Re: Bending of Ohm's Law was Re: Gap Question

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Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


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From: "Tesla list" <tesla-at-pupman-dot-com>
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Sent: Saturday, February 28, 2004 9:10 AM
Subject: Re: Bending of Ohm's Law was Re: Gap Question


 > Original poster: dave pierson <davep-at-quik-dot-com>
 >
 >
 > >Awesome!!
 > >Any idea where I could find a V I curve chart for a standard light bulb?
 >
 >     Its a straight line.  A resistance.
 >     (pause...)
 >
 >     AT ANY ONE TEMPERATURE.
 >        (To fully plot it, or any, needs a 3D graph...
 >         with temp on the other axis...)

Nope.. at a constant temperature of the bulb, a tungsten filament bulb will
have a very nonlinear V/I curve (reflecting the temperature of the
filament).  To say that it is linear at any specific temperature of the
filament is pointless, since there is only one combination of V and I that
will achieve that temperature, so there's no relationship to be linear or
nonlinear.

yes, one could conceive of a scheme where one heats a filament by adding
power externally, to hold it at constant temperature, and, in fact, if you
can do that, you will have a linear resistor.  Oddly, though, in practice,
one measures the temperature by measuring the resistance of the filament,
and adjusts the power accordingly.
This single value behavior is what folks making precision (<0.01 dB) RF
measurements depend on with using thermistor probes by the DC current
replacement technique.