Re: Battery connection

[brian whatcott <inet@INTELLISYS.NET>]

At 00:11 8/4/01 -0400, Ludwik was looking for an introductory
electrochemical cell model when he remarked:
> /snip/
> My impression is that electrochemical cells can not be explained
> at the elementary level
/snip/
> Ludwik Kowalski

For a teacher dealing with students who can find value in water flow models
of current electricity, perhaps proceeding from some observed effects to
a basic model might be helpful.

 If we remark that a metal when heated red hot first parts with
 electrons, then with molecules and note that some metals dipped
in conductive solutions seem to part with charged particles,
then with molecules and some materials when sheared or rubbed
 seem to part with charged particles at the interface, and when
a pointed electrode is charged to 6000 volts it is capable of
splitting air into charged parts and when charged to 8000 volts
it is capable of changing  oxygen molecules to ozone molecules
there is evidence for the possibility of parting materials not
 only cleanly by molecule, but with more ragged or atomic
effects of an electrical kind.

We might note in passing that even though the packets of energy
in a light beam are proportional to the beam's color or frequency,
there is some color which comprises packets not energetic enough to allow
surface electrons to escape photoelectrically from a metal.

We could say there is some temperature below which electrons cannot be
electrically attracted away from a heated metal glowing in a vacuum.

 In the electrolytic context, perhaps it should be unsurprising
that different metals dissolve at different rates, so that they might
be expected also to exchange charge with a solution at different
rates with the consequence that the relative voltage between
two electrodes grows until the charge transfer is limited by some
electrochemical effect acting in the opposite direction which
is measured as an open circuit voltage.

We could say that when zinc and copper (or carbon) are dipped
in an electrolyte, the zinc is consumed when an external current
 is taken, so that the zinc if used as a cylinder finally develops
 a hole, the electrolyte runs out and spoils its surroundings
unless the zinc container is capsulated in steel or plastic.

We might say that if pairs of metals are tested they can be
ranked in a potential or activity order:

potassium
calcium
sodium
magnesium
aluminum
zinc
cadmium
iron
nickel
tin
lead

copper
mercury
siver
platinum
gold

This suggestion sweeps together effects of various kinds,
but could possibly provide some intuitive support to students,
without undue conflict with more elegant models to be
developed later.