The exit surface of a prism with refractive index n is coated with a material having refractive index n/2. When this prism is set for minimum angle of deviation, it exactly meets the condition of critical angle. The prism angle is ______. (a) 60° (b) 30° (c) 15° (d) 45°

Answer: (a). At minimum deviation r₁ = r₂ = A/2. Critical condition at exit face: n /2 = n/2sin 90° ⇒ /2 = 1/2. A/2 = 30° ⇒ A = 60° So the answer is (a) 60°.

The exit surface of a prism with refractive index n is coated with a… | JEE Main 2026 (24 Jan, Shift 1)

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Prism, Dispersion & Scattering

The exit surface of a prism with refractive index $n$ is coated with a material having refractive index $\frac{n}{2}$ . When this prism is set for minimum angle of deviation, it exactly meets the condition of critical angle. The prism angle is ______.

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Answer: (a)

At minimum deviation $r_1 = r_2 = \dfrac{A}{2}$ .
Critical condition at exit face: $n \sin\dfrac{A}{2} = \dfrac{n}{2}\sin 90^\circ \Rightarrow \sin\dfrac{A}{2} = \dfrac{1}{2}$ .
$\dfrac{A}{2} = 30^\circ \Rightarrow A = 60^\circ$
So the answer is (a) $60^\circ$ .

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