When light is refracted from a vacuum injection medium, the ratio n of the incident angle i to the sine of the refraction angle r is called the "absolute refractive index" of the medium, referred to as "refractive index". It represents a characteristic of the medium to light as it propagates through the medium.
[Formula]: n=sin i/sin r=c/v
Since the light travels at a maximum speed in a vacuum, the refractive index of other media is greater than one. The same medium has different refractive indices for light of different wavelengths; in a medium transparent to visible light, the refractive index often increases with decreasing wavelength, that is, the refractive index of red light is the smallest, and the refractive index of purple light is the largest. Generally speaking, the refractive index value of an object (for example, water is 1.33, crystal is 1.55, diamond is 2.42, glass is 1.5 to 1.9 according to composition), and refers to sodium yellow light (wavelength 5893×10^-10 meters). ).