Figure 9 shows an example of a diffraction pattern from a single slit. Again, several features are noteworthy.
Figure 9: Intensity as a function of observation angle for a
finite-slit experiment
This corresponds to , a path difference between one end of the slit and the other of any non-zero integer number of wavelengths. If the path difference is zero, all the contributions interference constructively, and you get a large maximum. If the path difference is not zero, but an even number of wavelengths, then we see that you always find exactly canceling negative and positive contributions from difference regions of the slit, leading ultimately to a minimum.