Question

Using concepts of optics, explain why sometimes you can not see a rainbow with polarized sunglasses

Answer 1

During the tempering process, the glass is heated and then rapidly cooled to room temperature. The surface of the glass cools much faster than the center of the glass and contracts, causing compressive stresses, while the center of the glass expands because of its temperature, producing tensile stresses.

Stress on optically clear materials often produces birefringence, which basically means that the material changes the polarization of the light.

You can also observe stressed birefringence in objects such as plastic utensils or cups. If you put on polarized lenses and hold a plastic cup in front of a computer screen, you should be able to see the same rainbow pattern you observe in a car. This method is known as photoelasticity, and scientists and structural engineers use it to determine the stress distribution in a material.

The reason you don’t see any rainbows or patterns in a windshield is that windshields are made of laminated safety glass, not tempered glass.