Unpolarized light of intensity I₀ passes successively through four ideal polaroids whose transmission axes are at 0°, 30°, 60° and 90°, respectively. What is the final transmitted intensity?
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Question

Unpolarized light of intensity I₀ passes successively through four ideal polaroids whose transmission axes are at 0°, 30°, 60° and 90°, respectively. What is the final transmitted intensity?

G1 Physics · Accepted Answer

After the first polarizer, I₁ = I₀ ÷ 2. Each successive pair of axes differs by 30°. Therefore, I(final) = (I₀ ÷ 2)(cos²30°)³. Since cos²30° = 3 ÷ 4, we get I(final) = (I₀ ÷ 2)(3 ÷ 4)³ = (I₀ ÷ 2)(27 ÷ 64) = 27I₀ ÷ 128. Correct option: A.