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Form of solution from a narrow slit

Because we consider a slit which is much narrower than the wavelength of the waves passing through it, physically there is no way for the waves to distinguish the slit from a tiny point source of waves. This is known as Huygen's principle. Mathematically, it is the same principle which makes the electric potential at a distance r far away from a distribution of charges which are spread out over a small distance d<<r go just like the field from a single point charge, k Q/r, regardless of exactly how the charges are arranged.

Tomas Arias
Thu Sep 13 15:26:14 EDT 2001