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JEE Main 2018 · Polarisation

Polarisation question from JEE Main 2018

Q55JEE Main 2018Medium

Polarisation

Unpolarized light of intensity I passes through an ideal polarizer A. Another identical polarizer B is placed behind A. The intensity of light beyond B is found to be I/2. Now another identical polarizer C is placed between A and B. The intensity beyond B is now found to be I/8. The angle between polarizer A and C is:

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Answer: (c)

Output $I/2$ means A and B are parallel, so C makes the same angle $\theta$ with both.
$\frac{I}{2}\cos^4\theta = \frac{I}{8} \Rightarrow \cos^4\theta = \frac{1}{4} \Rightarrow \cos^2\theta = \frac{1}{2}$
So the answer is (c) $45^\circ$ .

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