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

["Tesla list" <tesla-at-pupman-dot-com>]

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,
    Which is marginally relevant.
    Clearly the temperature of the _filament_ is what is of interest.

 >> a tungsten filament bulb will  have a very nonlinear V/I curve
 >> (reflecting the temperature of the  filament).
       If the temperature of the filament be changed.

 >>  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
    There are a huge number.
    For a 110v lamp, use 1v, 2v, 3v, etc.
    The temp of the filament will vary little, if at all.

 >> that  will achieve that temperature,
    cf as above.
    I will offer to make the measurement at 110v if allowed a large
    enough heat sink.  And likely some LN2.


 >> so there's no relationship to be linear or  nonlinear.
    There is, if the experiment be designed to find it.

 > > yes, one could conceive of a scheme where one heats a filament by adding
 > > power externally, to hold it at constant temperature,
    Which is another way.  Or removing enough  heat (cf my
    heat sink....)

    The objective was to study the filament, rather than the lamp.

 >>and, in fact, if you  can do that, you will have a linear resistor.
    yep.

 >>  Oddly, though, in practice,  one measures the temperature by measuring
 >> the resistance of the filament,  and adjusts the power accordingly.
    Depends on what is of interest.

 > > 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.
    Indeed.

 >     I think constant FILAMENT temperature was what was implied there.
    Yep.  I never said bulb (tho i ALSO did not say filament...)

    best
     dwp