Ray Optics — Medium JEE physics MCQ
**[JEE Mains 2026]** The refractive index of a prism with angle A = 45° is √2. What should be the angle of incidence for a light ray such that the emerging ray grazes out of the other surface?
- A. 30°
- B. 45°
- C. 60°
- D. 90°
Solution
For grazing emergence, the angle of refraction at the second face is 90°.
At the second surface: sin r₂ = 1/μ = 1/√2, so r₂ = 45°.
For a prism: r₁ + r₂ = A, so r₁ = 45° - 45° = 0°.
At the first surface: sin i = μ sin r₁ = √2 × sin 0° = 0.
This means the light enters normal to the first face, so i = 90° for grazing incidence at first face.