Question

Three identical polaroid sheets P₁, P₂ and P₃ are oriented so that the pass axis of P₂ and P₃ are inclined at angles of 60° and 90° respectively with the pass axis of P₁. A monochromatic source S of unpolarised light of intensity I₀ is kept in front of the polaroid sheet P₁ as shown in the figure. Determine the intensities of light as observed by the observer at O, when polaroid P₃ is rotated with respect to P₂ at angles θ = 30° and 60°.

Answer 1

The ray of light passing through polaroid P₁ will have intensity reduced by half.'

`I_1=I_0/2`

Now, the polaroid P₂ is oriented at an angle 60° with respect to _P1.
Therefore_, the intensity is

`I_2=I_1cos^2 60=I_0/2xx1/4=I_0/8`

Now, the polaroid P₃ is originally oriented at an angle 90 − 60 = 30°. Hence, when P₃ is rotated by 30°, the angle between P₂ and P₃ is 60°. Therefore, the intensity is

`I_3=I_2cos^2 60=I_0/8cos^2 60=I_0/8xx1/4=I+0/32`

Similarly, when P₃ is rotated by 60°, the angle between P₂ and P₃ is 90°.

Therefore, the intensity is `I_3=I_2cos^2 90=I_0/8xx0xx0`