Journal of Chemical Education

Introducing the Uncertainty Principle Using Diffraction of Light Waves

Pedro L. Muíño

Published Aug 1, 2000• 14 citations

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.

DOI: 10.1021/ed077p1025

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