In a young's double slit experiment a thin sheet of mica is placed over one of the two slits. As a result, the center of the fringe pattern shifts by 30 bright fringes. The wavelength of light in the experiment is 480 nm and the index of refraction of the mica is 1.60. The thickness of the mica is?
The Attempt at a Solution
Without considering the effect of the mica we have that the phase difference between the slits will be ##30\lambda## however I am stuck trying to figure out how to account for the additional phase difference when the mica is placed.