Problem

A thin flake of mica (n=1.58) is used to cover one slit of a double slit arrangement. The central point on the screen is now occupied by what had been the seventh bright fringe (m=7) before the mica was used. If ?= 550 nm, what is the thickness of the mica?

A thin flake of mica (n=1.58) is used to cover one slit of a double slit arrangement. The central point on the screen is now occupied by what had been the seventh bright fringe (m=7) before the mica was used. If ?= 550 nm, what is the thickness of the mica?