A Resonant Cavity Method of Measuring the Velocity of Light

Citation

Wohlwill, Hans Emil (1954) A Resonant Cavity Method of Measuring the Velocity of Light. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9JQK-Y835. https://resolver.caltech.edu/CaltechETD:etd-01272004-090208

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A contribution to the precision measurement of the velocity of light is described. The experiment makes use of a circular cylindrical cavity operating in the [...] mode and resonant in the 3 centimeter region. For a particular length-to-diameter ratio the resonance frequency is only a function of the cavity volume and the velocity of propagation of electromagnetic waves. The latter can be calculated from an experimental determination of resonance frequency and cavity volume. The object of this experiment was to attain an accuracy of one part in 150,000 for each individual determination. The resonant frequency was measured with a precision of one part in a million; the precision of the volume measurement was one part in 180,000. The corrections applying to both of these measurements can be calculated with sufficient accuracy to correspond to the above figures. Unfortunately, however, a time limit prevented a proper experimental determination of one correction; this concerns the shift in resonant frequency due to the iris coupling between the input wave guide and the cavity. It would be difficult to assign a numerical value to the uncertainty introduced by the lack of this information, but a minimum value for the velocity of light can be obtained. The experiments led to a probable result of 299,809 km/sec, measured with a precision of [plus or minus]1 km/sec. The extreme value of the uncertainty in the iris correction corresponds to -19 km/sec, indicating a minimum value of 299,790 km/sec. This is to be compared to the best two recent determinations whose results are 299,789 km/sec and 299,793 km/sec.

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