摘要:

The scattering probabilityW(v,v′), associated with particles of massminteracting by means of hard elastic collisions with moving scatterers of massM, is obtained in terms of the corresponding scattering probability associated with scattering from rigid elastic scatterers. The collision term in the Boltzmann transport equation can then be written in a form which is convenient for handling both equilibrium and transport phenomena. The conditions of equilibrium are discussed. The approximate collision term for a distribution function of the formf(v) = f0(v) + vxg(v(is derived, and the results applied to the problem of the conductivity to microwaves of a slightly ionized gas.

ISSN:0002-9505    

DOI:10.1119/1.1934967

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

It is shown that a graphical method can provide a rapid analysis of parallel planes in various crystal structures. This method can be used to answer questions regarding relative distances between planes and whether planes with a given set of Miller indices are equivalent, as well as to determine the relative populations of each type of atom in nonequivalent planes. This in turn enables one to make some immediate inferences about x-ray scattering intensities for various orders of reflection without recourse to complicated mathematical analysis. The method involves a construction of a projectional diagram in accordance with some simple rules, which are illustrated with reference to a cubic unit cell forCaF2, and then generalized to crystal structures of any other type.

ISSN:0002-9505    

DOI:10.1119/1.1934968

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

The motion of a charged particle in the field of a magnetic monopole is calculated classically. The differential scattering cross section is obtained, and it is seen that in the limit of small interaction strength the cross section resembles the Rutherford cross section. A simple relativistic correction is discussed.

ISSN:0002-9505    

DOI:10.1119/1.1934969

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

When a small (<2.5 g) ball of silicone putty was put into a vibrating cylinder, it first bounced around like a rubber ball. After some time the motion produced by the random impacts caused the sphere to change to a torus, and ultimately it broke up into smaller “dog bone” shaped pieces. If the size of the initial sphere was increased to 4–5 g or more, the spherical shape remained stable for many hours. When the initial shape was changed from a sphere to a cube to a prism, the minimum critical size that would form a stable sphere increased from about 3 to 6 to 20 g, respectively. The formation of the torus is due to the combined effect of the spectrum of relaxation times of the material, the short time of impacts with the wall, and the tendency of a body in free flight to rotate around the axis having the highest moment of inertia.

ISSN:0002-9505    

DOI:10.1119/1.1934970

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

A number of different uses of the concept true are distinguished within physics in order to answer the questions: When is a physical law true? and When is a theory true? It is shown that a law cannot be tested as true or false independently of some theory. The concepts of true in physics are shown to be quite different from those of philosophy. The uses of true in physics make no reference to nature or the external world as is often held, nor do the changes in theories bring us progressively nearer to a correct picture of nature.

ISSN:0002-9505    

DOI:10.1119/1.1934971

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

A series of articles containing construction notes and drawings of apparatus for teaching undergraduate college physics will appear in theAmerican Journal of Physicsbeginning with this issue. The present paper reviews the origin and the objectives of the Apparatus Drawings Project.

ISSN:0002-9505    

DOI:10.1119/1.1934972

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

A spectrum tube for the Balmer series of hydrogen that is simple to construct, reliable, and has a useful life in excess of 1500 hours is described. The intensity of the atomic spectrum of hydrogen is more than adequate for visual work with a grating replica or prism, and under proper conditions would be sufficient for photographic use. The molecular spectrum of hydrogen is of negligible intensity when the tube is properly filled. Full information is given on the construction and filling of the tube.

ISSN:0002-9505    

DOI:10.1119/1.1934973

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

Our principal concern in the study of physics is: how does Nature behave? The answer is best gotten by finding the answers to an array of simpler fundamental questions.It is important, therefore, to know what questions to ask. This paper bears on several instructional points of view: (1) in the professor's narration there is too much communication of fact and too few of the right kinds of questions asked; (2) textbook problems do not cultivate the habit of asking questions; (3) there should be more general analytic exercises which permit the examination of limiting cases, for in limiting cases lies the heart of the inquiry; (4) demonstration experiments must be accompanied by appropriate questions. Illustrative examples point up the argument.

ISSN:0002-9505    

DOI:10.1119/1.1934974

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

This account of the early history of the infrared spectral region is concerned with tracing the growth in understanding of the nature and properties of this radiation from the time of its discovery by Herschel in 1800 up to the first part of the present century. After workers in the first half of the 19th century had demonstrated the fundamental similarity of infrared and visible radiation, investigators during the second half discovered the materials and evolved the techniques of measurement and control of infrared radiation which provide the foundation for the current extensive use of infrared equipment in research, industry, and ordnance.

ISSN:0002-9505    

DOI:10.1119/1.1934975

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

The paper first discusses the significance of the meaning of space-time coordinates as attached to “events” in the Lorentzian transformation. Restricted relativity involves two distinct parts: A—the invariance of theformsof the laws under the transformation: B—the hypothesis that similar experiments performed in relatively moving framesSandS′ give identical results. The test of A is a matter of pen and paper. B involves the hypothesis that the instruments are such that the actual measurements of space-time coordinates of events shall be related, for the two systems, by the transformation. Only by the postulation of a theory such as the quantum theory, but one relativistically invariant in sense A, can one understand the relationship between the instruments, whether the said instruments be constructed by independent observers inSandS′ from the material around them, or whether the observer inS′ acquires his instruments fromSby setting them in motion. The second method of acquiring the instruments will not, in all cases, yield measurements related by the transformation. Thus, if we start with a system ofisolatedclocks which have been synchronized inSaccording to Einstein's principle, and if we transfer them toS′, their “rates” (in a suitably defined manner) may be expected to alter in accordance with the transformation. However, it will remain for the observer inS′ to synchronize the clocks in that new frame, having adjusted the time origin of one of them.

ISSN:0002-9505    

DOI:10.1119/1.1934976

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP