Question

Light from a sodium lamp (S) passes through two polaroid sheets P₁ and P₂ as shown in fig. What will be the effect on the intensity of the light transmitted (i) by P₁ and (ii) by P₂ on rotating polaroid P₁ about the direction of propagation of light ? Justify your answer in both cases.

Answer 1

 

Let the intensity of light from sodium lamp is I₀, then the intensity transmitted through P₁ is \(\frac{I_0}{2}\) at any orientation of P₁

i.e., \(I_1 = \frac{I_0}{2}\) 

Now, let angle between P₁ and P₂ at a given orientation is \(\theta\) then by Malus' law the intensity of light transmitted through P₂ is

\(I_2 = I_1 \ cos^2 \theta\)

Therefore, if P₁ is rotated then \(\theta\) changes and hence I₂ will also change, while I₁ remains unchanged.