Unpolarised light falls first on a polariser (P) and then on an analyser (A). If the intensity of the light transmitted by the analyser is 1/8 of the incident unpolarised intensity, what is the angle between the axes of P and A?

Question

Accepted Answer

(4) 60°. Given: unpolarised light of intensity I₀ through a polariser and then an analyser, with the final intensity I = (I₀)/8. Idea: a polariser passes half of unpolarised light whatever its orientation; the analyser then applies Malus's law to that already polarised beam. After the polariser, I₁ = (I₀)/2. After the analyser, I = I₁ cos²θ = (I₀)/2 cos²θ. Setting (I₀)/2 cos²θ = (I₀)/8 gives cos²θ = 1/4, so cos θ = 1/2. The angle between the axes of P and A is 60°.

Unpolarised light falls first on a polariser (P) and then on an analyser (A). If the intensity of the light transmitted by the analyser is 1/8 of the incident unpolarised intensity, what is the angle between the axes of P and A?

Step-by-step solution

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