Question

The refractive index of diamond in much greater than that of ordinary glass. Is this fact of some use to a diamond-cutter?

Answer 1

Refractive index of diamond is nearly 2.42. It is much larger than that of ordinary glass (nearly 1.5). The critical angle for diamond is nearly ${24}^0$. This is much less than that of glass. A skilled diamond cutter exploits the large range of angle of incidence (in the diamond) ${24}^0$ to ${90}^0$, to ensure that light entering the diamond is totally reflected from many faces before getting out. This produces sparkling effect in the diamond.