PURPOSE: To demonstrate total internal reflection of a laser beam in a water jet.

DESCRIPTION: The upper vessel is filled with water with a trace of powdered creamer to make the laser beam more visible. Align the laser beam so that it is centered in the nipple through which the water leaves the container. Several internal reflections of the laser beam are clearly visible until the water flow becomes so slow that there is no internal reflection. The overall effect can be easily seen throughout the lecture hall; a color TV camera with zoom lens is available for better detailed visibility in the lecture halls.

A great gag is as follows: Put a little red dye into the receptacle container before doing the experiment. After the experiment is complete, display a glass beaker of the water from the receptacle, which is clearly a pink color. Point out that some of the laser light remains in the water.



EQUIPMENT: Pre-assembled laser waterfall setup with laser, water, red food coloring and glass beaker.

SETUP TIME: 5 min.

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