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Unpolarized light of intensity $I_0$ passes through three polarizers in succession. The axis of the second makes angle 45° with the first, and the axis of the third makes 45° with the second. The intensity after the third polarizer is:

A$I_0/8$
B$I_0/4$
C$I_0/2$
D$I_0$
Answer & Solution
Correct answer: A. $I_0/8$
$I_1 = I_0/2$ (unpolarised through P1). $I_2 = I_1 \cos^2 45° = (I_0/2)(1/2) = I_0/4$. $I_3 = I_2 \cos^2 45° = (I_0/4)(1/2) = I_0/8$.
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