The Velocity of Propagation of Electromagnetic Waves Derived from the Resonant Frequencies of a Cylindrical Cavity Resonator
Abstract
The cavity resonator used in this investigation is a silverplated steel cylinder 6\cdot 5 cm. in diameter and of adjustable length. Resonance in the H_{011} mode is established at a frequency in the region of 9000 Mc./sec., and the length is then varied to give successive resonances at half wavelength intervals. The wavelength is thus determined and this, together with the frequency, the diameter and a correction term involving the sharpness of resonance, enables the velocity to be calculated. This procedure has some advantage over that used previously by Essen & GordonSmith in which the measurements were made with a resonator of fixed dimensions. The wavelength is determined only from differences in length, the first resonant length not being used, and in this way certain endeffects, such as those due to the coupling loops and to surface imperfections, are eliminated or greatly reduced. Moreover, by using different frequencies, or different modes at the same frequency, the diameter can be eliminated from the calculations and a value of c thus obtained in terms of frequency and length both of which can be measured with high precision. The result obtained is 299, 792\cdot 5 ± 3 km./sec., and is thus in close agreement with that obtained by Essen & GordonSmith with a fixed cavity and also with the value of c determined recently by Bergstrand with an optical method.
 Publication:

Proceedings of the Royal Society of London Series A
 Pub Date:
 December 1950
 DOI:
 10.1098/rspa.1950.0172
 Bibcode:
 1950RSPSA.204..260E