JEE Main · 2026 · 22 Jan 2026 · Shift 1 · Geometrical Optics

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 ____ .

Answer: (A)

Solution

For the equilateral prism

A = 6 0^{\circ}

. Since the emergent ray grazes the second face, there

e = 9 0^{\circ}

, and Snell's law gives

2 sin r_{2} = sin 9 0^{\circ}

, so

sin r_{2} = \frac{1}{2}

and

r_{2} = 4 5^{\circ}

. Using

r_{1} + r_{2} = A

, the angle of refraction at the incident face is

r_{1} = 6 0^{\circ} - 4 5^{\circ} = 1 5^{\circ} .

JEE Main · 2026 · 22 Jan 2026 · Shift 1 · Single correct option