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Re: Batteries



While you never used the word work function, in a solid metal, the
highest filled energy level is related to the work function, since the
latter is the energy needed to extract an electron from the metal...so
there is a sense in which it corresponds to the ionzation energy for the
atoms you are talking about in your model.
Having said that, my concern is more fundamental...it is not at all
clear to me that contact charging can be explained by the process of
electron transfer...whatever model you use to represent it.
That is the evidence I am asking for...that indeed contact
electrification occurs by electron transfer, as opposed for example to
ion fragment transfer.
Any real material has a surface which is not what is in the bulk, since
there is lots of chemistry at the solid surface not to mention the
organic gooh that covers everything. Usually one half of the rubbing
combination is a polymer of some sort. The energies needed to transfer
ion fragments is lots less than the energy needed to transfer electrons,
even if you allow for unlikely quantum tunnelling. This is not original
with me...read Sherwood and Chabay.

I just don't think there is good evidence to support an electron
transfer model.

cheers,

joe

On Wed, 13 Feb 2002, Bob Sciamanda
wrote:

I never used the word "work function". Please argue to the statements
below. (I am not being belligerent - I want to learn.)

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Joseph Bellina" <jbellina@SAINTMARYS.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, February 13, 2002 2:18 PM
Subject: Re: Batteries


This is all well and good if work-function difference is a good model
for explaining charging by contact in the real world.
Anyone care to defend that position, because I don't think it is
defendable.

joe

On Wed, 13 Feb 2002,
Bob Sciamanda wrote:

Ludwik wrote:
. . .And I do not remember any explanations of the electrification
by contact, only a description of it. Therefore I still feel that I
have nothing to lean on when trying to explain the nature
of something that takes electrons away from Cu and delivers
them to Zn via salty water. . . .

This is a perennial, sticky problem, ignored in any useful way by
texts.
As a stab at the suggestion of a beginning to an approach, consider:
1) Assume students have studied the discrete energy levels available
to
electrons in a square well potential or in the electrostatic potential
well of a nucleus.
2) They recognize that in each of these situations there is a lowest
possible (ground) bound energy level, and a highest possible bound
level
(below the continuum of positive energies). They also appreciate that
(neglecting spin) only one electron may occupy a particle state.
3) Now consider an electron sitting in the ground state of a hydrogen
nucleus' potential well.
4) Suppose there is available a second, different nucleus with a
deeper
well. Suppose that this second system has unfilled electron states
available with energies lower than the hydrogen ground state energy
(an
energy level diagram helps here).
5) If there were available a way for the hydrogen's electron to move
into
the second nucleus' well, it could get rid of some energy. In its
effect,
this is equivalent (perhaps not in the Newtonian sense, but in the QM
sense) to a force attracting this electron into the second well.
6) . . . go on to salt bridges between dissimilar metals, etc (?)

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor


Joseph J. Bellina, Jr. 219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556


Joseph J. Bellina, Jr. 219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556