Re: Inertia and Lenz's Law

[Doug Craigen <dcc@cyberspc.mb.ca>]

>  Also, he said the demonstration where an aluminum ring is placed on 
>  an iron core stand that is surrounded by a transformer coil does not >  truly demonstrate Lenz's Law.  What is your sense on this one, too.

What is demonstrated with the aluminum ring?  I know of a couple of
things:

One is joule heating from the induced current.  

The other is turning the rings into projectiles.  The latter effect is 
more complicated than what I usually hear as an explanation.  Yes a
current is induced, turning the ring into an electromagnet.  However,
why does this cause it to accelerate along the stand?  One might expect
the effects to cancel, being ac and all, but doing the math with a phase
difference between the induced field current and applied field, one
finds a net non-zero effect.  Now why does this effect accelerate it
along the stand?  A ring carrying a current in a uniform magnetic field
would have a prefered orientation, but not an acceleration in any
direction.  I expect the answer is related to how the magnetic field
dies off with distance away from the transformer.  Hence the trivial
explanation of "the oscillating magnetic field induces a current,
which is then repelled by the magnetic field" has a few gaps in it.
 
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| Doug Craigen                                                 |
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