# Details for the Chladni Plate Demo

This is a Chladni plate we use to demonstrate resonance to our students. It was suggested by Tom McMath, built by Bob Chin and is used to demonstrate resonance on a 2-dimensional surface. Our apparatus uses a large (approximately 1 square metre) metal plate with a sturdy stand supporting the plate in the centre and a mechanical vibrator (Pasco SF-9324) driven by a frequency generator (Pasco PI-9587 precise to +/- 0.01 Hz). An article that suggests using such a large plate (but using a violin bow to create the vibrations on the plate) is "Chladni Plates: How Big can They Be?", found in The Physics Teacher, Vol. 34, Nov. 1996, pp.508-509.

Most people first encounter resonance in the form of standing waves on a string. One end of the string has a vibrator attached to generate a ripple or wave on the string. The wave moves along the string. Upon reaching the end of the string, the wave reflects or bounces back. Over and over, waves travel the string and reflect at the ends. All the waves, the original and reflected waves, interfere with one another and often mostly cancel one another out. At certain special or resonance frequencies the peaks in the waves all line up and a pattern will emerge as shown in the diagram below.

Parts of the string move up and down. The places where the amplitude of the motion is greatest are called Antinodes. The places that don't move at all are called Nodes. On a 2-dimensional surface, nodes form lines on the surface.  The pattern of the  nodal lines depends on the particular resonance frequency. Sand is poured on a vibrating Chladni plate to make the nodal lines visible. The moving areas of the Cladni plate cause the sand to move to the non-moving nodal lines.

Picture of the vibrator underneath the Chladni plate.