Light from Heat
Robert Elliott
Award: Top 100
School: glenbard west high school
Teacher: nicholas szarzak
Category: Contrived
Photo #21052
Light from Heat
This is a tetrode (4-electrode) vacuum tube, with a significant current causing its filament to glow. Although this seems ordinary (a red-hot piece of metal), the details of the process behind this are remarkable.
All objects emit electromagnetic radiation known as black-body radiation. (An ideal black body, which can be approximated by a cavity with dark black walls, is the perfect absorber--and radiator. If electromagnetic radiation were introduced to it, it would be absorbed, raising the temperature of the black body.) This radiation is mostly infrared (radiant heat) at room temperature, but as an object's temperature is increased the radiation's frequency distribution begins to reach higher intensities at shorter wavelengths. This is why the filament of this vacuum tube is glowing--a significant amount of heat is produced in it through Joule heating, and, as its temperature increases, the wavelengths of the radiation become shorter, moving from infrared to visible light and causing it to glow.
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