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The Diatomic Chain (P.S. Lab 2)

Keywords: Normal Modes, Dispersion Relation, Fourier Analysis, Integrated Laboratory


Highlights of the activity

  1. Students are placed into small groups and use the “Waves and Optics Simulation” program to model a diatomic chain of many atoms.
  2. Each group will use the Fast Fourier Transform spectrum of the diatomic chain to find information on the normal modes, including frequency, wave vector, and wave length.
  3. Each group will be given several normal modes to investigate. At the end of the lab, the groups will bring their data together to graph the dispersion relation for the diatomic chain.

Reasons to spend class time on the activity

This activity introduces students to the analysis of a diatomic chain. For students that have less experience with Fourier analysis, taking the data for the normal modes presents an opportunity to practice using and interpreting an FFT spectrum. After finishing the activity, the dispersion relation found experimentally for the diatomic chain can be compared to the monatomic chain dispersion relation for important similarities and differences. The wrap-up of this integrated laboratory would also transition well into deriving the dispersion relation for an infinite diatomic chain, which also shows the acoustic and optical branch of the dispersion relation.


Instructor's Guide

Student Handouts


Authors: Ethan Minot, Janet Tate
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