JEE Main 2026 Apr 6 Shift 1, Physics Q22: Wave Optics

JEE Main2026Apr 6, Shift 1Physics

An unpolarized light of intensity $I_{0}$ passes through polarizer and then through a certain optically active solution and finally it goes to analyser. If the angle between analyser and polariser is $0^{\circ}$ and intensity of light emerged from analyser is $\frac{3}{8} I_{0}$ , the angle of rotation of the light by the solution with respect to analyser is ________ degrees.

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Solution

After the polariser the intensity is $I_{0} /2$ and the light is linearly polarised. The optically active solution rotates the polarisation by angle $θ$ . The analyser axis is aligned with the polariser ( $0^{\circ}$ between them), so the angle between the analyser axis and the now-rotated polarisation is $θ$ .

Malus's law: $I = \frac{I _{0}}{2} cos^{2} θ = \frac{3 I _{0}}{8}$ .

$cos^{2} θ = \frac{3}{4} \Rightarrow cos θ = \frac{3}{2} \Rightarrow θ = 3 0^{\circ}$ .

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