A right prism is to be made by selecting a proper material and the angles A and B (BA), as shown in figure (18-W5a). It is desired that a ray of light incident normally on AB emerges parallel to the incident direction after two internal reflections. (a) What should be the minimum refractive index u for this to be possible ? (b) For u = 5/3, is it possible to achieve this with the angle A equal to 60 degrees?