PURPOSE: To show that hotter blackbodies radiate with shorter wavelength radiation.
DESCRIPTION: A variac is connected to two identical light bulbs in parallel, which are viewed behind red and blue filters respectively. As the voltage is increased by the variac, the lights glow more brightly, and more light is seen through the blue filter relative to that of the red filter. Very little or no blue is seen at low voltages, whereas red is seen to be emitted even at very low voltages.
REFERENCES: (PIRA unavailable.)
EQUIPMENT: Variac, light bulb and filter assembly with two clear 150 Watt light bulbs, red, and blue filters.
SETUP TIME: None.
Go back to Lecture-Demonstration Home Page.