This is found using a bit of geometry. All you need to know is that the sum of the three angles inside a triangle is 180 . The light is reflected off the interface, obeying the law of reflection. It then strikes the diamond-water interface. Again, the place to start is by determining the angle of incidence, .
Lenses There are many similarities between lenses and mirrors.
The mirror equation, relating focal length and the image and object distances for mirrors, is the same as the lens equation used for lenses. Also, lenses have two focal points, one on each side of the lens. The surfaces of lenses, like spherical mirrors, can be treated as pieces cut from spheres. A lens is double sided, however, and the two sides may or may not have the same curvature. A general rule of thumb is that when the lens is thickest in the center, it is a converging lens, and can form real or virtual images.