Description
Chladni plates are used to demonstrate the complex patterns of standing wave vibrations that can occur in two-dimensional objects. These particular plates are made of iron and are caused to vibrate by stroking with a violin bow (see photograph, right). When stroked, a given plate will resonate at one of its natural frequencies. The experimenter then sprinkles fine sand, which bounces about on the plate until settling at nodal points (areas of zero movement) thereby producing intricate patterns such as the one shown below. This technique of visualisation was invented by the German physicist Ernst Chladni (1756–1827) and documented in his Die Akustic (published 1802).

Theoretically, any plate has indefinitely many possible vibration modes each corresponding to a specific frequency of sound. Each mode produces a unique pattern and the complexity of which increases with the frequency of the vibration. The shape of the patterns produced on a given plate depends on other factors, including the shape of the plate itself. One can get a sense of the variety of possible patterns from the accompanying illustration from King’s College, London, shown to the right of the plates.

Chladni plates have been used for serious research and are instructive as learning tools, but modern researchers are interested in the vibrational behaviour of more than just sheets of iron. Stringed musical instruments such as the violin and the guitar rely on the resonance of their wooden bodies to amplify and colour the sounds produced by their vibrating strings—the quality of the sound produced by a given instrument depends in large measure on the resonant properties of its top and underside plates. Chaldni’s methods can be applied to violin and guitar bodies and used by instrument builders to ‘tune’ the resonances of the instrument.


Created by: Boris Jardine