This demo shows the shifting colors as a function of filament temperature. Also, this demo shows prism dispersion, radiation intensity as a function of wavelength, and infrared radiation. The black body radiation curve can be demonstrated by using a radiation sensor hooked to a digital millivoltmeter. The carbon disulfide prism (see Dispersion) is used to spread out the light of a slide projector lamp onto a screen . As you scan across the spectrum with the radiation sensor, the millivoltmeter shows the peak of the 3000 K tungsten filament in the infrared with the tails of the curve in the visible spectrum and further infrared.
The same demonstration can be done more qualitatively. Turn down the room lights and show the spectrum of "white" light on the wall. As you reduce the voltage to the lamp with the variac, the blue color dies away, and then the green, leaving only dull red of low intensity. (Of course, the 3000 K tungsten filament already peaks in the infrared so the initial "white" light is already quite red. Infrared itself can be demonstrated; see Infrared, Radiometer, and Maxwell's Spectrum)
The applet below shows the blackbody curve and colors corresponding to the given temperature. |
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