Concepts

Stress-induced birefringence

Overview

Plastic objects between crossed polarizers produce colour variations in the plastic, which are caused by stress-induced birefringence. There is a set of plastic pincers to show the effect of stress on the plastic.

Details

Equipment

• [2] Polaroid sheet
• [1] Plastic French curve
• [1] Plastic pincer 
• [1] Overhead projector

Script

1. Turn off the lights.
2. Turn on the projector.
3. Put the French curve and pincer on the projector as a control experiment.
4. Place the French curve between the crossed polarizers on the projector.
5. Place the plastic pincer between the crossed polarizers.
6. Pinch and unpinch the pincer.

Additional Resources