**Malus' law** gives the transmitted intensity through a second polarizer as:
A$I = I_0 \sin\theta$
B$I = I_0 \cos^2\theta$
C$I = I_0 \sin^2\theta$
D$I = I_0$
Answer & Solution
Correct answer: B. $I = I_0 \cos^2\theta$
When plane-polarized light (intensity $I_0$) hits a polarizer whose axis makes angle $\theta$ with its polarization, the transmitted intensity is $I_0 \cos^2\theta$. At $\theta = 0$, full intensity; at $\theta = 90°$, zero (crossed polarizers).
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