Volume 5, Issue 9, 01 September 1934
Index of content:
5(1934); http://dx.doi.org/10.1063/1.1745256View Description Hide Description
Immutable conducting films, which adhere to any clean solid have been formed from synthetic resin solutions holding finely ground carbon in suspension. Values of surface resistivity for uniformly thin films were secured in the range 15 to 106 ohms referred to unit area of surface. When the thickness is held constant, the resistivity depends mainly upon the proportion of binder present and the kind of carbon used. The experimental error in repeating values of resistance with a given suspension is about ±20 percent. The dependence of resistance upon resin content of the film appears to be in accord with the views of Frenkel concerning gap contacts and in definite disagreement with the classical Maxwelltheory of composite conductors. The behavior of various types of carbon, when used in the films, can be predicted qualitatively from electrical measurements made upon powdered samples subjected to high pressure. Absorption of moisture by a film leads to a rise in resistance.
5(1934); http://dx.doi.org/10.1063/1.1745257View Description Hide Description
The fluctuation noises originating in vacuum tubes are treated theoretically under the following headings: (1) thermal agitation in the internal plate resistance of the tube, (2) shot effect and flicker effect from space current in the presence of space charge, (3) shot effect from electrons produced by collision ionization and secondary emission, and (4) space charge fluctuations due to positive ions. It is shown that thermal agitation in the plate circuit is the most important factor and should fix the noise level in low noisevacuum tubes; shot noise and flicker noise are very small in tubes where complete temperature saturation is approached; shot noise from secondary electrons is negligible under ordinary conditions; and noise from space charge fluctuation due to positive ions is usually responsible for the difference between thermal noise in the plate circuit and total tube noise. A method is deduced for the accurate rating of the noise level of tubes in terms of the input resistance which produces the equivalent thermal noise.Quantitative noise measurements by this method are reported on four different types of vacuum tubes which are suitable for use in the initial stage of high gain amplifiers. Under proper operating conditions the noise of these tubes approaches that of thermal agitation in their plate circuits at the higher frequencies and is 0.54 to 2.18×10−16 mean square volts per cycle band width in the frequency range from 200 to 15,000 cycles per second. Below 200 cycles per second the noise is somewhat larger. The minimum noise in different types of vacuum tube circuits is discussed. These include input circuits for high gain amplifiers, ionization chamber and linear amplifier for detecting corpuscular or electromagnetic radiation, and photoelectric cell and linear amplifier for measuring light signals. With the aid of these results it is possible to design circuits having the maximum signal‐to‐noise ratio obtainable with the best vacuum tubes now available.
The Behavior of a Copper Oxide Photoelectrolytic Cell When Used with Sinusoidally Varying Illumination5(1934); http://dx.doi.org/10.1063/1.1745258View Description Hide Description
Each of the copper electrodes of the cell was coated chemically with a layer of cuprous oxide. The electrolyte used was a one percent solution of lead nitrate. With an amplifier and cathode‐ray oscilloscope the open circuit e.m.f. of the cell was studied for sinusoidally varying illumination of one electrode. The frequency response, the spectral response, and the phase shift between e.m.f. and illumination were determined. A.c. bridge measurements showed that the capacitance of the cell was large and that the greater portion of it conforms to the relation for electrolytic capacitance, C=C 0/f ½. The capacitance increases with illumination. The results are interpreted in terms of an equivalent electrical network whose elements have values corresponding to those of the cell as measured with the bridge. The computed results for the network are in excellent agreement with the observed results for the cell throughout the whole frequency range (0 to 10,000) when it is assumed, (1) that the primary effect of illumination is to cause electrons to pass through the ``barrier layer'' from the oxide to the copper, and, (2) that the number of such electrons is linearly proportional to the intensity of the light. The results thus lead to the conclusion that the photoactivity of this cell is to be explained in the same manner as that of the dry cuprous oxide cell, except that the electrolyte takes the place of the front electrode in making contact with the oxide.
5(1934); http://dx.doi.org/10.1063/1.1745259View Description Hide Description
The problem of the encroachment of water into an oil sand is formulated as a new type of potential problem, namely, that of finding potential distributions in two regions of different ``constants'' (``conductivities'') which are separated by a surface, each point of which has a velocity proportional to the vector gradient of the potential at the point, and such that the area swept out by the moving interface assumes the ``constant'' appropriate to that of the encroaching side of the interface. The cases of strictly linear, radial and spherical systems, in which the shapes of the interfaces are evident from symmetry requirements, are solved in detail and discussed graphically. The zeroth approximation to the general problem which gives the history of a line of fluid particles in a homogeneous system is also treated in detail. Analytical and graphical solutions are presented for (1) systems with elliptical boundaries, (2) an infinite linear source driving fluid into an isolated sink, and (3) the history of a ring of fluid particles travelling from a source to a sink. The relation of the analytical results to the practical problems of the encroachment of water into oil bearing sands is discussed both for the solutions of the general problem and those of the zeroth approximation.
5(1934); http://dx.doi.org/10.1063/1.1745260View Description Hide Description
A method is described whereby the motion of the interface between two liquids of equal viscosity and density moving through a porous medium in systems of complex pressure distribution may be obtained by the use of electrolytic models. Experimental results for certain simple cases are compared with results obtained analytically and shown to be accurate to within 95–98 percent. Illustrations are given of more complex cases showing the application of these models to some practical problems of oil field technology.
5(1934); http://dx.doi.org/10.1063/1.1745261View Description Hide Description
A method is described for measuring the radium content of natural waters. The method is shown to be accurate to within a few percent for concentrations as low as 100×10−12 g Ra per liter. Results are given of measurements on several connate waters from mid‐continent oil fields. A correlation between radium and calcium content of the waters is indicated. Samples taken from the same wells over a period of several months indicate that the radium concentration is a definite property of a connate water.