A thin mica sheet of thickness $2\times {10}^{-6}\mathrm{m}$ and refractive index $(\mathrm{\mu }=1.5)$ is introduced in the path of the first wave. The wavelength of the wave used is 5000 Å. The central bright maximum will shift

• A

  2 fringes upward

• B

  2 fringes downward

• C

  10 fringes upward

• D

  None of these