Wave Mechanics Lecture Demonstrations
Standing Waves on a String
Waves on a string are the classic model for electron density in a 1-dimensional box. If a standing wave generator isn't available, one can be made from the vibrator in an aquarium air pump .
Single Slit Diffraction
To show that light has properties that cannot be explained except by a wave model, we create a single slit diffraction pattern on a wall or projection screen in the following manner: Two single edged razor blades are taped together, sharp edge to sharp edge, to form a very narrow slit. a red or green laser pointer is held close to the slit, and the image is projected 30-40 ft, if possible, on the screen or wall. For particulate model (unless probabilities are calculated with a wave model), we would expect to see the laser dot cut off on two sides; instead, we see the diffraction pattern of alternating bright and dim bands. This is analogous to the maxima and nodes of the vibrating string.
If commercial Chladni Plates with electronic frequency drivers are not available, they can be easily constructed  and used to demonstrate two dimensional standing wave patterns. Various shapes of steel plates (~3/32" thick) can be bolted to angle brackets and clamped to a table top. We use 12" x 12" squares, bolted at the centers. The plates are "struck" (violin style) with a bow constructed by stringing "weed wacker" nylon string on the frame of a bow saw.