ISSN:0002-9505    

DOI:10.1119/1.19041

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18884

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

Public hunger for relativity and quantum mechanics is insatiable, and we should use it selectively but shamelessly to attract students, most of whom will not become physics majors, but all of whom can experience “deep physics.” Science, engineering, and mathematics students, indeed anyone comfortable with calculus, can now delve deeply into special and general relativity and quantum mechanics. Big chunks of general relativity require only calculus if one starts with the metric describing spacetime around Earth or black hole. Expressions for energy and angular momentum follow, along with orbit predictions for particles and light. Feynman’s Sum Over Paths quantum theory simply commands the electron:Explore all paths.Students can model this command with the computer, pointing and clicking to tell the electron which paths to explore; wave functions and bound states arise naturally. A second full-year course in physics covering special relativity, general relativity, and quantum mechanics would have wide appeal—and might also lead to significant advancements in upper-level courses for the physics major.

ISSN:0002-9505    

DOI:10.1119/1.18875

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

The Stern–Gerlach experiment was one of the early illustrative examples of the Bohr view of quantum mechanics. In the Bohr view, a measurement is an interaction between a quantum object and an apparatus which acts in a classical fashion. There are still open problems with this concept, many of which enter into the discussion of the original Stern–Gerlach measurement.

ISSN:0002-9505    

DOI:10.1119/1.18876

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

An experiment combining holography and musical acoustics is described. Structures of vibration modes of a bell are visualized by time-average holography under either acoustical or mechanical excitation. The vibration amplitude as measured by an accelerometer shows very good quantitative agreement with that determined from our holograms by fringe counting. An effect of degenerate level separation is shown in the mechanical case. It is argued that this experiment is not only very inexpensive for a physics laboratory already equipped for holography, but that it also strongly stimulates students to deepen their insight into a variety of different topics in applied physics.

ISSN:0002-9505    

DOI:10.1119/1.18877

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

Francois Arago brought the news of Oersted’s discovery of the effect of a current-carrying wire on a magnet to Paris on September 4, 1820. André-Marie Ampère and the team of Jean-Baptiste Biot and Félix Savart quickly set to work to establish a quantitative law for this effect. Their approaches were quite different. This paper describes the experiments of Biot and Savart and their results. It also briefly discusses the approach of André-Marie Ampère, who coined the name “electrodynamics” and whose fundamental formula gave the force between two infinitesimal current elements. Ampere’s formula fell into disuse after the advent of Maxwell’s field approach. Biot and Savart’s experimental law, in the modern form of the differential magnetic field due to a current element, became the standard starting point for calculating the magnetic field due to steady currents.

ISSN:0002-9505    

DOI:10.1119/1.18878

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

A general belief among members of the scientific community is that glass articles can be bent irreversibly and that they flow at ambient temperature. This myth is mostly based on widespread stories that stained-glass windows of medieval cathedrals are thicker in the lower parts. In this paper I estimate the time periods required for glass to flow and deform at ordinary temperatures, using calculated viscosity curves for several modern and ancient glass compositions. The conclusion is that window glasses may flow at ambient temperature only over incredibly long times, which exceed the limits of human history.

ISSN:0002-9505    

DOI:10.1119/1.19026

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

The meaning and scope of a recent type of uncertainty relation of a very general character are elucidated using the notions of time-indicating dynamical variables (clock variables) and place-indicating dynamical variables (position variables). It is shown that if the total energy (momentum) of a system is certain, all time-indicating (place-indicating) dynamical variables are completely uncertain. The quantum clock is discussed as an illustration of the energy–time uncertainty relation. The relations can be successfully applied to the thought experiments that Einstein introduced into his debate with Bohr about the uncertainty principle(s) and, in particular, to the famous photon-box experiment. It is shown that due to this general relation the photon box can never serve its purpose, independent of the details of the experiment.

ISSN:0002-9505    

DOI:10.1119/1.18880

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

An approximate method for the direct or near-field calculation of radiation reaction is introduced. The usual technique for the direct calculation requires determining the effect of the field produced by an extended source at a retarded time acting on the same extended source at the current time. The approximation consists of replacing the retarded source by a point source whose properties are determined by the radiation field. This approximation is applied to three examples: the average power radiated by a circular current loop, the radiation reaction torque acting on a rotating magnetic dipole, and the radiation reaction force exerted on a charged particle.

ISSN:0002-9505    

DOI:10.1119/1.18881

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

According to the general theory of relativity, kinetic energy contributes to gravitational mass. Surprisingly, the observational evidence for this prediction does not seem to be discussed in the literature. I reanalyze existing experimental data to test the equivalence principle for the kinetic energy of atomic electrons, and show that fairly strong limits on possible violations can be obtained. I discuss the relationship of this result to the occasional claim that “light falls with twice the acceleration of ordinary matter.”

ISSN:0002-9505    

DOI:10.1119/1.18885

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP