Diffraction as a Consequence of Faraday's Law
  We consider a linearly polarized electromagnetic wave incident on an opaque screen with square aperture of edge a. An application of Faraday's law to a loop parallel to the screen, on the side away from the source, shows that the wave must have longitudinal components there. The ratio of the longitudinal to transverse field is a measure of the diffraction angle. 
Max S. Zolotorev, Kirk T. McDonald