PURPOSE: To illustrate focusing of heat in a very dramatic way.
DESCRIPTION: This demonstration uses one of the old overhead projectors that focuses the light by a large parabolic mirror under the platform rather than a Fresnel lens on the platform. The heat filter and the mirror system above the projector have both been removed. There is sufficient heat focused about two feet above the projector to burn a piece of black paper in a few seconds. White paper takes longer. Why?
SUGGESTIONS: Keep hands away from focus!
REFERENCES: (PIRA 6A20.60)
EQUIPMENT: Old mirror-type overhead projector with heat filter and upper lens/mirror assembly removed, black paper.
SETUP TIME: None.
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