Four polaroids are placed such that the optic axis of each is inclined at an angle of 30° the optic axis of the preceding one. If unpolarised light of intensity ' I₀ ' falls on the first polaroid, the intensity of light transmitted from the fourth polaroid is [cos 30° = √(3)/2] (a) (9I₀)/(32) (b) (27I₀)/(128) (c) (35I₀)/(128) (d) (27I₀)/(32)

Answer: (b). First polaroid passes I₀/2; each of the next three reduces by cos ² 30° = 3/4. I = I₀/2(3/4)³ = I₀/2·27/64 So the answer is (b) (27I₀)/(128).

Four polaroids are placed such that the optic axis of each is… | MHT CET 2025 (20 Apr, Shift 2)

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Polarisation

Four polaroids are placed such that the optic axis of each is inclined at an angle of $30^\circ$ the optic axis of the preceding one. If unpolarised light of intensity ' $I_0$ ' falls on the first polaroid, the intensity of light transmitted from the fourth polaroid is $\left[\cos 30^\circ = \frac{\sqrt{3}}{2}\right]$

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Answer: (b)

First polaroid passes $I_0/2$ ; each of the next three reduces by $\cos^2 30^\circ = \frac{3}{4}$ .
$I = \frac{I_0}{2}\left(\frac{3}{4}\right)^3 = \frac{I_0}{2}\cdot\frac{27}{64}$
So the answer is (b) $\frac{27I_0}{128}$ .

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Polarisation question from MHT CET 2025 (20 Apr, Shift 2)

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