Two polaroids are oriented with their planes perpendicular to incident light and transmission axis making an angle 30° with each other. What fraction of incident unpolarised light is transmitted? (cos 30° = √(3)/2) (a) 57.5% (b) 17.5% (c) 27.5% (d) 37.5%

Answer: (d). First polaroid passes half the unpolarised light: I₁ = I/2. Malus's law: I₂ = I₁cos ² 30° = I/2×3/4 = 3I/8 3/8 = 37.5% So the answer is (d) 37.5%.

Two polaroids are oriented with their planes perpendicular to… | MHT CET 2025 (23 Apr, Shift 1)

Q15MHT CET 2025 · 23 APR · SHIFT 1Easy

Polarisation

Two polaroids are oriented with their planes perpendicular to incident light and transmission axis making an angle $30^\circ$ with each other. What fraction of incident unpolarised light is transmitted? $\left(\cos 30^\circ = \sqrt{3}/2\right)$

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Answer: (d)

First polaroid passes half the unpolarised light: $I_1 = \dfrac{I}{2}$ .
Malus's law: $I_2 = I_1\cos^2 30^\circ = \dfrac{I}{2}\times\dfrac{3}{4} = \dfrac{3I}{8}$
$\dfrac{3}{8} = 37.5\%$
So the answer is (d) $37.5\%$ .

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Polarisation question from MHT CET 2025 (23 Apr, Shift 1)

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