With the double slit experiment, if the slits are too far apart or too wide, light from the slits does not overlap and no interference pattern is observed.In the single slits experiment, if a parallel beam is directed at a single slit it produces a diffraction pattern on a white screen.There is a central fringe with fringes on either side.The width of the central maximum is double the width of the other maxima and is given by W = 2λD/a where a is the width of the single slit gap and D is the distance from slit to screen.The intensity is greatest at the centre, and the peak intensity decreases with distance from the centre.Each of the outer fringes is the same width and is of much less intensity than the central fringe.