Chladni's Plates

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A two dimensional standing wave demonstration.

Originally Chladni drew a rosin coated bow over a supported metal plate sprinkled with sand. When the plate was touched at points along the edge standing waves were produced and the sand produced interesting patterns. The pattern depends on where you bow, and on the shape and size of the plate. The higher the harmonic, the more complex the pattern produced

square plate in use

A similar, and easier to reproduce, effect can be acheived using a signal generator , vibration generator and plate.

Commercial plates are available from educational suppliers and usually found in the sound section of catalogues.

The vibration generator usually has a 4mm plug or 2BA screw fitting. A simple aluminium or steel plate can be used. The centre is carefully measured and drilled so this can be fixed to the vibration generator by a suitable connection. Wedges may be required to level the plate.

Dry sand is then sparingly sprinkled over the surface of the plate and the frequency varied until a resonance is heard. At this point there will be a characteristic pattern forming on the plate. Caution should be used as at higher frequencies the sound can be quite intense.

The mathematical analysis of these patterns can be quite involved, but the sudden changes can be quite impressive.

External links

--D.B.Ferguson 20:26, 2 March 2007 (GMT)

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