7A50.10  

See also 6A44.42

Disclaimer:

Reprinted by permission of Dick Berg, University of Maryland, for use on this website.

The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources.

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Press the light pipes together with a C-clamp where the light beam bounces off the edge in one and the beam will be directed into the other pipe.  Or point the laser into one of the lenses when it is set at an angle and show the total internal reflection. Smear a little glycerin or watch oil onto the flat edge of the other lens. Bring this lens up to the other lens to form a full circle and the laser ray will jump the boundary layers of the two lenses and become a straight line.  You can also use glycerin with the light pipes if you want to dispense with the C-clamps.   Since we are using very crude optics and methods this is obviously not a perfect demonstration but it will still get the point across in a dramatic fashion. 

NOTE:  The watch oil that we have is fairly old and as it breaks down has a fairly unpleasant odor.  Glycerin is more environmentally friendly.