Question

As shown in the figure, three identical polaroids $P_1,P_2$ and $P_3$ are placed one after another. The pass axis of $P_2$ and $P_3$ are inclined at angle of $60^{\circ }$ and $90^{\circ }$ with respect to axis of $P_1$. The source $S$ has an intensity of $256\frac{W}{m^2}$. The intensity of light at point $O$ is ____ $\frac{W}{m^2}$

Answer 1

Answer: 24

By first polaroid $P_1$ intensity will be halved then $P_2$ and $P_3$ will make intensity ${\cos }^2\left(60^{\circ }\right)$ and ${\cos }^2\left(30^{\circ }\right)$ times respectively.
Intensity out $=\frac{256}{2}\times \frac{1}{4}\times {\left(\frac{\sqrt{3}}{2}\right)}^2=\frac{256\times 3}{2\times 4\times 4}=24$