The Energy Losses Attending Field Current and Thermionic Emission of Electrons from Metals

Abstract

The energy losses accompanying field emission and thermionic emission have been measured in the same experimental tube. This was accomplished by observing the thermal electromotive force in a junction from which the emission currents were drawn. No measurable temperature change was observed for field emission up to thermionic temperatures. For thermionic emission, temperature changes were observed which, when correlated with the power losses from the filament as a function of temperature, yield a calorimetric value for the work function of tungsten of 4.46\ifmmode\pm\else\textpm\fi{}0.09 volts. A theoretical expression is given for the average net energy loss per electron emitted in thermionic and field current emission. The experiment gives strong additional evidence that in field emission the electrons escape by penetrating rather by surmounting the surface potential barrier as in thermionic emission.