In trying to get a better understanding of the double slit interference phenomenon, a Physics student sets up two slits in such a way, where a thin piece of clear glass (n = 1.57) covers one of the slits on the side facing the screen. A semiconductor laser illuminates the slits from the other side (wavelength = 638 nm).
It is noticed that the central region on the screen is now covered by what was previously the m = 10 dark fringe. How thick is the glass?