Re: delta V = I R

[Bob Sciamanda <trebor@VELOCITY.NET>]

Hi Paul,
It goes without saying that vendors/manufacturers of "resistors" (two
terminal devices with a specified numerical value of R under a practical
range of V) would choose a material and construction designed to assure a
"constant" R specification.  That forced choice should not be extrapolated
to a general property of materials.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: Paul O. Johnson <pojhome@FLASH.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, November 08, 1999 3:03 PM
Subject: Re: delta V = I R


> Bob Sciamanda wrote:
>
> > R can depend on many things, often usefully so, eg: photoresistive
devices
> > (like CdS) have light-sensitive resistance.  Bulk materials even have
> > non-isotropic resistance (best described by a matrix).  An Ne2 neon
bulb has
> > almost infinite resistance below a firing voltage (c. 75 Volts), above
which
> > it is almost a short circuit.  A gas discharge can even have a
negative
> > DYNAMIC resistance (as can a tunnel diode).
> >
> > Some gas sniffing detectors rely on resistance changes in the presence
of
> > certain gases (often as the result of a chemical reaction.
>
> Thanks for your reply, Bob. I am familiar with these devices, but when I
asked
> my question (admittedly not stated very well) I was thinking of carbon
or wire
> wound resistors.
>
> poj