An example of how every day products can be optically active.
TeachableTopics:
- Polarization
- Birefringence
- Chiral molecules
- Dispersion of light
Theory:
Many substances can be optically active. Regular household corn syrup, for example, is a naturally birefringent substance. This means that if polarized light is passed through it, it will remain polarized but its axis of polarization will rotate depending on the path length the light has traveled.
Corn syrup is an optically active medium made of helical sugar molecules which allows the corn syrup to exhibit birefringent properties. Birefringence occurs in substances which have physical properties that cause the substance to have more than one index of refraction. The various wavelengths of light produced when white light is sent through the syrup can then be viewed individually with a polarizer. By placing a polarizer underneath a beaker of corn syrup and another above, rotating the top polarizer will allow one to view all of the various wavelengths rotated through different degrees.
Apparatus:
- Small beaker
- Approximately one cup of corn starch
- Two mountable polarizers and mounts
- Weighted stand
- Two double-sided stand clamps
- Cardboard with a circular hole cut in it to have a more direct path of light
- Overhead projector and screen (optional)
Procedure:
- Place the overhead projector in front of the screen.
- Attach the polarizers to their mounts and mount both to the weighted stand using the double sided stand clamps. Mount one directly above the other, both parallel to the floor. Make sure the polarizers are far enough apart that the beaker can fit easily in between and that they are high enough that the overhead projector can be placed underneath them.
- Place the stand with the polarizers attached beside the projector so that the polarizers are above the light source.
- Pour the corn starch into the beaker and place it on top of the lower polarizer.
- Turn the projector on and rotate the top polarizer through its full range to see all the wavelengths present in the white light
