摘要:

I consider the dynamics of a harmonic oscillator when its (circular) frequency ω is suddenly changed by a given factor λ. This exactly solvable time‐dependent system can be analyzed by using the basic tools of quantum mechanics and provides a simple illustration of their mutual relations and usefulness.

ISSN:0002-9505    

DOI:10.1119/1.18049

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

A few examples of systems in thermodynamic equilibrium are cited in the classic text of Lewis and Randall [Thermodynamics(McGraw‐Hill, New York, 1960)] which are problematic in that classical thermodynamics predicts the presence of a very small fraction of a single atom in a given form, e.g., tungsten vapor present in equilibrium with solid at 100 °C (p≂10−105atmosphere). Lewis and Randall state, however, that the vapor pressure of a normal system, e.g., water at room temperature and that of tungsten at 100 °C, can be used ‘‘with the same sense of security.’’ They do not elaborate further. The problem is analyzed from first principles and it is pointed out that the apparent incongruity in having a fractional atom is removed in the density matrix description of the equilibrium state. A description of the equilibrium state that avoids the concept of a ‘‘fractional atom’’ has to identify the equilibrium property as a time average. The shortcoming of such a description is pointed out.

ISSN:0002-9505    

DOI:10.1119/1.18050

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

We present a physics experiment, in which laser‐Doppler velocimetry is used to make first‐year university physics students realize that the idealized solutions offered by standard text books seldom are applicable without corrections, which often are numerical. This is demonstrated by carefully measuring and calculating the flow profile in a rectangular pipe.

ISSN:0002-9505    

DOI:10.1119/1.18051

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Nonlinear mixing between the longitudinal modes of multimode laser pulses is used to illustrate the effects of nonlinear crosstalk in multichannel communication systems. The results of the experiments are compared with a simple theoretical model that was described in a recent article. The article concludes with suggestions for experiments in nonlinear fiber optics for undergraduate and masters students.

ISSN:0002-9505    

DOI:10.1119/1.18053

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

A recent suggestion has been made that the hydrogen bound state spectrum should not depend on the number of spatial dimensions. It is pointed out here that the uncertainty principle implies that such differences must exist and that a perturbation expansion in the dimensionality parameter yields a precise quantitative confirmation of the effect.

ISSN:0002-9505    

DOI:10.1119/1.18054

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18025

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18026

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18027

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

ISSN:0002-9505    

DOI:10.1119/1.17995

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17996

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP