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Re: Physics Laboratory Design




On Thu, 15 Oct 1998 02:50:19 -0500 brian whatcott <inet@intellisys.net>
writes:

A current is passed through a long wire, a stainless or piano wire
that either sags or is tensioned with a spring. The wire grows red hot.
Then the current is cut off. The writers report that the wire cools to
a dark color, >then briefly glows red again; meanwhile the wire shortens,
extends reflexively >then cools.
Others describe the varying sag. This was (is?) offered as a change
of state latent heat, a curie point issue etc....

I remember how much I enjoyed seeing this demonstration several years
ago. The explanation that was given suggested that the wire contains
electrons in face centered crystals that change to body centered crystals
at the Curie temperature. Because the packing of these crystals is
different, the wire sags or tightens and gives off extra energy (as heat)
in the process of changing.

Herb Gottlieb from New York City
(Where physics demonstrations used to get the students much more excited
than they do now)