Q. 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:
A) $\mu f$
B) $f$
C) $\frac f{(\mu-1)}$
D) $\frac f\mu$
Explanation
[Solution by Dr. Abubacker] For a mirror $f=\frac R2$ depends only on the geometry (reflection), not on the surrounding medium, so the focal length stays $f$. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.