摘要:

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 wordbody. 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, thecenter of mass of any bodyin the place of the common phraseevery body.

ISSN:0002-9505    

DOI:10.1119/1.1933853

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

Textbooks often hold erroneously that the condition∇·H = 0implies 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, whereH = 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.

ISSN:0002-9505    

DOI:10.1119/1.1933854

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933855

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933856

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933857

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933858

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933859

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933860

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

摘要:

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.

ISSN:0002-9505    

DOI:10.1119/1.1933861

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.1933862

出版商:American Association of Physics Teachers    

年代:1954

数据来源: AIP