When unpolarized light passes through a single ideal polarizer, the transmitted intensity is:
AThe original intensity $I_0$
B$I_0/2$
CZero
D$2 I_0$
Answer & Solution
Correct answer: B. $I_0/2$
Averaging $\cos^2\phi$ over all incident orientations gives $\langle\cos^2\phi\rangle = 1/2$. So unpolarized light loses half its intensity at the first polarizer; the transmitted beam is plane-polarized.
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