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The Dance of the Standing Waves


A high-resistance chrome-nickel wire was heated by passing an electric current through it. This caused the wire to glow with bright red (black-body) radiation. A vibrating motor placed at one end was used to create standing waves. Photos of the standing waves were taken using a two second exposure. In this photo during the first second of exposure there were standing waves as planned. The nodes of the standing wave are characterized by a relatively high light intensity. This is because these points do not move and more light accumulates from them. The vibrating parts are less intense, but at the points of maximal amplitude the intensity is higher due to the slower motion there. AAPT Summer Meeting 2013 logoAnother factor that influences the difference in intensity is that the vibrating parts are cooled to a greater extent by the air. After about one second the string was accidentally torn off, resulting in a unique and spectacular pattern of light.As can be seen, the middle part went up while the sides went down, reflecting the opposite motion of these parts in the standing wave. In addition, the string moved to the left, reflecting the fact that it was torn on the right.Note that the points that were previously close to the nodes are more intense. Since it took time for the perturbation to reach the left side, the displacement of the right parts was greater than that of the left parts. The picture dramatically illustrates the regular motion of the standing waves and the complex unpredictable behavior of the torn string.


Photo submitted by Shalev Manor while attending the Israeli Arts and Science Academy in Jerusalem in 2005. Teacher: Paul Gluck


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Go back to the April 2013 eNNOUNCER.

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