Now, let us see, when we will observe maxima in diffraction pattern.

At the center of screen, the path traveled by the secondary waves originating from one point of slit is same as that traveled by another wave on the opposite side of center of slit at the same distance and hence path difference is zero, ie all the waves meet in phase thus we observe a maxima at this point (Fig 3). This can also be seen mathematically for the intensity distribution equation for point , and (for small , the series expansion of will contain only first term ). Thus the intensity at the center will be

                         

Now we will determine the position of the maxima.

                       

                             or