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: (a) μ f (b) f (c) f/μ (d) (f)/((μ-1))

Answer: (b). For a mirror f = R/2, which depends only on the geometry of the surface. Reflection does not depend on the refractive index of the surrounding medium, so f is unchanged. So the answer is (b) f.

A concave mirror of focal length f in air is dipped in a liquid of… | JEE Main 2025 (23 Jan, Shift 2)

Q6JEE Main 2025 · 23 JAN · SHIFT 2Easy

Reflection & Mirrors

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:

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Answer: (b)

For a mirror $f = \frac{R}{2}$ , which depends only on the geometry of the surface.
Reflection does not depend on the refractive index of the surrounding medium, so $f$ is unchanged.
So the answer is (b) $f$ .

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