Ray Optics

JEE Main level, single correct, medium

272 of 295

Question 272 of 295

A light ray is incident perpendicular to one face of a 90∘90^{\circ} prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45∘45^{\circ}, we conclude that the refractive index nn

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Answer: (B) n>2\mathrm{n}\gt \sqrt{2}

Angle of incidence i>C\mathrm{i}\gt \mathrm{C} for total internal reflection. Here i=45∘\mathrm{i}=45^{\circ} inside the medium.
∴45∘>sin⁡−1(1/n)⇒n>2.\begin{aligned} & \therefore 45^{\circ}>\sin ^{-1}(1 / n) \\ & \Rightarrow n>\sqrt{ } 2 . \end{aligned}

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