Q240: Properties of Light – Optical Isomerism – Rotation of Polarized Light
Introduction
Light corn syrup is used to rotate the plane of polarized light on the stage of an overhead projector.
A polarizing filter allows only those photons with electric fields oscillating in a single plane to pass through (plane-polarized light). This light can then pass through a parallel filter but is blocked by a perpendicular filter.
When the plane-polarized light from one filter is passed through an optically active substance such as corn syrup, the plane of the polarized light is rotated. This rotated light is partially blocked by a second filter parallel to the first but allowed to pass completely through a second filter, which has been rotated by an angle equal to the rotation of the light.
To Conduct Demonstration
- Place two polarizing filters on an overhead projector.
- Show how parallel filters allow light to pass through, while filters perpendicular to each other exclude light.
- Pour light corn syrup into a crystallizing dish. Place the dish between the two polarizing filters in the parallel position. The light passing through the corn syrup will be partially blocked due to a 25° to 30° rotation of the plane. This circular area will appear as a slightly darker area on the projection screen.
- Rotate one of the polarizing filters until the maximum amount of light passes through the corn syrup. The angle between the lines drawn on the filters is equal to the angle of rotation of the plane of polarized light after passing through the corn syrup.
Reaction Time: Leave for the rest of the class period
Safety
Do not spill corn syrup on the projector.
Acknowledgment
Stewart Strickler, Spring 1987