Interference fringes are produced by fresnel''s biprism in the focal plane of an eyepiece 200 cm away from the slit.Two images of the slit that formed each of the two positions of a convex lens placed between the biprism and the eyepiece are found to be separated by 4.5 mm and 2.9 mm respectively. If the width of the Interference fringes be 0.326 mm, find the wavelenth of the light used.