Question

Unpolarised light of intensity I passes through an ideal polarizer A. Another identical polarizer B is placed behind A. The intensity of light beyond B is found to be $\frac{1}{2}$. Now another identical polarizer C is placed between A and B. The intensity beyond B is now found to be $\frac{1}{8}$. The angle between polarizer A and C is?

• A. ${45}^o$
• B. ${60}^o$
• C. $0^o$
• D. ${30}^o$

Answer 1

The correct option is A ${45}^o$

let initial intensity be $I_0$.

intensity of the beam after passing through A is $I_1=\frac{I_0}{2}$

given that intensity after C is $\frac{I_0}{2}$.

then angle between A and C is zero.

A polariser B is introduced between A and C then by Molus law

after B $I_b=\frac{I_0}{2}co{s}^2\theta$

and after C $I_c=I_{b}co{s}^2\theta$

so given $I_c=\frac{I_0}{8}$

from here solving all the three equations $\frac{I_0}{8}=\frac{I_0}{2}co{s}^4\theta$

$\theta =45$