A concave spherical mirror with a radius of curvature of `0.2 m` is filled with water. What is the focal length of this system? Refractive index of water is `4//3.`

Answer

A, C

Explanation

The system behaves like a mirror of
focal length given by
`1/F=(2(n_2//n_1))/(R_2)-(2(n_2//n_1))/(R_1)`
Substituting the values with proper
sign.
`1/F=(2xx4//3)/(-20) (:' R_1=oo)`
or `F=-7.5 cm`
i.e. system behaves as a concave mirror of focal
length `7.5 cm`