AAI ATC Junior Executive 2018 Shift 1 Paper

In an experimental arrangement of a Fresnel' biprism, monochromatic light of wavelength λ is used to produce interference fringe pattern. On introducing a thin, transparent glass sheet of refractive index 1.50 and thickness of 7 microns in the path of one of the interfering beams, the central fringe of the pattern is shifted to the position of 6th bright fringe. Then, the wavelength λ of the monochromatic light used is nearly: