JEE Advanced2021PhysicsRay OpticsActual
A wide slab consisting of two media of refractive indices n 1 and n 2 is placed in air as shown in the figure. A ray of light is incident from medium n 1 to n 2 at an angle θ , where sin θ is slightly larger than 1 n 1 . Take refractive index of air as 1 . Which of the following statement(s) is (are) correct?
Options
- AThe light ray enters air if n 2 = n 1 .
- BThe light ray is finally reflected back into the medium of refractive index n 1 if n 2 < n 1 .
- CThe light ray is finally reflected back into the medium of refractive index n 1 if n 2 > n 1 .
- DThe light ray is reflected back into the medium of refractive index n 1 if n 2 = 1 .
Correct answer
B. The light ray is finally reflected back into the medium of refractive index n 1 if n 2 < n 1 .
Step-by-step solution
Option A: If n 1 = n 2 , n 1 sin θ = n 2 sin θ 1             . . . 1 and n 2 sin θ 1 = 1 × sin r           . . . 2 From (1) and (2), sin r = n 1 sin θ Now, sin θ > 1 n 1 , (given) ∴   sin r > 1 (which is not possible) and hence light will reflect back from air ,   n 2 interface Option B: If n 2 < n 1 , Snell's law at A , n 1 sin θ = n 2 sin θ 1           . . . 3 Sne