Purpose: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, as seen in the image above left. 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. Click on the picture above right to watch a video of this happening. White paper takes longer. Why?