written by Patricia Allen

When Young's double-slit experiment is conducted in undergraduate lab courses, wavelength or slit spacing is commonly calculated using Young's relation. For multi-slit gratings of 500 lines/mm, or more, few orders of interference fringes are observed, generating inaccurate and imprecise results. Here the author suggests alternate data acquisition and analysis techniques. By graphing average distance xavg from the 0th order to 1st order fringe as a function of distance from grating to screen L a linear relationship can be obtained, with the slope related to wavelength/slit spacing. With some algebra, accurate (within 1%) and precise results can be obtained. The experimental set-up used at Appalachian State University will be presented, along with sample student results, including error propagation calculations utilized during a sophomore/junior lab "intermediate" lab course (precursor to capstone lab experience).

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Last Modified January 17, 2019

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