Wave Mechanics Lecture Demonstrations - ChemPRIME

Wave Mechanics Lecture Demonstrations

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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 [1].

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.

Chladni Plates[2]

If commercial Chladni Plates with electronic frequency drivers are not available, they can be easily constructed [3] 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.


References

  1. J. Chem. Educ., 1996, 73 (2), p 171
  2. http://en.wikipedia.org/wiki/Chladni
  3. J. Chem. Educ., 1996, 73 (2), p 171
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