PURPOSE: To illustrate some fundamental properties of sound and light.

DESCRIPTION: The following sequence provides good introductory examples of the behavior of light:

(1) Have smoke in the bell jar with the laser beam going in but terminated by a felt pad (on the right side of the jar) and the bell on.

(2) Ask "In what does light travel?" Then turn on the pump. The sound dies out and the light path seemingly dies out also.

(3) Remove the felt to show that the light didn't stop after all. Therefore light travels in a vacuum.

(4) Pull the cap off the water tank; the light follows the water path and one can claim to be collecting the light in the glass pan into which the water shoots. Dip out some water with a beaker to show that the water is red (colored with food coloring ).

Discussion of total internal reflection can occur at this point or later in the course.



EQUIPMENT: BELL IN VACUUM demonstration, laser, smoke source (cigarettes), red food coloring, nipple container on lab jack, clear glass pie pan, beaker.

SETUP TIME: 20 min.

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