ISSN:0002-9505    

DOI:10.1119/1.16886

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16889

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16890

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

When observing a distant point source of light through a water droplet adhering to a pane of glass near one’s eye or the scattering of light from raindrops, one often sees optical caustics. In this paper, diffraction integrals are used to investigate these caustics. The caustic shapes are related to divergences in the stationary phase method for approximating the diffraction integrals. These divergences correspond to the coalescing of two or more geometrical light rays in ray optics or the coalescing of two or more regions of stationary phase in wave optics. The number of coalescing light rays is related to a polynomial approximation of the phase function in the diffraction integral. Also, the relation between the shape of the resulting caustic and the elementary caustic forms of the catastrophe optics classification scheme is described.

ISSN:0002-9505    

DOI:10.1119/1.16891

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

A model on the educational level is described to estimate effective future atmospheric CO2concentrations. The effects of chlorofluorocarbon and methane emission and deforestation are taken into account. The influence of different emission scenarios on the time evolution of greenhouse‐gas concentration are illustrated. Future global energy policies are discussed both under the aspects of rising world population and the reduction in global CO2emissions. The model can be handled on a PC or even on a pocket calculator.

ISSN:0002-9505    

DOI:10.1119/1.16892

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

The theoretical minimum for engine power rating required to accelerate a vehicle of massMto velocityVin timeTis shown to result from acceleration at constant maximum power. Because actual conditions do not allow infinite starting acceleration, the power per unit mass to provide optimum feasible acceleration with minimum engine power rating is given byPopt/M=a2maxTc, whereamaxis the maximum starting acceleration andTcis the crossover time from maximum acceleration to the curve of acceleration at constant maximum power. Comparison with analysis of performance data for 18 automobiles reveals that 17 achieve near‐optimum power usage.

ISSN:0002-9505    

DOI:10.1119/1.16893

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

A simple undergraduate laboratory experiment on the determination of Debye temperatures of solids is described. A sample of the solid is immersed in liquid nitrogen; from the mass of nitrogen boiled off in cooling the solid, the change in its internal energy is determined. The quantum corrections to the classical law of Dulong and Petit are calculated and the Debye temperature is obtained using a simple graphical technique.

ISSN:0002-9505    

DOI:10.1119/1.16894

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

The occurrence in Fourier series of an overshoot effect near function discontinuities, called the Gibbs phenomenon, is discussed from a pedagogical viewpoint. The reader is led along a path to discover why the phenomenon depends only upon the existence of the discontinuity, but not on other properties of the function that is Fourier analyzed.

ISSN:0002-9505    

DOI:10.1119/1.16895

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

A simple intermediate‐level mechanical nonlinear oscillator experiment is described which is used both as a lecture demonstration and as the basis for senior thesis research. Its special features are that the experimenter can easily control the degree of nonlinearity, that it readily exhibits the jump phenomenon, and that it can be modeled by the Duffing oscillator.

ISSN:0002-9505    

DOI:10.1119/1.16896

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

A simple quantum‐mechanical model consisting of a two‐level system coupled to a continuum, where the interaction can be varied from perturbative to strong, is examined for what can be learned about quantum mechanical decay using elementary methods. The decay spectrum and time dependence of the amplitudes can be calculated in this model, without resorting to perturbation theory. The spectrum is not precisely Lorentzian nor is the decay precisely exponential, features that appear to be shared by all quantum‐mechanical models of decaying systems. The conditions for exponential decay and some of the reasons for deviation from this at both short and long times are discussed.

ISSN:0002-9505    

DOI:10.1119/1.16897

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP