Ray Optics

Light of wavelength \(300 \mathrm{~nm}\) in medium \(A\) enters into medium \(B\) through a plane surface. If the frequency of light is \(5 \times 10^{14} \mathrm{~Hz}\) and the ratio of speed in medium \(A\) to that in medium \(B\) is \(4 / 5\), the absolute refractive index of medium \(B\) is