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Guitar Strings as Standing Waves: A Demonstration

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Michael Davis

Physical Science Department, Harold Washington College, Chicago, IL 60601

Todd P. Silverstein

Department of Chemistry, Williamette University, Salem, OR 97301-3922

Dean J. Campbell

Department of Chemistry, Bradley University, Peoria, IL 61625-0208

J. Chem. Educ., 2007, 84 (8), p 1287

DOI: 10.1021/ed084p1287

Publication Date (Web): August 1, 2007

Section:

History, Education, and Documentation

Abstract

An undergraduate student's first exposure to modern atomic theory tends to start with Bohr's model of the atom. This familiar introduction to atomic structure also marks a general chemistry student's first foray into waves. Many popular chemistry textbooks illustrate the concept of a standing wave in the development of the modern quantum model by using the phrase “as seen on a guitar string”. In these illustrations, the wave itself is often small and difficult to discern. The same phenomenon, however, can be easily and audibly observed. This demonstration uses an acoustic guitar to produce three unique harmonic vibrations, each of which is representative of a standing wave and illustrates the concept of quantization. Manipulation of the guitar string to produce a standing wave is pervasive in popular music and is audibly recognizable. Lightly placing a finger on the 12th, 7th, or 5th fret and strumming any one or all six strings can produce an audible example of a standing wave on a guitar. This corresponds to a standing wave with 1, 2, or 3 nodes, respectively. Attempting to induce a node at other points on a guitar string does not generate a standing wave, due to destructive interference, thus no audible tone is produced.