A glass rod having square cross-section is bent into the shape as shown in the figure. The radius of the inner semi-circle is R and width of the rod is d. The minimum value of so that the light that enters at A will emerge at B. Refractive index of glass is
0.25
0.5
0.75
0.8
Consider the figure. If smallest angle of incidence is greater than critical angle then all light will emerge out at
.
From figure,