Photoelectric Currents in Gases between Parallel Plates as a Function of the Potential Difference

Abstract

If one of two parallel plate electrodes in a gas emits photoelectrons, the current received at the collecting electrode is a function of the potential difference, the gas pressure, the initial velocity of the photoelectrons, and the mobility of the carrier. In the experiments reported here, a quartz mercury arc and a plane zinc electrode were used as the source of photoelectrons. Current: potential-difference curves were obtained for different gas pressures in hydrogen and nitrogen, and the ratio of the current, $i$, to the saturation current, ${I}_{0}$, obtained in each case. A theoretical equation of J. J. Thomson gives the relation $i=\frac{{I}_{0}{(6\ensuremath{\pi})}^{\frac{1}{2}}\mathrm{kX}}{C+{(6\ensuremath{\pi})}^{\frac{1}{2}}\mathrm{kX}}$ where $X$ is the field strength strength; $k$, the mobility of the carrier; and $C$, its random velocity. The validity of this equation is established by the experimental data which permit the values of the electron mobility $k$ to be determined as a function of $\frac{X}{p}$. Values so obtained agree well with those obtained by Loeb and by Townsend and Bailey. An equation recently given by Langmuir (Phys. Rev. 38, 1656 (1931) is shown to be applicable only at low pressures where it yields a satisfactory value of the mean free path of the electron.