The threshold potential,light-effect and chemical reactivity under electrical discharge

Summary

From an observation of a photo-increase of the minimum threshold potentialV _m , that the currenti at a givenV should decrease under light was predicted by the author from a finding thati depends uponV-V _m . Presumably, the magnitude of a chemical reaction under discharge does not depend appreciably on the corresponding high frequencies produced; these, however, constitute the main source of thelight-effect. Furthermore, in contrast with a chemical reaction which is minimum atV _m , thelight-effect observed with a number of A.C. indicators, and expressed as percentage ofi is a maximum nearV _m . This, together with a general finding that thelight-effect is not sensible belowV _m , suggests that an optimum condition for its occurrence is a transition state, within which the conductivity of the gas changes from the dielectric to the ohmic type. The ‘electron affinity’ of the excited gas is another important determinant of this phenomenon.