Question 176 of 191

A source of light is placed in front of a screen. The 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 the screen is $\dfrac{I}{2}$. Then the ${P}_{2}$, should be rotated by an angle of (degrees) so that the intensity of light on the screen becomes $\dfrac{3I}{8}$.

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Answer: 30

Recall the law of Malus ${I}^{'}=\dfrac{I}{2}{\cos }^{2}\theta$
Here $\theta$ is the angle between two polaroids,
$\Rightarrow \dfrac{3I}{8}=\dfrac{I}{2}{\cos }^{2}\theta$$\Rightarrow \theta =30^{\circ}$.