Refraction

Refraction is the change in direction of a light ray due to a change in the speed of light as it changes medium. The index of refraction describes the optical density of a material and is equal to the speed of light in vacuum divided by the speed of light in the material. Snell’s Law describes the relationship between the indices of refraction, the angle of incidence and the angle of refraction. When light travels to a less optically dense medium, it speeds up and bends away from the normal. When light travels to a more optically dense medium, it slows down and bends toward the normal. Total internal reflection can occur when light is traveling from a more to a less optically dense medium and the angle of incidence is greater than or equal to the critical angle. When total internal reflection occurs, no light leaves the incidence medium. Fiber optics takes advantage of total internal reflection to carry communications signals using light.