摘要:

This article is the text of a talk given by the author at the 1956 Summer Meeting of the AAPT. The audience included not only members of the Association plus other physicists, but also, as expected, a number of wives and even some children. For this reason the subject, “Weighing Atoms,” was presented at an elementary level in the hope both of instructing the lay element in the audience and of amusing the professional physicists who were present.

ISSN:0002-9505    

DOI:10.1119/1.1934538

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

The problem of reconciling the irreversibility of thermodynamics with the completely reversible mechanics of the ultimate constituents of the thermodynamical system is examined from an operational viewpoint. The informational nature of entropy is demonstrated, and the famous paradoxes of statistical mechanics, due to Loschmidt and Zermelo, are resolved with its aid. Spin echo experiments are shown to realize the conditions of Loschmidt's reflection paradox, and used to illustrate how reversibility occurs only with perfect “memory” or information storage, while “forgetting” or loss of information implies irreversibility.

ISSN:0002-9505    

DOI:10.1119/1.1934539

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

The meaning of Liouville's theorem on the flow of points in phase space is discussed. The intensity for particles or for radiation is defined in the most general case. It is shown that the familiar theorem which states that an optical instrument cannot change the brightness of any object which it images is a special case of Liouville's theorem. The generalization of this result to classical particle- and radiation-handling systems of many kinds is discussed. The result holds even for situations in which the fields or refractive index distributions are arbitrarily varying in time, though in such situations the trajectories of “constant brightness” may move around by bending and distorting so that a stationary observer may thereby see some changes. The problem of point sources is considered. Simple examples of phase space motions are exhibited.

ISSN:0002-9505    

DOI:10.1119/1.1934540

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

Astronomical studies of the life histories of the stars lead to speculation about our own future.

ISSN:0002-9505    

DOI:10.1119/1.1934541

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

An experimental apparatus for measuring thermal conductivity of solid materials is described which is analogous to the Wheatstone bridge for measuring electrical resistance.

ISSN:0002-9505    

DOI:10.1119/1.1934542

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

This is a study of the motions of a particle subject to the restoring force exerted by a linear spring, under the assumption that the mass depends upon the speed according to the formula given by the theory of special relativity.

ISSN:0002-9505    

DOI:10.1119/1.1934543

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

A discussion of observations in magnetic resonance experiments and their relations to the processes involved involves consideration of the populations of magnetic states. By adding a population coordinate to an energy diagram a representation is obtained by which the time change of state population can be illustrated. Application is made to effects of the Overhauser type in solids, especially in semiconductors.

ISSN:0002-9505    

DOI:10.1119/1.1934544

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

The distribution of free electrical charges transferred to cloud droplets by ionic diffusion provides an illuminating example of a simple statistical process. Tables are constructed from first principles, shown to agree with successive terms of the binomial point equation of statistics, and applied to the initial stages of droplet electrification. The final equilibrium distribution, described by the basic electrification equation for aerosols, corresponds to an equipartition between the electrostatic energy of the droplets and their thermal kinetic energy.

ISSN:0002-9505    

DOI:10.1119/1.1934545

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

A survey is given of interpretations of nuclear properties based on the two differing models of nuclear structure, the liquid-drop model and the shell model. These can be considered to be two approximate representations of a structure that is is more complex than either. A more comprehensive model is discussed and shown to facilitate interpretation and correlation of the ellipticities of some nuclei indicated by the hyperfine structure of spectra, of rotational gamma-ray spectra, and of the process of Coulomb excitation.

ISSN:0002-9505    

DOI:10.1119/1.1934546

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP

摘要:

There is no ambiguity about the relationship between time and motion, either in terms of experiments with rapidly moving mesons or canal rays, or in terms of general relativity theory. But contradictory resultsareobtained when it is attempted to make computations using only the special relativity theory. A number of opinions to the contrary have recently found their way into print.

ISSN:0002-9505    

DOI:10.1119/1.1934547

出版商:American Association of Physics Teachers    

年代:1957

数据来源: AIP