The Periodic Emission of Light from a Discharge Tube Excited at High Frequency

Abstract

An investigation was made of the character of the light emitted by a discharge tube containing air at low pressure when the tube was driven by a high frequency oscillator. A vacuum photoelectric cell operated with an alternating driving potential of high frequency was used as a receiver. It was found that the light was fluctuating in character even when the driving frequency was as high as 10 megacycles per second, and that the average illumination lagged behind the driving potential by an angular amount which for the higher frequencies was a considerable fraction of a cycle. This indicated that the light emitted from the excited atoms persisted after excitation for a time which was of the order of magnitude of 5×${10}^{-8\mathrm{}}$ second. By using various path lengths between the source and the receiver the apparatus was also used to make a rough determination of the velocity of light. The result obtained agreed with the accepted value of light velocity within the experimental error of the apparatus, which was approximately 5 percent.