摘要:

The spreading or nonspreading of wave packets in one‐dimensional linear and quadratic potentials can readily be determined by solving Ehrenfest’s equations. The results for quadratic potentials can be understood in simple intuitive terms by using quantum distribution functions in phase space which, like classical distributions, rotate clocklike in time once per motional cycle. For more complicated situations, such as potentials with quantum energy spacings which are integral multiples of a basic unit, much can be learned instead by studying the quantum recurrence of their time‐dependent wave functions or probability densities.

ISSN:0002-9505    

DOI:10.1119/1.18177

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Static equilibrium conditions are applied to the case of moving a piece of furniture. Assume that two people are carrying a piece of furniture down a hill with a uniform speed. The load distribution on both people is found to be a function of the slope of the hill, the difference in the heights of the two people, the length of the furniture, and, more importantly, the force angle that the person at the upper end applied relative to a horizontal line. Some interesting features are revealed through this analysis. For example, contradictory to our common sense, the person at the lower end does not always carry more ‘‘weight.’’ This problem was found to be effective in helping students develop the static equilibrium concept.

ISSN:0002-9505    

DOI:10.1119/1.18178

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

We derive a useful expression for the time‐development operator for quantum wave functions, exp(−iĤt/ℏ), for the case of a particle subject to a constant force. We apply it, in both position and momentum space, to construct wave packets that exhibit uniform acceleration. We use these results to generate quantum wave packets corresponding to the motion of a charged particle in a uniform electric field in two different gauges, explicitly demonstrating the change in phase of the wave function under a gauge transformation. The more standard description of the time dependence of accelerating wave packets using the formalism of propagators is briefly reviewed in an Appendix for comparison.

ISSN:0002-9505    

DOI:10.1119/1.18179

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

An obstacle in the path of a water jet emerging from a tap gives rise to a stationary wave pattern upstream of the obstacle. In this paper, the wavelengths and the damping coefficients of these waves are calculated for various jet radii and velocities. The calculations indicate that the wavelength decreases and the damping coefficient increases with increasing jet velocity, in qualitative agreement with observations.

ISSN:0002-9505    

DOI:10.1119/1.18180

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The possibility of explaining time dilation as a dynamic cause‐and‐effect phenomenon is explored by calculating the rates of three elementary electromagnetic clocks in a stationary and in a moving reference frame. The operation of the clocks is based on the interaction between a field‐experiencing electric point charge and different field‐producing electric charge configurations. The calculations show that, when the clocks move, they run as predicted by the special relativity theory. The slowing down of the three moving clocks is due to a different electromagnetic field produced by the moving field‐producing charges (and hence due to a different force acting on the field‐experiencing charges) as well as due to a change of the effective mass of the moving field‐experiencing charges. Thus, for the clocks under consideration, time dilation can be considered a dynamic cause‐and‐effect phenomenon and not merely a kinematic effect, as time dilation is usually explained in conventional presentations of the special relativity theory.

ISSN:0002-9505    

DOI:10.1119/1.18181

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18223

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18238

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18170

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

ISSN:0002-9505    

DOI:10.1119/1.18239

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18240

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP