PURPOSE: To demonstrate explicitly that the angle of rotation of polarized light in an optically active medium is a function of wavelength.

DESCRIPTION: The prism spectrum part of the experiment consists of a bright point source with condenser lens and iris, a 20 cm focal length cylindrical convex lens which focuses light onto a slit, and a 20 cm focal length spherical lens which focuses the light passing through a prism onto a distant screen. After the spectrum is aligned, the optical activity arrangement, consisting of a uniform plastic cylinder of Karo syrup between two rotatable polaroids, can be positioned between the cylindrical lens and the slit, as seen in the photograph. As either polaroid is rotated a dark band moves through the spectrum, because the polaroid absorbs the color/wavelength that has rotated by that angle.

The color of the light passing through the polaroid/Karo syrup system is a series of negative colors: white minus the color removed by the polaroids. The spectra are shown below (left to right): white light, cyan (minus red), magenta (minus green), and yellow (minus blue) respectively.

SUGGESTIONS:

REFERENCES: (PIRA unknown.)

EQUIPMENT: Bright point source with condenser lens and iris, 20cm focal length cylindrical convex lens, rotating polaroid, plastic cylinder of Karo syrup, rotating polaroid, slit, 20cm focal length spherical convex lens, and equilateral prism.

SETUP TIME: 10 min.