Re: There's work, and then there's work

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

On Tuesday, Jan 28, 2003, at 11:52 US/Eastern, David Rutherford wrote:
>

> I was hoping to get an answer to this question. Is it valid to combine
> (add) the results of both experiments if they are done at the same time
> on the same circuit? If not, why not?
You are correct that two experiments can be performed at the
same time. I would suggest one modification. But be careful
that your galvanometer, if that how you measure i several
times while a large capacitor discharges, has an R2 that is
very small in comparison with the R1 inside the calorimeter.
On the other hand, too large R1 and too large C can lead
too long cycles; you want to finish the experiment faster
than too much heat escapes from the calorimeter.

You can avoid this dilemma by not using a galvanometer.
Measure U on the capacitor (same as on R1) with a voltmeter.
Then calculate instantaneous i=U/R1. The impedance of the
voltmeter should be much larger than R1. This will not be
hard to satisfy with a common instrument. An oscilloscope
with memory is also a possibility (to record U, for example,
every two seconds) but such instruments are not common.

But do not forget that other contributors to this thread are
going to wait for the experimental resolution of your
dilemma. Do not disappoint us.
Ludwik Kowalski