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Re: "Charged" capacitor mis-terminology



Hi Don,
Students have mis-conceptions and erroneous notions - agreed!
Changing a word (especially this one) is not the cure - the word wasn't the
cause.
By the way, it is not unusual to consider a non-neutral capacitor in my
class ( or a "capacitor" consisting of three separated conductors).

Over-insisting on proper words (akin to proper penmanship) is often part of
the problem of not concentrating on clarifying ideas. A teacher who would
insist on such a narrow use of "charge" has a narrow view of the reality in
discussion. Any imaginative and fertile mind sees, and uses, many uses for
almost all words. Of course there are excesses in both directions, but we
are limited to 26 letters and 10 (decimal) integers.

(We are not limited to only one model, be it mathematical, conceptual, or
"lingual".)

If you had a congenitally blind student, would you insist that he mouth all
of your models?

What two not uncommon English words have identical pronunciations and
spellings but opposite meanings? (As far as I know, this amazing discovery
is original!)

(I hope those were not real test questions you presented.)

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


-----Original Message-----
From: Donald E. Simanek <dsimanek@eagle.lhup.edu>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>
Cc: PHYS-L <phys-l@atlantis.uwf.edu>
Date: Sunday, February 15, 1998 12:07 AM
Subject: Re: "Charged" capacitor mis-terminology




On Sat, 14 Feb 1998, Bob Sciamanda wrote:

I'm sorry, but I really think this objection is silly. In almost 40
years
of teaching physics I have never known this phraseology to be
mis-interpreted, nor did any danger of this happening ever even occur to
me
until I first saw it exposed on this list. A language which can
peaceably
live with "lb." as the abbreviation for "pound" has long since learned
that
there are more serious battles to wage than the proper choice of a
harmless
sound.

-Bob


Maybe we don't ask the right questions to find out whether students
mis-interpret. If we just ask them to calculate C given V and Q, or some
variant of that, they may well get the right answer without relying on any
conceptual model. What if we ask:

The process of charging a capacitor means that
a) charge is created within the capacitor.
b) charge is added to the capacitor from outside.
d) current is stored in the capacitor.
e) charge is converted to voltage in the capacitor.
f) charges within the capacitor are relocated to positions
of greater energy.

You may find ways to imporve or refine the wording. But I suspect that
many students would choose (a) or (b).

Change "capacitor" to "battery" and you'd likely reveal similar student
confusion.

Another question to reveal misconceptions:

Consider a resistor carrying current in a circuit. The resistor warms up,
indicating that some of the electrical energy is converted to thermal
energy. Assuming that the current consists of electrons moving through
the resistor, where does this thermal energy come from?
a) Electron-positron pair annihilation.
b) The kinetic energy of the electrons decreases, slowing them up.
c) The potential energy of the electrons decreases as they pass
through the resistor.
d) Electrons bounce off of each other inelastically.
e) Electromagnetic field lines flow from the battery through the
wires into the capacitor where they get all tangled up and can't easily
get out.

Again, I'm not totally happy with the wording. But I know many students
would like (b). I hope none choose (e).

We often aren't aware of student misconceptions because we don't ask
students the questions which could reveal them. I'm convinced this is why
some courses with content and teaching methods I find deficient can claim
great success in student performance. Ask the "safe" questions and almost
any course can appear to be a success.

There's a semantic problem with resistors which I only recently became
aware of. Students sometimes think that a resistor "reduces the current".
Compared to what? The student may be confusing two things: (1) A branch of
a circuit is opened up and a resistor placed there. The presence of the
resistor causes the current in that branch to be less than it was when the
resistor wasn't there. (2) The current "coming out" of the resistor is
less than that "going in". No. 1 is essentially correct in most cases that
the student experiences, while No. 2 is wrong.

No 1 is not correct if the branch is directly from a curent-regulated
power source.

When we say "reduced" we need to be very specific what two things we are
comparing.

-- Donald

.....................................................................
Dr. Donald E. Simanek Office: 717-893-2079
Professor of Physics FAX: 717-893-2048
Lock Haven University, Lock Haven, PA. 17745
dsimanek@eagle.lhup.edu http://www.lhup.edu/~dsimanek
.....................................................................