is very easy to solve according to my explanation and
> straightforward. You apply the E field and a circular E field is created
> around the wire (radius).
> Then circular B field will interact with the main B field. Ahead the
> wire you will have repelling magnetic poles and behind the wire you will
> have attracting poles, hence the disk goes nice and easy. 

-- 
I can be contacted through http://www.physicsinsights.org

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