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By Malus's law, if plane-polarised light of intensity I_0 passes through a polariser oriented at 60° to the polarisation direction, the transmitted intensity is:
A$I_0$ (full transmission, no change)
B$I_0 / 2$ (half intensity, the typical case)
C$I_0 / 3$ (one third, by special rule)
D$I_0 / 4$ (since $\cos^2 60° = 1/4$)
Answer & Solution
Correct answer: D. $I_0 / 4$ (since $\cos^2 60° = 1/4$)
Malus's law: I = I_0 cos²(θ). At θ = 60°, cos 60° = 0.5, cos² 60° = 0.25 = 1/4. So I = I_0/4.
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