Plane wave fronts are shown in two mediums. Find the refractive index of the second medium

Spacing between two consecutive wavefronts represents wavelength of a wave.

$$\begin{gathered} Hence, {\lambda }_1 = 2m and {\lambda }_2 = 1m \\ Also, refractive index , \mu =\frac{c}{f\lambda } \\ In refraction speed of light c and frequency f doesn\text{'}t change. \\ \therefore \mu \propto \lambda \\ \Rightarrow \frac{{\mu }_2}{{\mu }_1} = \frac{{\lambda }_1}{{\lambda }_2} \\ \Rightarrow \frac{{\mu }_2}{1}=\frac{2}{1} \\ \Rightarrow {\mu }_2 = 2 \end{gathered}$$