Light traveling in a uniform substance or medium propagates in a straight line at a relatively constant speed unless it is refracted reflected diffracted or perturbed in some other manner. Using the definition of n we can find the speed of light through lead. The index of refraction values provide a measure of the relative speed of a light wave in a particular medium.
Consider that the time for a single wavelength l to pass a point is the period of the waveform which is the reciprocal of the frequency v and you get the speed of light formula.
The speed of light in a material v v can be calculated from the index of refraction n n of the material using the equation n cv n c v. Consider that the time for a single wavelength l to pass a point is the period of the waveform which is the reciprocal of the frequency v and you get the speed of light formula. The speed of light is equal to the distance light travels d divided by the time it takes t. When light enters a substance such as glass its speed is reduced based on how it hits the atoms in the material.