(i) The rings (shaded and non-shaded) are known as the Fresnel zones. The distance from T to a point on the circle to R is longer by some multiple of an half wavelength than the main beam. This difference in length is the cause of the Fresnel interference phenomenon.
(ii) Uses of Polaroid :
1. Polaroids are used in the laboratory to produce and analyse plane polarised light.
2. Polaroids are widely used as polarizing sun glasses.
3. They are used to eliminate the head light glare in motor cars.
