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  Home > JCE Print > Journal of Chemical Education > Issues > 2000  > August  >
In the Classroom
Introducing the Uncertainty Principle Using Diffraction of Light Waves
Pedro L. Muiño
Department of Chemistry, Kansas State University, Manhattan, KS 66506
Cover
August 2000
Vol. 77 No. 8
p. 1025
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.
More Information
*  Citation
 Muiño, Pedro L. J. Chem. Educ. 2000 77 1025.
*  Keywords
 Demonstrations; Lasers / Laser Spectroscopy; Physical Chemistry; Quantum Chemistry
*  History
 Created:
Last Updated:		 July 5, 2000
April 15, 2005
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