A rod made of glass, refractive index
1.5 and of square cross section, is bent into the shape shown in figure. A parallel beam of light falls normally on the plane flat surface
A. Referring to the diagram,
d is the width of a side and
R is the radius of inner semicircle. Find the maximum value of ratio
dR so that all light entering the glass through surface
A emerges from the glass through surface
B.