JEE Main 2026 — Jan 22, Shift 1 — Physics solution

JEE Main2026Jan 22, Shift 1Physics

Consider an equilateral prism (refractive index $2$ ). A ray of light is incident on its one surface at a certain angle $i$ . If the emergent ray is found to graze along the other surface then the angle of refraction at the incident surface is close to _____.

A
15°
B
20°
C
40°
D
30°

Solution

For an equilateral prism, $A = 60 d e g;$ .

Grazing emergence at the second surface means the angle of emergence is 90°, so the angle of refraction at the second surface equals the critical angle: $sin r_{2} = \frac{1}{μ} = \frac{1}{2}$ , giving $r_{2} = 45 d e g;$ .

Prism geometry: $r_{1} + r_{2} = A$ , so $r_{1} = 60 d e g; - 45 d e g; = 15 d e g;$ .

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