For the single slit there is a well known elementary derivation along the following line: If the path difference between the elementary waves coming from the borders of the slit is one wave length you imagine say 100 elementary waves evenly distributed starting from the slit. Then the path difference between the 1. and 51. wave is so they interfere destructively, the same path difference occurs between the 2. and 52. wave, the 3. and 53, and so on. So you get a interference minimum for . If ( ) you just devide the ray bundle into bundles, where in each bundle the path difference between the "boundary rays" is and you can argue as in 1. So for each bundle you get complete destructive interference. From geometry it follows then that you get minima for where is the width of the slit. From Babinets principle it follows that the same formula should apply for the interference pattern of a opaque thin wire of thickness . Is there any direct elementary derivation (like that one for the single slit as sketched out above) for the case of the thin wire?
Elementary derivation for the minima of the interference pattern in the case of a thin wire without referring to the Babinet principle
Julia


