Task: Text Categorization
Input (English): One way of calculating this quantity compares it to a standard of this value which can be calculated by the Edlen equation and involves finding the angle of minimum deviation. This quantity is modeled by the sum of a constant term and a term inversely proportional to wavelength squared in the (*) Cauchy equation, which is generalized to a three-term expansion by the Sellmeier equation. This quantity is related to polarizability by the LorentzLorenz equation, and it equals the square root of the product of relative permeability and permittivity. The Fresnel equations describe light moving between media with different values for this quantity, which is one for a vacuum. For 10 points, name this quantity which appears in Snell's law, the ratio of the speed of light in a vacuum to that in a medium.
Output (English): Science