In a two-slit experiment using monochromatic light, fringes are observed on a screen at a distance from the slits. The screen is moved by `5 xx 10^-2` m towards the slits and the change in fringe width is found to be `3 xx 10^-5` m. The distance between the slits is `10^-3`m. Find the wavelength of the monochromatic light used.