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Asked in GSEB Board March 2023 · Malus's law and polaroids
Given: unpolarised light of intensity I₁ falls on a single polaroid and light of intensity I₂ comes out.
Idea: unpolarised light contains vibrations in every direction perpendicular to the ray, with no direction preferred, and averaging Malus' law over all of them gives a factor cos²θ=1/2.
The polaroid passes only the component along its own axis.
I₂=(I₁)/2.
I₁=2I₂.
The same half is lost whatever way the polaroid is turned -- rotating it changes the direction of polarisation of the emerging beam, not its brightness.
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