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Re: The conceptual change process (long)




-----Original Message-----
From: William Beaty <billb@eskimo.com>
To: list physics teaching <PHYS-L@atlantis.uwf.edu>
Date: Tuesday, February 17, 1998 3:46 AM
Subject: Re: The conceptual change process (long)


On Sun, 15 Feb 1998, Bob Sciamanda wrote:

Bill,
Had you been my student, you would have examined the details. You
were
taught (or at least learned) words, not physical phenomena.

Bob,

The trouble is, I DID examine details. As I student I used H&R, and as
part of electronics classes I did lots of capacitor experiments. But
the
particular way that my mind "pigeonholed" the information was the cause
of
the problem. I see that all this happened on a conceptual level, not a
level of words. My concepts were fine, it was my "concept net" that was
a
horrible mess. Things didn't connect. My analogy for a capacitor was
that of a charge-filled bucket, when it should have been that of a
stretched rubber band, or of a membrane between two water-filled
chambers.
The bucket-metaphor made me misinterpret everything.


Why not the analogy of two separated conductors with some electrons
transferred from one to the other. ("The best model for a cat is another
cat, or the same cat .") or . . (crutches and analogies are to help the
crippled . . . this concept is not crippled.)
Analogies can do more harm than good. . . if the concept itself is
scrutable, let it speak for itself.

. . .
Don't rely on
words (or mathematics) alone to convey or express the physics; they
must be
chewed, ruminated, digested, purged of waste materials, and only then
assimilated into our being. Whatever word choices we make, they too
are
faltering, incomplete (linguistic) models for ideas (which themselves
are
models of reality).

My arguments center around my recent activities in journeying back into
my
earlier physics learning experiences and their results, and my discovery
of a major distorting concept in myself. I had originally failed to
chew
and digest old concepts. I could use the concepts, but realized that
something was seriously wrong. When I went back and sorted things out
(with the benefits of having worked on K-6 misconceptions), I extracted
a
single large monkey wrench that had been lodged in my "concept digestion
mechanism." . . .
. . .
I think that analogies illustrate the flaw more clearly. If I stake
down
the ends of a rubber band, then grasp the center of the rubberband
between
thumb and forefinger and move it towards one of the ends, have I "stored
rubber"? No, because every bit of rubber that was removed from one
side,
was placed into the other side. Considered individually, one side of my
rubber band has less, and the other side has more, but no rubber has
been
created, destroyed, or added. If I boost an atom's electron from a
lower
shell to a higher, have I injected charge into the atom? Is the atom a
device for storing charge, or does it have constant (but energetically
reconfigurable) charge? Is my rubberband a device for storing rubber,
or
does it have constant (but energetically reconfigurable) quantity of
rubber? Do we usually reconfigure the charges in a capacitor
energetically, while simultaneously leaving the capacitor neutral before
and after? I'd say yes.


You seem to have no tolerance for using a word or phrase in a way which
is not identical with its "root" meaning. I'm afraid you'll have to
develop that tolerance (imagination?), not just for technical (or poetic)
usage. It happens in common usages; phrases come and go (make a study
of teen age speech through the years); technical vocabularies seem to
come just as capriciously but then tend to stick (because, whatever it
is, we need a stable language)!

A capacitor is a thing; in the most common use of the word it is
a system of two conductors, electrically insulated from each other.
Many
things can be done to/with this thing; the two conductors can each be
electrically charged in a wide variety of ways. Such a physical
discussion
should be engaged (and played with in electrostatic experimentation -
real
and/or gedanken) long before the concept of "capacitance" as a
definable
property of a properly designed system subjected to a definite
procedure is
created.

True, and the bulk of my comments are regarding a 2-plate capacitor.
This
is different than the "3 metal sphere capacitor." . . .

. . .
If I take a long view regarding these messages, I note that what I'm
doing
is to insist that all explanations of capacitors stringently stay
consistent with the conservation law. If we place equal (+) and (-)
charges into any device, then we damn well better NOT say that we have
injected any charge into that device. Putting in the (+) may increase
the
charge, but putting in the (-) decreases the charge again.
. . .

Why is it necessary to explicitly pledge allegiance to the conservation
law every time we speak of a capacitor? Could we change this language if
tomorrow the conservation of charge were disproven? The useful property
of the capacitor is that the transfer of a charge from one plate to the
other always results (if well designed) in a proportional potential
difference from one plate to the other. So Q, the quantity of
transferred charge, is a natural state variable, both mathematically and
linquistically.

. . .
William J. Beaty SCIENCE HOBBYIST
website
billb@eskimo.com www.eskimo.com/~billb
EE/programmer/sci-exhibits science projects, tesla, weird
science
Seattle, WA 206-781-3320 freenrg-L taoshum-L vortex-L
webhead-L

I truly appreciate your difficulties, Bill. You are certainly not alone,
and noone should make light of these problems. But I sincerely believe
that the root problem is often traceable to a common and dangerous human
tendency to succumb to the tyranny of words. Make words (and numbers)
your servants, not your masters; your students, not your teachers.

-Bob

Bob Sciamanda sciamanda@edinboro.edu
Dept of Physics trebor@velocity.net
Edinboro Univ of PA http://www.edinboro.edu/~sciamanda/home.html
Edinboro, PA (814)838-7185