(a) Distinguish between unpolarised light and linearly polarised light. How does one get linearly polarised light with the hel of a polaroid ?
(b) A narrow beam of unpolarised light of intensity `I_(0)` is incident on a polaroid `P_(1)`. The light transmitted by it is then incident on a second polaroid `P_(2)` with its pass axis making angle of `60^(@)` relative to the pass axis of `P_(1)`. find the intensity of the light transmitted by `P_(2)`.

Explanation

(b) When a narrow beam of unpolarised light of intensity `I_(0)` is incident on a polarised `P_(1)`, the transmitted light is plane polarised light whose intensity is `I_(1)=(I_(0))/(2)`.
When the plane polarised light is incident on a second polaroid `P_(2)` with its pass axis making an angle of `theta=60^(@)` relative to the pass axis of `P_(1)`, then intensity `I_(2)` of emergent light from `P_(2)` is
`I_(2)=I_(1)cos^(2)theta=((I_(0))/(2))xx(cos60^(@))^(2)=(I_(0))/(2)xx((1)/(2))^(2)=(I_(0))/(8)`.