Definitions [1]
What is a Polaroid?
A Polaroid is a material which polarises light. The phenomenon of selective absorption is made use of in the construction of polariods. There are different types of polaroids.
A Polaroid consists of micro crystals of herapathite (an iodosulphate of quinine). Each crystal is a doubly refracting medium, which absorbs the ordinary ray and transmits only the extra ordinary ray. The modern polaroid consists of a large number of ultra microscopic crystals of herapathite embedded with their optic axes, parallel, in a matrix of nitro - cellulose.
Recently, new types of polariod are prepared in which thin film of polyvinyl alcohol is used. These are colourless crystals which transmit more light, and give better polarisation.
Theorems and Laws [1]
State law of Malus.
It states that when a completely plane polarised light beam is incident on an analyzer, the intensity of the emergent light varies as the square of the cosine of the angle between the plane of transmission of the analyzer and the polarizer.
I = I0cos2θ
