rate of speed of light in a vacuum to that in a medium is called
The speed of light in a given material is related to a quantity called the index of refraction, n, which is defined as the ratio of the speed of light in vacuum to the speed of light in the medium: index of refraction: n = c / v.When light travels from one medium to another, the speed changes, as does the wavelength.efraction. When we talk about the speed of light, we're usually talking about the speed of light in a vacuum, which is 3.00 x 10 8 m/s. When light travels through something else, such as glass, diamond, or plastic, it travels at a different speed.