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MHT CET202520 Apr 2025Evening ShiftPhysicsWave OpticsActual

Four polaroids are placed such that the optic axis of each is inclined at an angle of 30^ with 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 [ 30= 3 / 2]

Options

  1. A9 I ₀ 32
  2. B27 I ₀ 128
  3. C35 I ₀ 128
  4. D27 I ₀ 32

Correct answer

B. 27 I ₀ 128

Step-by-step solution

Unpolarized light of intensity I₀ passes through the first polarizer, reducing the intensity by half: I₁ = I₀ 2 . The second polarizer is oriented at 30^ to the first. Applying Malus's Law: I₂ = I₁ ^2 30^ = I₀ 2 ( 3 2 )^2 = 3I₀ 8 . Each subsequent polarizer is rotated an additional 30^ from the previous one, multiplying by ^2 30^ = 3 4 each time. After three such rotations: I₄ = I₀ 2 ( 3 4 )^3 = 27I₀ 128 . The final intensity is B .

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