Re: Thermodynamics and Lenz's Law

["John S. Denker" <jsd@MONMOUTH.COM>]

At 03:43 PM 3/9/01 -0500, Peter Schoch wrote:

> ... Lenz's Law for
> Induction.  He wanted to know if somehow it was tied to the idea in
> thermodynamics that no "engine" could be 100% efficient.  His reasoning
> was that if The induced current wasn't in opposition to the inducing
> flux, we could create a perpetual motion machine which would violate
> entropy.

There are a couple of confusing elements to the question.  Let me try to
untangle them.

1a) At one extreme we have arithmetic, where 2+2=4 pretty much exactly.

1b) In real-world physics (or in real life in general) there are lots of
things that aren't 100%.  Rulers are never 100% straight.  Wheels are never
100% round.  This usually has nothing to do with thermodynamics.  Usually
you can get very close, often arbitrarily close, to 100%.

1c) At the opposite extreme, thermodynamics is interesting because it can
make statements such as
       "This heat engine will never be more than 40% efficient."

That is wildly different from saying that such-and-such will never be 100%
efficient.

So there is really not any useful connection between Lenz's law and the 2nd
law of thermodynamics.

==============

2) On the other hand, there is always the first law (which in my book is
nothing more or less than the law of conservation of energy).

If you could make something with negative Lenz-law behavior, you could put
two of them next to each other, and then the field of one would cause the
field of the other to grow.  You might need to "tickle" the system with a
small field to get things started, but then things would grow _ad infinitum_.

This would violate the _first_ law.