A slit S is illuminated by a monochromatic source of light to give two coherent sources `P_1`, and `P_2`, These give a dark band at a point on the screen If the distance between `P_1`, and `P_2`, is 1 mm and the screen is placed in 1m away, what is the fringe separation for a light of wavelength `5 x 10^-7`m?