What must be 'n' of a sphere surrounded by water so that the parallel rays that affect one of its faces converge on the second vertex of the sphere?

The refractive index of the sphere is 2.66

Solution:

The refractive index, and since the sphere is surrounded by water.

Therefore, according to the question, the parallel rays that affect one of the faces of the sphere converges on the second vortex:

Thus the image distance from the pole  of surface 1, v' = 2R

where

R = Radius of the sphere

Now, using the eqn:

Since, v is taken as infinite

n = 2.66

answer; (arch); good luck