A concave mirror of focal length f in air is dipped in a liquid of refractive index $\mathrm{\mu }$. Its focal length in the liquid will be :

The focal length of a concave mirror depends only on its radius of curvature and is given by the mirror formula:

$$f = \frac{R}{2}$$

where $R$ is the radius of curvature of the mirror.

Effect of Changing Medium

The focal length of a mirror does not depend on the refractive index of the surrounding medium.

Unlike lenses, mirrors reflect light rather than refract it.

The mirror equation remains unchanged, as reflection follows the laws of reflection, which are independent of the refractive index.

Final Answer

$$f' = f$$

Thus, the focal length of the concave mirror remains the same in the liquid, i.e., $f' = f$ regardless of refractive index.