In a double slit experiment the distance between the slits is 0.1 cm and the screen is placed at 50 cm from the slits plane. When one slit is covered…

In a double slit experiment the distance between the slits is $\displaystyle 0.1$ cm and the screen is placed at $\displaystyle 50$ cm from the slits plane. When one slit is covered with a transparent sheet having thickness $\displaystyle t$ and refractive index $\displaystyle n(=1.5)$, the central fringe shifts by $\displaystyle 0.2$ cm . The value of $\displaystyle t$ is $\displaystyle \_\_\_\_$ cm.