Rotating Rainbows
Description: Karo syrup and water are placed on the overhead projector between crossed polarizers. As the upper polarizer is rotated over the Karo syrup and the lower polarizer, the relative angle between the plane polarizer orientation changes, thereby allowing specific wavelength ranges of color to pass through the polarizers from the white light emitted by the overhead projector lamp. This effect is seen when the liquid placed in the beaker between the polarizers has a structure which rotates polarized light. This kind of molecule is called optically active. Water is not an optically active molecule so changing the relative angle between the polarizer planes does not affect the properties of the light that passes through it.
Source: Journal of Chemical Education
Year: 1999 Vol: 76 Page: 1233 – 1236
Keywords: Isomers, Stereoisomers
Rating: 
Hazard: Low
- Electric shock hazard
- Breakage hazard
Effectiveness: Good
- Results are clearly observable without guidance
- Good connection from demo to course material
- Low failure rate
- Time to results is low
- Good effects are seen by audience
Difficulty: Low
- Simple procedures
- Simple manipulations for most to perform
- Use of glass surfaces handle with care
Safety Precautions:
- Eye protection required
- Use of UL approved three-prong plug and outlet required
Class: Organic Chemistry, Molecular Structure
Division: General, Organic Chemistry
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