JEE MAIN - Physics (2021 - 26th August Evening Shift - No. 19)
A source of light is placed in front of a screen. Intensity of light on the screen is I. Two Polaroids P1 and P2 are so placed in between the source of light and screen that the intensity of light on screen is I/2. P2 should be rotated by an angle of (degrees) so that the intensity of light on the screen becomes $${{3I} \over 8}$$.
Answer
30
Explanation
$$I = {{{I_0}} \over 2}{\cos ^2}\phi $$
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$${{{I_0}} \over 2}{\cos ^2}\phi = {{3I} \over 8}$$
$${\cos ^2}\phi = {3 \over 4}$$
$${\cos ^2}\phi = {{\sqrt 3 } \over 2}$$
$$ \Rightarrow \phi = 30$$
$${{{I_0}} \over 2}{\cos ^2}\phi = {{3I} \over 8}$$
$${\cos ^2}\phi = {3 \over 4}$$
$${\cos ^2}\phi = {{\sqrt 3 } \over 2}$$
$$ \Rightarrow \phi = 30$$
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