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 manifeste
