Study of some problems arising from spontaneous fluctuations of electricity

Abstract

In this thesis we have studied a number of problems of electrical fluctuations whose common initial origin lay in the fundamental significance of "shot" and "thermal" fluctuations.

First, a theoretical and historical study was presented of the space - charge reduction of fluctuations in thermionic valves leading to a unification of the concepts of shot and thermal noise therein. In particular we observed that the common origin becomes most obvious when retarding field conditions obtain; a theoretical and experimental study of the retarding field region was therefore then undertaken. This included measurements to investigate and confirm the valve characteristics in that region and experimental observation of the fluctuations under true retarding conditions. The criteria relevant to entry into the region were also examined. As a by-product of the 'experimental fluctuation measurements, work was also undertaken on photo-electric cells and an interesting field of investigation is indicated by the results obtained.

Finally, detailed statistical examination was presented of fluctuation records with relevant derived theory in which satisfactory agreement was obtained; this provided also experimental confirmation of previously known theoretical results. A possible indication of discrimination was observed between noise generated by a valve working under saturation conditions and that generated by thermal agitation in a tuned circuit such that it might possibly be accounted for by a certain degree of interaction between the primary events in the latter case.

We should emphasise however, particularly in view of Chapter 2, that we are convinced that all these phenomena should be classed as thermal agitation, the terms "shot noise" and "thermal noise" being employed solely as a convenient classification indicating the electrical element wherein the fundamental phenomenon is manifested