# What is Snell's Law?

#### Editorial Team - GoPhotonics

Sep 19, 2023

Snell's Law, also known as the Law of Refraction, is an equation that connects the angle of the incident light and the angle of the transmitted light at the interface of two different media. The law states that the ratio of the sine of the angles of incidence and transmission is equal to the ratio of the refractive index of the materials at the interface.

Where n1 and n2 are the two different media

θ1 is the angle of incidence and θ2 is the angle of reflection

This law is named after Dutch mathematician and astronomer Willebrord Snellius. It can be applied to all materials, in all phases of matter.

Refraction is the phenomenon in which a light wave bends as it travels from one medium to another. When light moves from a rarer medium to a denser medium, it bends toward the normal to the boundary between the media. Conversely, when light passes from a denser to a rarer medium, it bends away from the normal.

Speed of light is given by:

V is the velocity in the medium, n is the refractive index of the material and c is the speed of light in a vacuum.

The law connects the sines of the angles of incidence and transmission to the index of refraction for two different mediums.

Where the angles are measured from the normal line at the interface

Snell’s Law is derived from Fermat’s principle, which states that light travels in a path of least time.

When light travels from a denser medium to a rarer medium, it bends away from the normal and vice versa. This bending is determined by the refractive indices of the mediums involved.

Applications of Snell’s Law

One of the important applications of Snell's Law is found in the domain of Fiber Optics. This technology serves crucial roles in various fields, such as telecommunications and high-speed data transmission within servers. It is also used in optical apparatus such as eyeglasses, contact lenses, cameras, and rainbows.