A horizontal ray of white light incident perpendicularly on the vertical face of a prism made of crown glass. The ray enters the prism, and part of the light undergoes refraction at the slanted face and emerges into the surrounding material. The rest of the light is totally internally reflected and exits through the horizontal base of the prism. The colors of light that emerge from the slanted face of the prism may be chosen by altering the index of refraction of the material surrounding the prism. Find the required index of refraction of the surrounding material so that (a) only red light and (b) all colors except violet emerge from the slanted face of the prism. Give your answers to four significant figures. Take n = 1.520 for crown glass for red light, and n = 1.538 for crown glass for violet light.