Explain Malus law and write it.

Explanation

If the pass-axis of `P_(2)` makes an angle `theta` with the pass-axis of `P_(1)` then `vecE` vectors `(E_(0))` emerging from `P_(2)` makes an angle `theta` with pass axis of polaroid `P_(1)` which is shown in the figure.
By taking two component of vector `E_(0)` of plane polarized light,
(1) `E_(0)costheta` which is parallel to pass-axis of analyser `P_(1)`.
`E_(0)sintheta` which is perpendicular to pass-axis of analyser `P_(1)`.

Component `E_(0)costheta` passes through `P_(1)` while component `E_(0)sintheta` is perpendicular to pass-axis of `P_(1)` so it is absorbed.
Now intensity of light is proportional to square of amplitude intensity of light incident on analyser is `I_(0)propE_(0)^(2)` and intensity of light emerging from analyser is `Iprop(E_(0)costheta)^(2)`.
Hence, intensity of light emerging from analyser,
`(I)/(I_(0))=(E_(0)^(2)cos^(2)theta)/(E_(theta^(2)))=cos^(2)theta`
`:.I=I_(0)cos^(2)theta`
This is known as Malus law.