What is a polaroid ? Write any two applications.

Polaroids are used as a filter in the photographic camera. They are used in the production and analysis of plane-polarised light. They are used to improve colour contrast in old oil paintings. They are used in calculators, watches, monitors of laptops which have LCD screens.

When one can notice the phenomenon of diffraction of light?

More specifically when applied to light, diffraction of light occurs when a light wave passes by a corner or through an opening or slit that is physically the approximate size of, or even smaller than that light's wavelength.