Re: delta V = I R

[Richard Tarara <rtarara@SAINTMARYS.EDU>]

----- Original Message -----
From: Michael Edmiston <edmiston@BLUFFTON.EDU>

> Not only should we think of Ohm's law as delta-V = IR, we should also
> remember that the real "meat and potatoes" of Ohm's law is that R
> should be constant.  Or, better stated, that current through a device
> is a linear function of the potential difference across the device.

The only problem with this is when we go into the laboratory with intro
students.  Yes we would like to take data, have them plot it, have it be
linear, and have the slope end up the value of the resistance.  The problem
is, what is normally done is to vary the potential difference (V) and
measure the current (I).  The standard plot should then yield I = (1/R)V.
The slope is 1/R (or as our Chemistry friends would say--the conductance).
We can always have them plot the data as V vrs I, but even many of the intro
students know that's not 'correct' in terms of the experiment.  **I have the
same problem with a N2 experiment where we vary the applied force and
measure the acceleration but we really want to plot F vrs a so that the
slope ends up the mass of the accelerating system.**

Rick

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Richard W. Tarara
Department of Chemistry & Physics
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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