Re: Light bulb science and technology

["Daniel L. MacIsaac" <Dan.MacIsaac@Nau.Edu>]

> to appreciate just how amazing the tungsten light bulb filament is, I
> urge every physics teacher to make the small effort required to look
> closely at the filament from a 60W or 100W light bulb. Break a burned
> out bulb to get at it; you can't see it though the envelope without a
> good long distance microscope. A good hand magnifier will serve to
> reveal the structure, but a stereo microscope is better if you have
>
> Leigh
....I second this.  In the 4th Ed of Cutnell & Johnson, students calculate
the length of a Tungsten filament in a 150W light bulb as 11m.  Nonsense,
says I -- another atrociously bad text problem.  Then I recalled Leigh's
comments on filaments from Phys-L several months back.  So I do the 60W
bulb calculation (still several m of filament); break it open and examine
the filament under a 30X hand microscope.  It's all there!!!  And I used
to joke about installing car radios in Japanese cars :^)  C&J and
Leigh have it right -- if you haven't examined a filament under a 
low power microscope yet its time you did.

Dan M

Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu  http://www.phy.nau.edu/~danmac/homepage.html