Re: Filament resistance

[Allen Miller <amiller@suhep.phy.syr.edu>]

Joe,

The sun we see here on earth appears yellow, because the earth's
atmosphere scatters shorter wavelengths preferentially. In particular,
much of the blue light from the sun is scattered in random directions. 
The combination of red and green light that reaches our eyes is
responsible for the yellow color of the sun. On the moon, the sun appears
to be pure white. When one looks in a direction away from the sun, on the
moon, one sees only the stars and the dark sky. The blue component of the
white light seen from a direct look at the sun replaces the blue sky.

Allen Miller,
Syracuse University Physics Department 

On Wed, 8 Apr 1998, Joe Darling wrote:

> 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