At this point I concede that I have no idea of the intent of the
original question. I went back and looked at it. It was posted on
5/19/99 by Randy Sloper and it says:
"Given two capacitors C1 and C2 charged to potentials V1 and V2
respectively determine the energy stored in them. Now connect the two
capicitors [sic] together positive to positive and determine the
potential difference and energy stored in the capicitors [sic]. If the
energies are different, where did the energy go?"
When I read this I imagined going into the lab, using real capacitors
with real wires and hence all the associated resistance, inductance,
etc. of that situation... hence I did not rule out I^2R nor LC
oscillations nor E&M waves.
Jack Uretsky imagined a more idealized situation in which the problem
was treated purely electrostatically and he ruled out things I did not
rule out.
Of my analysis Jack says, "That is not an appropriate analogy to a
problem that has been set up to make inductive effects insignificant."
And he also says, "...the problem is not posed as one involving SHM."
In the original problem I don't see any evidence to support Jack's
position (nor mine).
This reminds me of the problems students have on exams. Sometimes exam
writers don't want students to assume anything; i.e. can the student
work only with what is given. Other times the writers want students to
assume everything, and they want to examine the breadth of the student;
i.e. what insight from other situations can be brought to the question
under consideration.
I think it is possible the capacitor problem could be put on an exam to
see if students will think of I^2R and of LC oscillations. I also
think it is possible the problem could be put on an exam to see if
students would use Uretsky's approach. If we wanted to limit the
problem to electrostatics, we could choose wording to make that clear.
If we wanted to allow the other approaches it might be more difficult
to word the problem without giving away big clues. That is, it's
easier to tell students what approaches to exclude than it is to tell
them what approaches can be included (without giving away the answer).
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817