Ray Of Light Compared To The Interface Between Two Mediums

A ray of light travels in a straight line. This is true until it passes from one medium (eg. air) into another medium (eg. glass) of a different optical density. When this happens, the ray of light changes speed causing it to bend either towards or away from the normal which is an imaginary line at 90 to the interface between two mediums. This is called refraction. How much it bends depends on the refractive indices of the two mediums which is a ratio of the speed of light in one medium compared with the second.

For example the refractive index (n) of crown glass can be calculated as it passes from air into crown glass

Total internal reflection occurs when the refractive index of the first medium is more than that of the second. The angle of incidence is the angle that a ray of light hits an interface between two mediums relative to the normal. As this angle becomes greater, less of the light is refracted and more of it is reflected until an angle of incidence is reached where the angle of refraction (angle of ray in second medium relative to the normal) equals 90. This angle of incidence is called the critical angle. …show more content…
For example, the core could be made of flint glass with a refractive index 1.62 and the cladding of crown glass with 1.52 for a refractive index.
The critical angle of this situation can be calculated as