# Measurements of the ratio of charge to mass of free electrons using a resonant cavity

Abstract (Summary)

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A deflection method for measuring (e/m[subscript o]) for free electrons is described. A beam of electrons is directed along the axis of a cylindrical cavity excited in the TM[...] mode. A null in the subsequent deflection of the beam occurs when the transit time is nearly equal to an integral number of cycles of the cavity oscillation. The average velocity of the electron beam is calculated from knowledge of the cavity dimensions and the resonant frequency of the cavity. The value of (e/m[subscript o]) is obtained by equating the energy required to accelerate the electrons and their kinetic energy. Three quantities must be measured, a distance, a frequency and a difference of potential, and two very small corrections most be made. Errors due to unmeasurable work function potentials, etc., are eliminated by taking two sets of data with different transit times and subtracting the two energy equations. A probable error of less than 1 part in 10,000 sees to be achievable. Preliminary apparatus gave a value (e/m[subscript o]) = 1.759 [plus or minus] .007 (10)[superscript 7] emu per gram.
Bibliographical Information:

Advisor:W. R. Smythe

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis

Keywords:engineering and applied science

ISBN:

Date of Publication:01/01/1948