In a Young's double-slit experiment using monochromatic light, the fringe pattern shifts by a certain distance on the screen when a mica sheet of refractive index 1.6 and thickness 1.964μm is introduced in the path of one interfering wave. The mica sheet is then removed and the distance between the slits and screen is doubled. It is found that the distance between successive maxima or minima is then the same as the fringe shift caused by the mica sheet. Calculate the wavelength of the monochromatic light used.