A point object 'O' is kept in a medium of refractive index n1 in front of a convex spherical surface of radius of curvature R which separates the second medium of refractive index n2 from the first one, as shown in the figure.
Draw the ray diagram showing the image formation and deduce the relationship between the object distance and the image distance in terms of n1, n2 and R.
Ray diagram showing the image formation is given below:
The rays are incident from medium of refractive index n1 to another medium of refractive index n2.
NM is taken to be nearly equal to the length of the perpendicular from the point N on the principal axis.
We can have approximation for small angles. We get, 
b)
When the image formed is virtual and n2 > n1
