My light bulb unit, mentioned by Leigh in his posting, is on-line at:
<http://www.sci-ed-ga.org/modules/materialscience/light/index.html>
The unit has connected investigations of 1 way and 3 way bulbs that
cause students to consider the temperature dependence of the resistance.
including a nice one on Tungsten filaments:
"The Coolidge Process for Making Tungsten Ductile: The
Foundation of Incandescent Lighting," C. L. Briant and B. P.
Bewlay, Materials Research Bulletin, August 1995, pp. 67-73.
Larry Woolf
General Atomics
www.ga.com
www.sci-ed-ga.org
-----Original Message-----
From: Leigh Palmer
Sent: Wednesday, November 16, 2005 10:35 AM
Subject: Incandescent bulbs (was light bulb transient)
This is just another item to add to a long list of interesting physical
aspects of what has unfortunately become a commonplace device in our
increasingly technically complex modern world. Larry Woolf is the light
bulb expert in this group, and if he didn't know about the 120 Hz
component before, he does now, and will include it in his next light
bulb book. The incandescent lamp was rightly hailed as a miraculous
invention when it was introduced, and there have been many improvements
to it since its invention.
In 1967 Mickey Walsh of the General Electric Research Laboratory pointed
out to me the one that is most stunning. Tungsten is a refractory metal,
yet it can be made ductile by a mechanical process.
This process was invented almost a century ago by William Coolidge, the
same person who invented the successful X-ray tubes that bear his name,
who also worked at GE. Ductile tungsten can be drawn into extremely fine
wires as it must be to make light bulb filaments. The next time you have
a burned out 115 V bulb, break it open and examine the filament
carefully with a 20x magnifier or better. If you have never done so, you
are in for a delightful surprise.
-----------------------------
-----Original Message-----
From: Quist, Oren
Sent: Wednesday, November 16, 2005 10:51 AM
Subject: Re: Incandescent bulbs (was light bulb transient)
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.
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