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Asked in GSEB Board March 2020 (old course) · Malus's law and polaroids
Given: unpolarised light of intensity I₀ falling on a single polariser.
Idea: unpolarised light has its vibrations shared equally among every direction perpendicular to the ray, so no orientation of the polaroid is special.
Resolve each wave along and across the pass axis; only the component along it gets through, contributing I₀ cos²θ for a wave at angle θ.
Averaging over all orientations, cos²θ = 1/2.
So I = (I₀)/2, whichever way the polaroid is turned.
The transmitted intensity is half that of the incident light.
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