Locate two polarizing filters. (Your physics instructor is probably your best source. Most sunglasses are not polarizers.)
a. View the blue sky through one polarizer while rotating the polarizer around your line of sight. What changes in intensity do you observe?
b. Place one polarizer on top of the other and rotate one of them. When the polarizers are crossed (axes at 90°), no light should get through. How does the transmitted light vary as you rotate the second polarizer?

c. Place various plastic items (rulers, protractors, plastic spectacle lenses, etc.) between crossed polarizers. Describe the patterns that you observe.