A parallel incident beam falls on a solid glass sphere at normal incidenc. Prove that the distance of the fianll image after two refractions is at a distance `(2-mu)//2(mu-1)a` from the outer edge of the sphere. Refractive index of the sphere is `mu` and radius of the sphere is a.

Explanation

`(mu)/(y_(1))-(1)/(oo)=(mu-1)/(a)`
`(1)/(y_(2))-(mu)/((y_(1)-2a))=(1-mu)/(-a)`
Solving (i) and (ii), we get
`y_(2)=((2-mu)a)/(2(mu-1))`