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Re: R = V/I ?

OK, so this is all somewhat circular. However, once experimentally
measured, the resistivity and the coefficient can be considered to be
properties of the material and the length and area as geometrical factors.
I would then much prefer to think of RESISTANCE as DUE TO the properties of
the material and the shape of the object than being DUE TO the Voltage
applied across the material and the subsequent flow of current. Perhaps
this is just semantics, but I don't think so. There seems to be to be many
pedagogical traps with DEFINING resistance as V/I---IMO.

Rick


----- Original Message -----
From: "Mark Sylvester" <msylvest@SPIN.IT>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, May 05, 2000 1:25 PM
Subject: Re: R = V/I ?


At 12.59 05/05/00 -0500, Richard W. Tarara wrote:
----- Original Message -----
From: "Mark Sylvester" <msylvest@SPIN.IT>

Hmmm... what, then, is the quantitative definition of R?

Mark

For a uniform material, I would use:

R = Resistivity x Length/ (Cross Sectional Area)

where the Resistivity = (Temperature normalized Resistivity)(1+alpha x
deltaT)

alpha being a measured/cataloged coefficient and deltaT measured from the
normalization Temp (often 20C).

For a complex object, the resistance is a parallel/series combination of
these terms depending on the materials and the construction. Again, V/I
can
functionally give you a _measure_ of the resistance of such an object,
but
doesn't (in my mind) define that resistance.



... and the "Temperature normalized Resistivity" is defined without using
the concept of resistance or its equivalent?

Mark.



_____________________________________
Mark Sylvester
United World College of the Adriatic,
34013 Duino TS, Italy.
_____________________________________