A ray of light has speed $\left({\mathrm{v}}_0\right)$ frequency $\left({\mathrm{f}}_0\right)$ and wave length $\left({\mathrm{\lambda }}_0\right)$ in vacuum. When this ray of light enters in a medium of refractive index $\left(\mathrm{\mu }\right)$, corresponding values are $\mathrm{v},\mathrm{f}$ and $\underset{\_}{\mathrm{\lambda }}$ . Then