The Distinction between Intrinsic and Spurious Contact E.M.F.S and the Question of the Absorption of Radiation by Metals in Quanta.

Abstract

Stopping potentials for photo-electrons from Na, K and Li surfaces, as determined with a Faraday cylinder in vacuo for monochromatic ultraviolet light, were found to be accurately the same for all. This result makes general the conclusion that the stopping potential for a given frequency is the same for all clean metals. It is not the same for an oxidized copper surface, however, or for any surface showing a spurious contact e.m.f.Contact e.m.f.'s between Na, K and Li and the oxidized Cu surface of a Faraday cylinder were not found to be constant, but their changes were found to keep pace exactly with changes in the common stopping potential. These changes are attributed to the entanglement of electrons in the copper oxide surface, thus giving rise to a spurious e.m.f.Intrinsic contact e.m.f. between any two metals is shown to be a definite quantity equal to $\frac{(h{\ensuremath{\nu}}_{0}\ensuremath{-}h\ensuremath{\nu}_{0}^{\ensuremath{'}})}{e}$, when $\ensuremath{\nu}_{0}^{\ensuremath{'}}$ and ${\ensuremath{\nu}}_{0}$ are the threshold frequencies for photo-electric emission from the two metals. This equation enables intrinsic to be distinguished from spurious contact e.m.f. For if the observed contact e.m.f. differs from this value, (which it does not do for clean metals), there is a spurious contact e.m.f. equal to this difference and also equal to the difference in stopping potentials.The Photo-electric quantity hv0 is shown to be equal to the thermionic work function $\ensuremath{\varphi}e$ measured at the same temperature.Theory of photo-electric emission.---Proof is adduced for the conclusion that either the free, conduction electrons of a metal have the power of taking up the energy $h\ensuremath{\nu}$ from the incident light, or that, as Barkla has claimed, absorption does not take place in whole quanta. The difficulties associated with each conclusion are pointed out.