Concepts

Birefringence, polarization

Overview

A cellophane sheet between crossed polarizers produces beautiful coloured patterns due to the birefringence of the cellophane. Variations in the pattern occur due to variations in the thickness of the sheet, stresses due to crinkles, and the wavelength dependence of the birefringence.

Details

Equipment

• [2] Polaroid sheet
• [1] Cellophane sheet
• [1] Glass plate taped with cellophane
• [1] Cellophane tape
• [1] Overhead projector

Script

1. Turn off the lights.
2. Turn on the projector.
3. Put the cellophane sheet on the overhead projector as a control experiment.
4. Put the cellophane sheet between crossed polaroids on the projector.
5. Rotate the top polaroid for a minor light show.
6. Place the glass plate between the polaroids.
7. Remove the glass plate and add some tape to the glass.
8. Put the glass plate back between the polaroids.
9. Turn off the projector.
10. Turn on the lights.

Additional Resources