Q 12-09-068JEE MainJEE Main 2025 (23 Jan, Shift 2)Easy
A concave mirror of focal length $f$ in air is dipped in a liquid of refractive index $\mu$. Its focal length in the liquid will be
Answer: (B) $f$
The focal length of a mirror is $f = R/2$, fixed by its geometry alone. Reflection does not depend on the refractive index of the surrounding medium, so the focal length stays $f$.
Solution by Sreeraj P, M.Sc Physics