Refraction Refraction refers to the bending of the transmitted light at the interface between two transparent materials. The angle of refraction depends on the angle of incidence and the relative speeds of the light in the two different media and can be found from the relationship [pic] From this equation we see that the direction in which the light is bent depends on whether it is going from a slower to a faster medium or vice versa. Index of refraction The index of refraction of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in the medium. pic] By definition, n = 1 in vacuum. In all materials n > 1. The frequency of light does not change as it goes from one a medium of one index of refraction to another. This means that the wavelength changes with the speed. [pic] Thus, the wavelength is smaller in a medium than in vacuum. From the definition of the index of refraction, we can rewrite the relationship between the incident and refracted angles as Or [pic] This equation is known as Snell’s law of refraction. Example The index of refraction of a glass is n = 1. 6.
A ray of light is incident upon the glass surface at an angle of 30o. What is the angle of refraction into the glass? Solution: Assume that air surrounds the glass and that the index of refraction of air is approximately n = 1. [pic] If the wavelength of the light in air is 520 nm (green), what is its wavelength in the glass? [pic] What is the frequency of the light? [pic] Or [pic] [pic] What is the frequency of the light? [pic] ———————– (1 (1’ (2 slow fast incident reflected v2 > v1 incident (1 (1’ (2 v2 < v1 fast slow reflected refracted