Volume 31, Issue 11, November 1963
Index of content:
31(1963); http://dx.doi.org/10.1119/1.1969133View Description Hide Description
Prepared at the request of the AAPT Committee on Resource Letters; supported by a grant from the National Science Foundation.
This is one of a series of Resource Letters on different topics, intended to guide college physicists to some of the literature and other teaching aids that may help them improve course contents in specified fields of physics. No Resource Letter is meant to be exhaustive and complete; in time there may be more than one letter on some of the main subjects of interest. Comments and suggestions concerning the content and arrangment of letters as well as suggestions for future topics will be welcomed. Please send such communications to Professor Arnold Arons, Chairman Resource Letter Committee, Department of Physics, Amherst College, Amherst, Massachusetts.
Notation: The letter E after an item number indicates elementary level, useful principally for freshman liberal arts through sophomore physics courses; the letter I indicates intermediate (junior, senior) level; and the letter A indicates advanced material principally suited for senior, graduate study. An asterisk (*) indicates items particularly recommended for introductory study.
Additional copies: Available from American Institute of Physics, 335 East 45 Street, New York 17, New York. When ordering, request Resource Letter FC-1, and enclose a stamped return envelope.
31(1963); http://dx.doi.org/10.1119/1.1969135View Description Hide Description
Elementary treatments of a single angular momentum having components usually go as far as discussions of the spectra of these operators and the derivations of their standard, i.e., -diagonal, representatives. On the other hand, the standard representatives of their eigenvectors are not usually obtained, leaving aside, for which the problem is trivial. In fact, this part of the theory is most often dealt with only after a lengthy excursion into the theory of matrix representations. The representatives in question are obtained, in the first part of this paper, by means of essentially elementary arguments. Once these representatives are known, the standard representative of the unitary operator which generates the state vector of a system after it has undergone a rotation from the state vector prior to the rotation are deduced; this representative comprises just the familiar matrix representations of the rotation group. Finally, the relevance of harmonic oscillatortheory to the present problem is briefly considered.
31(1963); http://dx.doi.org/10.1119/1.1969136View Description Hide Description
The classical statistical mechanical theory of one-dimensional systems of particles which interact only with their nearest neighbors is applied to a simple model of a solid. The relative distance between neighboring particles is limited to a finite range by the form of the assumed interaction potential. The virtue of the model is that simple exact expressions are obtained for the coefficient of thermal expansion and Young's modulus when the pressure on the system is zero.
An Experiment Offering Varied Experience: Conductivity Changes of a Germanium Crystal under Tension and Illumination31(1963); http://dx.doi.org/10.1119/1.1969137View Description Hide Description
Using Bridgman's compensated potentiometer method an experiment is described in which the electrical resistance of a single germanium crystal may be shown to change when illuminated and when under tension, both well-known effects. The procedure sketched here differs from those usually employed in this field and gives experience in a number of different techniques and types of measurement. It is capable of showing that the effect of tension and the effect of illumination on the resistance are independent of each other and that the photoconductivity results from infrared, rather than visible, radiation.
31(1963); http://dx.doi.org/10.1119/1.1969138View Description Hide Description
The jump frequency of a diffusing atom in a crystal is examined from a dynamical point of view. Its motion is considered to be the superposition of many independent sine waves—the lattice vibrations. Whenever a critical displacement is reached, the atom “diffuses.” The probability of the waves adding up to produce this critical displacement of the atom is calculated on the basis of an elementary model. Temperature is brought in by assuming equipartition of energy among the lattice vibrations. This work is a simplified version of the dynamical theory of Rice [Phys. Rev. 112, 804 (1958)], the simplifications being such as to reduce greatly the mathematical complexities in order to bring out better the physical process. No new results are claimed, but it is believed that this work has heuristic and pedagogical value.
31(1963); http://dx.doi.org/10.1119/1.1969139View Description Hide Description
An account is given of the manner in which terms transform when a time-independent magnetic field is applied to a crystal structure containing a magnetic ion. The terms in question are those of the magnetic crystal-ion. The discussion is based on the von Neumann-Wigner theorem concerning the nonintersection of terms having equivalent transformation properties. An example is given which illustrates this theorem.
31(1963); http://dx.doi.org/10.1119/1.1969140View Description Hide Description
Maxwell's reasons for introducing displacment current are considered. His published works disclose no arguments based upon symmetry, but emphasis on the symmetry of Maxwell's equations with regard to electric and magnetic fields is found in Oliver Heaviside's work on electromagnetictheory.
31(1963); http://dx.doi.org/10.1119/1.1969141View Description Hide Description
Two undergraduatelaboratory experiments on the Hall effect are described in which the specimens are in the form of thin evaporated films. The first is concerned with the determination of the Hall coefficient and the mobility of conduction electrons in gold. The second describes the construction and the performance of magnetic fluxmeters made with bismuthfilms. Experimental data are given for a goldfilm 254 Å thick and for bismuthfilms ranging in thickness from 100 to 1430 Å.
31(1963); http://dx.doi.org/10.1119/1.1969142View Description Hide Description
A simple proof based on an elementary analysis of its eigenvalue problem is given of the reduction of the general element of the proper orthochronous Lorentz group to one of two possible standard forms. This represents the closest analog to Euler's theorem on rigid-body rotations.
31(1963); http://dx.doi.org/10.1119/1.1969143View Description Hide Description
The construction of a two-dimensional air table is described. This is an extention of the Neher-Leighton one-dimensional air trough to two dimension. The air cushion is provided by a perforated surface placed over an air-distribution manifold. The pucks consist of solid glass disks. A special wall keeps the energy loss from the system small. The conservation laws of linear and angular momentum can easily be studied, as can the general behavior of a two-dimensional gas.
31(1963); http://dx.doi.org/10.1119/1.1969144View Description Hide Description
It is shown, in contradiction to an argument recently proposed by J. Sokoloff, that the commonly used derivation of the Lorentz transformation, based on the requirement for invariance of the propagation law of a light wavefront, is indeed valid in one dimension as well as in two or three. The point of interest is the necessity to take due account of the isotropy condition in one dimension.
31(1963); http://dx.doi.org/10.1119/1.1969145View Description Hide Description
The electrostatic field, electromagnetic waves, electromagnetic induction, and the puremagnetic field are illustrated and explained in terms of a single pictorial representation of thegeneral electromagnetic field of a classical charged particle. The field of a charged particleis described by the orientation and density of a family of surfaces radially distributed aboutthe path of the particle in space-time. This description of the Maxwell field requires no referenceto any coordinate system or field components.