摘要:

Gravitational lensing is now regularly observed by astrophysicists, including the lensing of distant quasars by galaxies, and the lensing of stars in the galactic nucleus and in the Larger Magellanic Cloud by more nearby stars. The lensing is readily understood with the help of Fermat’s principle of stationary time to find the paths of light rays. Conventional discussions of Fermat’s principle in introductory physics and optics courses may easily be extended to include gravitational lensing, to show for example that even the simplest gravitational lens can produce multiple images of the same source.

ISSN:0002-9505    

DOI:10.1119/1.18291

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

During two academic years (1991–1992, 1992–1993), four new model curricula for the college‐level, calculus‐based introductory physics course were tested. A total of nine colleges and universities around the country participated in this test. This paper provides an overview of the evaluation process. The evaluation was independent—that is, it was not linked to the model developers or to the sites, nor was it directly implemented by the group that sponsored the project, the Introductory University Physics Project. At each site, we set out to study both ‘‘model’’ and ‘‘comparison’’ sections of the introductory physics course. There was a pre‐ and post‐test, and some limited use of in‐class questionnaires. Faculty members and roughly 10% of the students were asked to keep journals. Each test site was visited by an evaluator at least twice during each academic year. This paper provides some of the background necessary to assess the results of the IUPP evaluation. Some evaluation results from the 1991–1992 field tests are included in the following paper [R. Di Stefano, Am. J. Phys.64(1), 58–68 (1996)]. The main body of our results, including those focusing on the 1992–1993 trials, will be presented in later papers.

ISSN:0002-9505    

DOI:10.1119/1.18292

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The methods of analysis that were applied to the information gathered during the 1991–1992 field tests of the Introductory University Physics Project are demonstrated through the study of two specific questions. The first question addresses the effectiveness of in‐class demonstrations as an aid to learning. The relative importance of demonstrations, a feature relevant to most implementations of introductory science courses, emerged from comments contributed by students in both comparison and model courses. The second question is about the effectiveness of teaching and learning an area of physics (such as mechanics) through the use of an overarching context (such as ‘‘Interplanetary Travel’’). This question was inspired by the test of a specific model,PhysicsinContext.

ISSN:0002-9505    

DOI:10.1119/1.18293

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The analogy between the calculation of a two‐dimensional electrostatic field and that of a two‐dimensional magnetostatic field is exposed and yields a new theorem.

ISSN:0002-9505    

DOI:10.1119/1.18294

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A sodium iodide crystal connected to a multichannel pulse height analyzer card in a microcomputer is used to detect and analyze the progeny of radon gas present in the ambient air of several buildings. Relative levels are obtained in three buildings and an attempt is made at calculating absolute levels.

ISSN:0002-9505    

DOI:10.1119/1.18295

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

We outline an easily reproduced experiment that allows the student to investigate the intensity and phase structure of transverse laser modes. In addition to discussing the usual Hermite–Gaussian laser modes we detail how Laguerre–Gaussian laser modes can be obtained by the direct conversion of the Hermite–Gaussian output. A Mach–Zehnder interferometer allows the phase structure of the Laguerre–Gaussian modes to be compared with the phase structure of a plane wave with the same frequency. The resulting interference patterns clearly illustrate the azimuthal phase dependence of the Laguerre–Gaussian modes, which is the origin of the orbital angular momentum associated with each of them.

ISSN:0002-9505    

DOI:10.1119/1.18283

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The torque‐free rotation of a solid body is unstable about the axis with the intermediate principal moment of inertia. Such an instability can be shown with a simple experiment using a ruler. In this work, the equations of Euler are integrated and the orientation of the ruler, referred to the laboratory reference frame, determined as a function of time. This allows a beautiful comparison between the observed rotation of the ruler and the theory behind it.

ISSN:0002-9505    

DOI:10.1119/1.18296

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The combinatorial solution of finding the number of ways of distributingnparticles intogdistinguishable groups such that no group contains fewer thanqobjects or more thanq+aobjects is used to obtain the mean occupation number of noninteracting paraparticles in degenerate energy levels. It is shown that the donor electrons in an impurity level of a semiconductor behave as paraparticles under constraints, called slave paraparticles.

ISSN:0002-9505    

DOI:10.1119/1.18297

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18298

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18471

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP