INFRA-RED ABSORPTION AND EMISSION
: ILLUSTRATE HOW LIQUIDS AND SOLIDS INTERACT WITH IR RADIATION.
These demonstrations use different heated materials to illustrate emissivity
in the IR and IR absorption.
The various pieces (cartoon, above, and reality, below).
- Using the temperature controlled hot plate heat up black or silver plates
to 250 or 300F. USE HEAT RESISTANT GLOVES.\
- Measure the T of the black plate. It agrees with heater
setting. Measure though a plastic bag and a bag filled with
water. Show that water is a good absorber of IR.
- Measure effective T with IR thermometer (10 microns). Silver plate
measures way too low.
- However silver plate with a water layer on top measure boiling point
(water boils when placed on the silver plate, showing that it is much hotter
than IR measurement suggests). Shows that water is a good IR emitter
(and absorber, see above, a la Kirchoff), even though it is transparent in
the visible.
©2000.
John Hart, University of Colorado