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Molecular Structure from Scattering Phenomena

  • Peter R. Bergethon
Chapter

Abstract

We noted in Chapter 6 that when waves interact there will be interference that is either constructive or destructive. All waves, whether of sound, water, or light, will exhibit spatial interference patterns. If two point sources are each generating coherent (in-phase) waves, patterns of brightness and darkness will be seen coinciding with the constructive and destructive interference of the waves, respectively (Fig. 29.1). The reason for the interference pattern can be physically appreciated by an experiment in which a single source of sine waves (such as a sound) is played into two tubes of different length that terminate at a microphone that displays the arriving waves on an oscilloscope. At the beginning of the tubes, each wave is in phase with the other. But though the waves start in phase, when they reach the ends the tubes, because of the different path lengths, they will not necessarily still be in phase. If the two paths are equal, then the wave peaks will reach the microphone at the same time, and they will interfere constructively. If the length is different, then interference will also occur, but whether it is destructive or constructive will depend on the difference in length \(L_2 - L_1 = \Delta L\) of the path. If \(\Delta L = \lambda /2\) then a wave peak and trough will reach the microphone simultaneously, the phase difference will be 90° and the interference will be completely destructive. Any length in between will give an intermediate amplitude. For the two extreme conditions of interference:

Keywords

Point Source Incident Wave Scattered Wave Destructive Interference Miller Index 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  1. 1.Departments of Anatomy & Neurobiology and BiochemistryBoston University School of MedicineBostonUSA

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