Refraction:

Early peoples doubtless observed refraction and also reflection; a clear pond appears shallower than it really is since of this effect. The Refraction is related with the fact that various media transmit light at various speeds. This does not break the basic principle of relativity theory. The speed of light is fixed in a vacuum, where it travels at around 299,792 km/s (i.e., 186,282 mi/s), though light travels more slowly than this in the other media.

In air, the variation in the speed of light is small as compared with its speed in a vacuum, however it can be significant sufficient to generate refractive effects at near-grazing angles among air masses containing various densities. In glass, water, quartz, diamond, & other transparent media, light travels quite a lot more slowly than it does in a vacuum. The refractive index, also termed as the index of refraction, of a medium is the ratio of speed of light in a vacuum to the speed of light in that medium. When c is the speed of light in a vacuum and cm is the speed of light in medium M, then index of refraction for the medium M, let say it r_m, can be computed simply:

r_m = c/c_m

Always use similar units whenever stating c and c_m. According to this description, the index of refraction of some transparent material is forever greater than or equivalent to 1.

The greater the index of refraction for a transparent material, the more light is bent whenever it passes the boundary among that substance and air. Various types of glass have dissimilar refractive indices. The Quartz refracts more than glass, and diamond refracts more than the quartz. The high refractive index of diamond is answerable for the multi-colored shine of diamond stones.