Prism, Dispersion & Scattering question from MHT CET 2025 (26 Apr, Shift 1)

Answer: (b)

1. Normal incidence: $r_1 = 0$, so $r_2 = A$ and (small angles) $e = \mu A$. Deviation $\delta = e - A = (\mu - 1)A = 1.15^\circ$.
2. Reflected ray at the second face meets the first face at angle $2A$ inside, so it emerges at $2\mu A$ to the normal, which is the incident ray direction: $2\mu A = 6.3^\circ \Rightarrow \mu A = 3.15^\circ$.
3. $A = \mu A - (\mu - 1)A = 3.15^\circ - 1.15^\circ = 2^\circ$
4. $\mu = \frac{3.15}{2} = 1.575$, so the answer is (b).