State and obtain Malus' law.

Explanation

When a beam of completely plane polarised light is passed through an analyser, the intensity I of the transmitted light varies directly as the square of the angle `theta` between the transmission directions of polariser and analyser. This is known as Malus law. Let `I_(0)` be the intensity and a be the amplitude of the electric vector transmitted by the polariser. Only the component `a cos theta` parallel to the axis of transmission of the analyser will be transmitted by the analyser. The intensity of light transmitted from the analyser is proportional to the square of the component of the amplitude transmitted by the analyser.
`I alpha (acos theta)^(2)`
`I = k(a cos theta)^(2)`
`I = ka^(2)cos^(2)theta`
`I = I_(0)cos^(2)theta`
Where k is the constant of proportionality. `I_(0) = ka^(2)` is the maximum intensity of light transmitted from the analyser.