To show the two-dimensional standing waves on the surface of a square or circular plate. A frequency generator is connected to a mechanical vibrator. The vibrator drives a Chaldni plate, as shown in the photo at the left.
White sand is sprinkled randomly to cover the entire black surface of the plate.
Drive the plate at a predetermined harmonic frequency and the sand will migrate into the nodal regions. A well defined standing wave pattern can be clearly seen in the photo at right. The circular and square Chladni plates will create characteristic patterns. Adjust the oscillator slowly in the .3 to 2 kHz frequency range and watch for the pattern to emerge when a harmonic is tuned. This experiment is very dramatic yet very simple to operate.