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Re: R = V/I with real lightbulbs



I (assuming I haven't missed a post) am surprised no one has compared ohms law to another
law. Hook's law! I invite a rancorous debate on how it's not a law either.

bc


Gary Karshner wrote:

I finally have time to put my foot into this mess.
William Lichten in his book "Data and Error Analysis" gives as an example
the current verses voltage relationship for a tungsten lamp from an applied
voltage of 30 mV to 5.3 volts. The log-log graph starts out with a slope of
about one (where Ohm's law is approximately correct) and then at higher
voltages it shifts over to about a 5/3 power law relationship where
radiation cooling becomes important. It is a nice example of how different
relationships are at work depending on the physical conditions of the system.
Ohms law like almost all laws trying to describe the physical proprieties
of matter is an approximations at best. In physics we start with simple
systems and then relax the constraints to cover a wider and wider range of
conditions. I have always been impressed that Ohm's law which only works
for a limited range of materials (conductors) over a limited temperature
range works well enough that the whole electronics industry is based on it!

Gary

Gary Karshner

St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU