SKEDSOFT

      fig..(3)            

         or,    

         or,         the two minima coincide.

Width of principal maxima :The width of principal maxima in this case is given by the distance between two points on screen when first order diffraction minima occurs i.e. if D is separation between slit and screen and z is the linear separation between first diffraction minima and central maxima, then for small

Width of principal maxima Fringe width The fringe width in the double slit diffraction pattern is same as the fringe width in the case of double slit interference ie the fringe width

Missing Orders In the intensity distribution curve in double slit diffraction pattern : Any particular order interference maxima may be absent if it coincides with the diffraction minima. These missing orders ( p values) in interference will be given by the condition.

                   or       

Thus if the separation between slit is 10 times the slit width, the 10 order interference maxima will coincide with the first order diffraction minima and 20^th order interference maxima will coincide with 2^nd order diffraction minima and thus 10^th , 20^th, 30^th , ---- order interference maxima will be missing.