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Introducing the Uncertainty Principle Using Diffraction of Light Waves

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Pedro L. Muiño

Department of Chemistry, Kansas State University, Manhattan, KS 66506

J. Chem. Educ., 2000, 77 (8), p 1025

DOI: 10.1021/ed077p1025

Publication Date (Web): August 1, 2000

Section:

History, Education, and Documentation

Abstract

A thought experiment, in which a light beam is sent through slits of different sizes thereby producing a diffraction pattern, is used to illustrate the uncertainty principle. Attempts to reduce the uncertainty in the measurement of the position of the light beam () succeed, but at the expense of increasing the uncertainty in the measurement of the momentum (), so that the product of the two magnitudes, x , is still larger than h, Planck's constant. This experiment introduces the idea that one can know the value of a physical observable with as high a precision as necessary, but the act of measuring this observable has an effect on how much we can know about another observable. This thought experiment can be physically performed using a diode laser and a series of slits. A derivation is presented to relate the uncertainties in position and momentum to variables that can be measured with a ruler in a classroom or laboratory. Data from a typical experiment are also presented.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Demonstrations

Keywords (Subject):

Lasers

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Single-Slit Diffraction and the Uncertainty Principle
Frank Rioux
Journal of Chemical Education2005 82 (8), 1210
- Single-Slit Diffraction and the Uncertainty Principle
  Frank Rioux
  Journal of Chemical Education2005 82 (8), 1210
  This short article emphasizes that a consideration of diffraction phenomena is an excellent way to illustrate the uncertainty principle. Or, it could also be claimed that diffraction has a simple quantum mechanical interpretation based on the uncertainty ...
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