Q 12-09-043JEE MainJEE Main 2026 (5 Apr, Shift 1)Medium
A ray of light passing through an equilateral prism is having velocity $2.12 \times 10^8$ m/s in the prism material, then the minimum angle of deviation is ______ degrees.
Answer: (B) $30$
Concept. $\mu=\dfrac cv$, then invert the minimum-deviation formula.
Step 1. Index. $\dfrac{3\times10^8}{2.12\times10^8}=1.414=\sqrt2$.
Step 2. Deviation. $\sin\dfrac{60^\circ+\delta}{2}=\sqrt2\sin30^\circ=\dfrac{1}{\sqrt2}\Rightarrow\dfrac{60^\circ+\delta}{2}=45^\circ$, $\delta=30^\circ$.
Answer. Option B.
Solution by Sreeraj P, M.Sc Physics
