Re: Filament resistance

[Joe Darling <jdarling@emh1.otc.cc.mo.us>]

This discussion has raised in my mind the following question that has
occured to me before.

The surface of the Sun is about 5800 K and emits spectrum of light that
has a yellow cast.  The filment of a light bulb, if made of tungsten,
could not be hotter than 3695 K, its melting point, and yet emits light
that appears white, even in the small clear bulbs used to demonstrate
series and parallel circuits.  The white light should indicate that the
tungsten is at a higher temperature than the surface of the Sun.  What am
I missing here?

Joe D. Darling   jdarling@emh1.otc.cc.mo.us
Instructor of Physics and Physical Science  
Ozarks Technical Community College
1020 East Brower   Springfield, MO 65802
(417) 895-7907   (417) 895-7085 FAX

On Tue, 7 Apr 1998, Daniel L. MacIsaac wrote:

> > You took the power dissipation when incandescent, and the Rho for room
> > temperature. The temperature range is so large and somewhat non-linear too
> > that this leads to large errors.
> >
> >  Jones & Langmuir published this:
> > temp K    Resistivity (micro ohm cm) (NOTE UNITS)
> > 300       5.65
> > 1000     24.93
> > 2000     56.67
> > 3000     92.04
> >
> > (If you feel this critique is cogent, perhaps you would write the 
> > publishers, as a public-service.)
> >
> > Whatcott    Altus OK
> Brian,
>
> Thanks for the improved rho values; I appreciate your effort finding them
> and setting the record straight (por improving it).  It'd still be nice to
> have a geometric determination of the length of that wire spiral as well.
>
> I agree with your and Leigh's comments.  I'd feel happier if I knew the WHOLE
> picture, including a correct temp for the filament (is 3000K the photo
> standard?) and a better value on the diameter of the filament.  As well, the
> composition of the filament -- is it really just W?
>
> At that point I'd contact the publishers.  It'd be nice to suggest a complete
> appropriate (and cogent :^) correction at once.
>
> Dan M