A concave mirror of focal length 10cm in air is put into a beaker containing a liquid up to 7.5cm. Refractive index of the liquid is 1.2. What is the focal length of the mirror inside the beaker?
The Attempt at a Solution
I tried proportion method:
Depth Focal length
6.25cm(Apparent depth) 8.33cm
But I'm not convinced that this method is a legal operation. Any other way I could find the new f for the mirror?