Question

When a polaroid sheet is rotated between two crossed polaroids, the intensity of the transmitted will be maximum, when angle `theta` between pass axes is
A. `pi/2`
B. `(3pi)/4`
C. `pi/4`
D. `(2pi)/3`

Answer 1

Correct Answer - C
Let `I_(0)` be the intensity of polarised light after passing through the first polariser `P_(1)`. Then, the intensity of light after passing through second polariser `P_(2)` will be,
`I=I_(0)cos^(2)theta`
where, `theta` is the angle between pass axes of `P_(1) and P_(2)`. Since, `P_(1) and P_(3)` are crossed, the angle between the pass axes of `P_(2) and P_(3)` will be `(pi/2-theta)`. Hence, the intensity of light emerging from `P_(2)` will be
`I=I_(0)cos^(2)thetacos^(2)(pi/2-theta)`
`or" "I=I_(0)cos^(2)thetasin^(2)theta=((I_(0))/4)sin^(2)2theta`
Hence, transmitted intensity will be maximum, when`theta=pi/4`.