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Re: R = V/I ?



I suppose that we would have to say that in this case the input device
is a potential (probably variable) in series with an impedance. I
cannot image how we could get by without some resistance unless the
input device is superconducting.

Now, how about the definition of resistance as V/I. This can be
interpreted it two ways depending on what kind of measurements are made.
If we have some kind of passive device and measure a set of points {
V1, I1; V2, I2; V3, I3........etc) we can define the resistance at
each point from the ratio of V to I, but it may turn out that the
resistance at each point is different. We might also define a
resistance from the slope of the V vs I curve and these resistances
might be different at each point.

What can we say then. Perhaps we might remark that the usefulness of
the concept of resistance depends on how nearly constant these
definitions of resistance are. That is the reason that we attempt to
control or measure the temperature. We have discovered that the
temperature of the conductor has an influence on its resistance. We
have also discovered that different materials change resistance in
difference ways - interesting for the study of materials, but I fear I
am rambling. WBN

Barlow Newbolt
Professor of Physics
Washington and Lee University
e-mail: newboltw@wlu.edu
telephone: 540-463-8881
fax: 540-463-8884
Office: Howe 218

"Had I been present at the creation, I would have given
some useful hints for the better ordering of the universe."

Alphonso X, Learned King of Spain (1252 - 1284)