An empirical equation use
An empirical equation used to find this value sets it equal to B plus the sum of B-n over a given wavelength to the n-th power where n goes from two to infinity. The variation of this quantity with respect to wavelength is given by the Abbe number. Minerals such as Icelandic spar have two values for this quantity and are therefore birefringent. Water has a value of one and a third for this quantity, which is multiplied by the sine of the angle of incidence is used in Snell's law. For 10 points, name this quantity that is defined as the ratio of the speed of light in vacuum to the speed of light in a material.
An empirical equation used to find this value sets it equal to B plus the sum of B-n over a given wavelength to the n-th power where n goes from two to infinity.
Refractive index [or index of refraction]