A concave mirror of focal length f in air is dipped in a liquid of refractive index . Its focal length in the liquid will be:
- f
- f
- f
- f( -1)
Answer
(2) f
Solution
A mirror works by reflection only, so its focal length depends on the geometry alone: f= R2.
[figure]
A ray parallel to the axis is reflected through the same F in air and in the liquid; the medium does not enter the law of reflection.
f'=f
Answer: (2)