by Thomas Lang
A one-dimensional model showing a particle in a box with reflecting boundary conditions and a delta-function barrier in the middle.
A Gaussian wave packet hits the delta function barrier (a semitransparent mirror) from the left. A part of it gets reflected and another part gets transmitted. The two parts are then reflected by the Dirichlet boundary conditions (mirrors) at +5 and -5 and recombined at the delta barrier. Here the left moving parts interfere destructively, and the right-moving parts interfere constructively.
Mathematica Notebook (in German)