The speed of light is determined by the medium (material) through which the light is travelling. Light travels faster in a vacuum than it does in any other medium. Light changes speed as it passes ...

We can also use wavelengths to calculate refractive index. By substituting \(v_{1}=f\lambda _{1}\) and \(v_{2}=f\lambda _{2}\) into \(n=\frac{v_{1}}{v_{2}}\) then ...