Two light rays initially in the same phase travel through two media of equal length $L$ having refractive indices $\mu_1$ and $\mu_2$ (where $\mu_1 > \mu_2$) as shown in the figure. If the wavelength of the light rays in air is $\lambda$,the phase difference of the emerging rays is given by:

• A
  $\frac{L \mu_1}{\lambda \mu_2}$
• B
  $\frac{(\mu_1-\mu_2) L}{2 \pi \lambda}$
• C
  $\frac{2 \pi(\mu_1-\mu_2) L}{\lambda}$
• D
  $0$