Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Re: Incandescent bulbs (was light bulb transient)



not only that, the emissivity changes and therefore, does not make a
black body source, contrary to PASCO's claim. The emissivity also
varies w/ wavelength. All this, and much more, is "nicely" graphed in
Levi's book. Also Levi gives the variation in current, luminous flux,
life, etc. as a function of the input V for tungsten lamps, I think both
for vacuum and gas filled (not xenon, probably N2?.

A fun xpt. is to plot the resistance of carbon fill. lamps [as a
function. of input V]

bc, been there done that.

p.s. the intermediate lab (still I think) at UCSC includes a nonlinear
section of the xpt. Low Freq. Impedances. They examine a thermister,
diode, and tungsten lamp. I was going to add an iron in vacuum? ballast
tube, but retired first. The contingently nonlinear elements are
especially interesting, as their behavior varies markedly w/ freq.
[Often requires hints from the TA]

p.p.s. A Prof.'s (at NPS) recent article in the TPT dealt w/ tungsten
resistance, if I remember correctly.

Quist, Oren wrote:
There has been a lot of interesting discussion about light bulbs. But,
no one seems interested in the overall change in resistance that must
occur -- or, perhaps I missed it.

I measured the (cold) resistance of a 60W bulb at approx. 19.4 ohms.

But, in operation (at 117 volts), the resistance will be approx. 230
ohms. This leads to a look at the temperature coefficient of
resistivity, which is poorly handled (it is not linear) in most lower
level textbooks.


Oren Quist
SDSU

_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l