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Dec 1954

Volume 22, Issue 9, pp. 583-642

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Finding the External Force

Thomas D. Phillips

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 583

Online Publication Date: Jul 2005

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Ambiguity in the statement of Newton's first law of motion occurs in most introductory physics texts. This is due to vagueness or inconsistency in the use of the word body. To make the statement of the law plain in meaning three revised wordings are available. In the opinion of the writer the best solution is to substitute the phrase, the center of mass of any body in the place of the common phrase every body.

Topology of Steady Current Magnetic Fields

Keith Leon McDonald

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 586 | Cited 1 time

Online Publication Date: Jul 2005

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Textbooks often hold erroneously that the condition ∇⋅H = 0 implies that lines and tubes of force are closed. Examples are given in which the lines of force are not only unclosed, but also, the density of lines may be made infinite in a region where the field intensity is finite. If the steady electric current density is everywhere finite, the magnetic field has singularities only at discrete points, lines, or surfaces, where H = 0. In general, an infinity of lines of force may terminate on these points. Lines of force may have finite length, going from one singularity to another. A systematic analysis is made of the allowed distribution of singular points, and the linear fields in the neighborhoods of these points are classified. Certain types of singularities may appear in regions of finite current density, but cannot occur in regions free of current. Lines of force may form limit cycles.

Shock Waves in Gases

W. C. Griffith and Walker Bleakney

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 597 | Cited 4 times

Online Publication Date: Jul 2005

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This paper is in part a review but it also contains some original work. It deals with the manner in which shock waves are formed from finite compressions in gases and describes something of the structure of the shock front itself. The principal features of the behavior of shocks in reflection, refraction, and diffraction are discussed with particular attention given to anomalous observations and comparison with simple theories. Some results are given for shocks in real molecular gases showing relaxation effects. Quite a number of illustrations are included from the authors' own observations in the shock tube. The treatment is not exhaustive but covers many points likely to be of interest to teachers of physics.

Note on Perturbation Theory

Saul T. Epstein

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 613 | Cited 15 times

Online Publication Date: Jul 2005

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Perturbation theory is derived in such a way that the wave function renormalization terms appear automatically. The derivation is based on the Feynman theorem for the rate of change of an eigenvalue with respect to a parameter, and a corresponding theorem for the rate of change of an eigenfunction.

A Way of Representing the Motion of a Classical System as Being along a Geodesic in Space-Time

H. L. Armstrong

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 615

Online Publication Date: Jul 2005

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Ordinarily, the Jacobi formulation of classical mechanics describes a system by giving the path of a “system point” in “configuration space,” the path being a geodesic if a metric is suitably defined. Nothing is said, however, about the motion in time.
It is suggested here that, by adding a degree of freedom in uniform motion to serve as a clock, and identifying the time with the coordinate of that degree of freedom, the configuration space can be extended to a space-time, in which the motion is completely described, both in space and in time, as being along a geodesic. Also, by this representation, the idea of “absolute time” is made unnecessary.
A representation such as this is, of course, normal in relativistic theory, but its use here in nonrelativistic mechanics is believed to have some novelty.

Phase, Group, and Signal Velocity

J. Weber

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 618

Online Publication Date: Jul 2005

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Phase, group, and signal velocity are defined. Simple examples are given in which the phase and group velocities exceed the velocity of light, in which the phase velocity is a function of distance, and in which the group velocity is equal to the signal velocity.

Paper Representations of the Noncubic Crystal Classes

L. I. Schiff

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 621

Online Publication Date: Jul 2005

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It is shown that the full symmetries of twenty-seven of the thirty-two crystal classes, all except the five cubic classes, can be exhibited by suitably marked pieces of paper or cardboard. It is necessary to use both sides of the paper, and to exploit its small but finite thickness.

Teaching Transistor Physics

William J. Leivo

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 622

Online Publication Date: Jul 2005

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In June, 1952, the Bell Telephone Laboratories, Murray Hill, New Jersey, sponsored a summer school for teachers of transistor physics. During the sessions the basic ideas of semiconductors were studied, and a series of fundamental experiments was performed. At Carnegie Institute of Technology the student interest in these experiments has been very high and the results were so gratifying that we felt it would be most welcome if the Bell Telephone Laboratories made these experiments available to colleges which were not represented at the transistor sessions. This they have kindly agreed to do. A brief discussion of the experiments developed by the Bell Telephone Laboratories is given in this article.

Reproductions of Prints, Drawings, and Paintings of Interest in the History of Physics. 65. The Discovery of the Zeeman Effect

E. C. Watson

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 633

Online Publication Date: Jul 2005

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This article reproduces and interprets three stained glass windows that have been installed in the Kamerlingh-Onnes Laboratory at the University of Leiden to commemorate the discovery of the Zeeman effect.
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Encouraging Students to Choose Intelligently an Arbitrary Parameter in an Elementary Laboratory Experiment

F. H. Mitchell

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 636

Online Publication Date: Jul 2005

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Abstract Unavailable
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A Philosophy of Demonstration Experiments

Julius Sumner Miller

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 637 | Cited 1 time

Online Publication Date: Jul 2005

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Millikan Oil-Drop Experiment—A Demonstration Model

Arthur G. Rouse

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 637

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Terms of Statistical Mechanics

V. F. Lenzen

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 638

Online Publication Date: Jul 2005

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Terminology of Statistical Mechanics

D. ter Haar

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 638

Online Publication Date: Jul 2005

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Abstract Unavailable
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Training of College Physics Laboratory Assistants

C. J. Overbeck

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 639

Online Publication Date: Jul 2005

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Physics of Experimental Method

H. J. J. Braddick, Author and Otto Oldenberg, Reviewer

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 640

Online Publication Date: Jul 2005

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Elements of Statistical Mechanics

D. ter Haar, Author and William Band, Reviewer

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 641

Online Publication Date: Jul 2005

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Acoustics

T. M. Yarwood, Author and Robert W. Young, Reviewer

American Journal of Physics -- December 1954 -- Volume 22, Issue 9, pp. 642

Online Publication Date: Jul 2005

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Abstract Unavailable
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