# Question #a6abc

The index of refraction is a ratio, comparing the speed of light in a vacuum ($c = 3.00 x {10}^{8} \frac{m}{s}$) to the speed of light in another substance in which the light will slow down (and therefore, refract). This relationship is shown by the formula $n = \frac{c}{v}$ where $n$ is the index of refraction of the substance and $v$ is the speed of light in whatever form of matter the light is traveling through.