JEE Main 2025 Jan 23 Shift 2, Physics Q19: Reflection at Plane and Spherical Surfaces

JEE Main2025Jan 23, Shift 2Physics

A concave mirror of focal length $f$ in air is dipped in a liquid of refractive index $μ$ . Its focal length in the liquid will be :

Solution

For a spherical mirror, $f = \frac{R}{2}$ , which depends only on the geometry of the mirror surface, not on the surrounding medium.

Reflection laws are unchanged by the medium (unlike refraction at a lens), so the focal length stays $f$ when the mirror is immersed.

Concept behind this question

Concept-wise practice with instant solutions on Fundamenthol.