ISSN:0002-9505    

DOI:10.1119/1.16796

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16774

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16777

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

An experiment to study the effect of relativistic time dilation on secondary muon fluxes observed at different altitudes is described in this article. Muons, produced as secondary particles from the interaction of primary cosmic rays with the upper atmosphere, form a natural and abundant source of subatomic ‘‘clocks’’ moving at very high speeds. The measured muon flux on a mountain relative to that measured at sea level can be compared to predictions from calculations that take into account the relativistic time dilation in the muon frame. Situations under which such an experiment can be successfully performed are explored with a day‐long field trip to a nearby mountain. This experiment has been developed at Smith College as a module in the Five College cooperative undergraduate advanced laboratory course (other participating institutions are Amherst College, Mount Holyoke College, and the University of Massachusetts).

ISSN:0002-9505    

DOI:10.1119/1.16841

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

It is shown that the standard exposition of the two‐slit diffraction experiment is incorrect because it treats the interference as arising from the photon wave function ψ, whereas the interference is really between coherent states of the field, which do not correspond to single‐photon states. Several other misconceptions are pointed out.

ISSN:0002-9505    

DOI:10.1119/1.16778

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

During the 1930s, cosmic rays were the most important source of data on the high‐energy behavior of both quantum electrodynamics and nuclear forces. In the period 1934–1938, with which this article is concerned, the dominant fundamental theory of nuclear forces was that of the Fermi field. In sorting out the various cosmic‐ray phenomena in the atmosphere, it was found that the less penetrating components were associated with electromagnetic cascade showers, and that the more penetrating component contained a new ‘‘elementary’’ particle, the mesotron. However, there remained puzzling features of the cosmic rays that left adequate room for other interpretations.

ISSN:0002-9505    

DOI:10.1119/1.16779

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

A program of proofs is outlined to show how the linear structure of quantum mechanics can be derived from basic principles. For the dynamics part, three alternatives are reviewed briefly. They include the Kadison theorem for evolution of density matrices and the Segal–Simon theorem for evolution of observables in the Heisenberg picture. The focus is on Wigner’s theorem that gives linear operators for evolution of state vectors. New insights are described that motivate the key assumption about probabilities in that theorem. One is that it is implied by the second law of thermodynamics. Another is that it follows from assumptions that evolution in time preserves mixtures of states and preserves probabilities for what is in the mixture.

ISSN:0002-9505    

DOI:10.1119/1.16780

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

The Johnson–Nyquist formula for spontaneous voltage fluctuations across a conductor is rederived for metals at a tutorial level within the framework of the free‐electron approximation. The spontaneous current fluctuations are linked directly to the occupancy fluctuations in the Fermi–Dirac distribution function for the conduction electrons and to the electron‐scattering processes that are responsible for the electrical resistivity. It is also shown that an externally applied Ohmic current through a metal does not affect its thermal noise. The quantum limit of thermal noise is discussed briefly.

ISSN:0002-9505    

DOI:10.1119/1.16781

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

A freely rotating magnet placed above a solenoid and between a set of Helmholtz coils is used to examine properties of a nonlinear system. Accurate measurements of the angular velocity are made with a photogate timing device. The period‐doubling route to chaos, multiple periodicities, and the behavior of transient motion are observed and measured.

ISSN:0002-9505    

DOI:10.1119/1.16782

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

The dripping water faucet is a simple system which is shown in this article to be rich in examples of chaotic behavior. Data were taken for a wide range of drip rates for two different faucet nozzles and plotted as discrete time maps. Different routes to chaos, bifurcation and intermittency, are demonstrated for the different nozzles. Examples of period‐1, ‐2, ‐3, and ‐4 attractors, as well as strange attractors, are presented and correlated to the formation of drops leaving the faucet.

ISSN:0002-9505    

DOI:10.1119/1.16783

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP