MadSci Network: Physics

Re: What causes incandescence/Joule heating: electronic or ionic movement?

Date: Wed Sep 20 10:35:25 2000
Posted By: Ronald Fisch, Physics, Washington University
Area of science: Physics
ID: 966734557.Ph

Since one wants to run an electric current through the filament,
it is made out of a good metal.  Usually tungsten is used, because of
its high melting point.  The electromagnetic emission of such a filament
in the visible range is dominated by the contribution from the
conduction electrons.

The vibrational spectrum of the crystalline ions is in the infrared,
not in the visible range.  The electromagnetic emission in the infrared
is usually dominated by these vibrations of the ions.

At 300 Kelvin (room temperature) most of the power is emitted in the
infrared, so the ionic contribution dominates.  But at 3000 Kelvin
(which is a reasonable estimate for the operating temperature of a
light bulb filament) most of the power is in the visible, so the
conduction electrons dominate.

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