electronic components

[kowalskil@alpha.montclair.edu]

The reply to John, and the follow-up message, were posted early this
afternoon but nothing bounced back to me. I am posting these two messages
together again. Sorry if you receive them twice.        ludwik
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On 29 Dec 1996 John Mallinckrodt wrote:

> When I fit exponential functions to either of your sets of current data
> and integrate them, I get charges of just under 6 C--not different enough
> from the nominal 5 C to concern me greatly. 

One of us made an integration error. I will check my part and report the
result very soon.

> In your message of 12/26 you say that you get your value from a *linear* 
> fit to the data.  If so, that certainly would explain the problem!

Well, I did not say it right. I ment to say that I plotted I=f(t) as a
linear (not semi-log) graph. Then, instead of integrating numerically,
I simply counted the number of squares. Perhaps I made an error in 
assigning the number of coulombs to one square. I do not think so, but
let me verify.
                 Ludwik Kowalski       kowalskiL@alpha.montclair.edu
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Yes John, I goofed. And I agree that a capacitor, nominally 1 F, can in
reality have C=1.2 F. Thanks for correcting me. This takes care of my
"non-electric" energy concern. 

Like you I have no answers to the described properties of new caps. But 
some of phys-L-ers are very knowledgable and can help us to understand 
the situation. Here are my questions:

  a) Why are the discharging and charging curves non-exponential?
  b) Why is the effective R*C correlated the magnitude of I?
  c) Why do we observe "residual voltage"?
  d) What kind of hysteresis are we referring to and what causes it?

As a physics teacher I am sensitive to all significant discrepancies 
between what we teach and what happens in reality. It bothers me that a 
unit called capacitor does not discharge exponentially through a resistor. 
The factor of 2 or 3 in the effective R*C is very significant and I would 
like to understand it. (When a cannon ball does not travel along the
idealized parabolic trajectory I say "air resistance". I would like to
have something like this for non-exponetiality, and for other things.)  

Supercaps seem to be highly suitable for student-bsed research; the 
equipment needed to study them is available in most of our labs. We need
topics of that kind. It is fun to play a scientist. I hope this is not 
an end of the thread.

Ludwik Kowalski      kowalskiL@alpha.montclair.edu
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