A ray enters a glass hemisphere as shown in the figure. What must be the radius 
of the hemisphere and the distance 
, from the centre of the hemisphere, of the point on the surface of the hemisphere through which the ray penetrates so that the ray is completely reflected such that both the incident and reflected rays are parallel to each other and the distance between them is 
? The refractive index of glass is 1.51.
Double light reflection in a glass hemisphere
