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Two polaroid sheets are placed one over the other with their transmission axes inclined at 30 deg to each other. Unpolarised light of intensity I0 is incident. Find the ratio of the incident unpolarised intensity to the emergent (polarised) intensity.

1. 1/2
2. 3/4
3. 8/3
4. 3/1

Correct answer: 8/3

Solution

After the first polaroid, intensity = I0/2. After the second, by Malus's law, I = (I0/2) cos²(30 deg) = (I0/2)(3/4) = 3 I0/8. The ratio incident/emergent = I0/(3 I0/8) = 8/3.

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