A source of light is placed in front of a screen.Intensity of light on the screen is $I$. Two polaro

Question

A source of light is placed in front of a screen.Intensity of light on the screen is $I$. Two polaroids $P_{1}$ and $P_{2}$ are so placed in between the source of light and screen that the intensity of light on screen is $I / 2 . P_{2}$ should be rotated by a angle of _______ (degrees) so that intensity of light on the screen becomes $\frac{3 I}{8}$.

Professor PC Thomas Classes · Answer

(30) : Let $P_{2}$ is rotated by angle $	heta$.\ By the law of Malus, $I=I_{0} \cos ^{2} 	heta$\ $\frac{3 I}{8}=\frac{I_{0}}{2} \cos ^{2} 	heta$\ $\Rightarrow \cos ^{2} 	heta=\frac{3}{4} \Rightarrow \cos 	heta=\frac{\sqrt{3}}{2} \Rightarrow 	heta=30^{\circ}$\