PURPOSE: Demonstrate the change in the colors of the
continuous spectrum as the brightness of the source changes.
DESCRIPTION: A large filament lamp is connected to a variac. The
intensity of the source bulb is adjusted using a variac connected to the input to the
slide projector. As the light intensity is increased by the variac the spectrum becomes
more intense and also shifts significantly toward the blue. Increasing the source
intensity, and thus the blackbody temperature, shifts the spectrum to the blue (Wein's
Law) as the overall intensity increases (Rayleigh Jean's Law).
EQUIPMENT: Sun bulb, variac and prism, as photographed.
SETUP TIME: 10 minutes.