ISSN:0002-9505    

DOI:10.1119/1.17889

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17858

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Once again, on behalf of all of our authors and readers, we want to express our gratitude to AJP’s reviewers. During the calendar year 1994, the 592 reviewers listed below contributed one or more (in some cases,manymore) referee reports on manuscripts submitted to this Journal. We all owe an enormous debt to their expertise and dedication. Don S. Lemons,AssistantEditorRobert H. Romer,Editor

ISSN:0002-9505    

DOI:10.1119/1.17859

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17860

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

An account is given of the instruction of university‐level introductory physics courses according to an educational framework in which (1) curiosity‐driven inquiry is recognized as an essential activity of both science and science teaching; (2) the principal role of the instructor is to provide students the incentive to learn science through their pursuit of personally meaningful questions; (3) the commission of errors is regarded as a natural concomitant to learning and is not penalized; (4) emphasis is placed on laboratory investigations that foster minimally restrictive free exploration rather than prescriptive adherence to formal procedure; (5) research skills are developed through out‐of‐class projects that involve literature search, experiment, and the modeling of real‐world physical phenomena: (6) the precise and articulate use of language is regarded as seminal to communication in science (as it is in the humanities) and is promoted through activities that help develop written and oral language skills; (7) the evaluation of student performance is based on a portfolio of accomplished work rather than on the outcome of formal testing.

ISSN:0002-9505    

DOI:10.1119/1.18080

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

The matching conditions that describe the behavior of electromagnetic fields at an interface between two media are usually obtained from the integral form of Maxwell’s equations. There are pedagogical benefits to augmenting this approach with one that begins with the differential form of Maxwell’s equations and employs unit step functions and the Dirac delta function. With such an approach, it is possible to avoid the use of the rectangles and pillboxes introduced in the standard textbook derivation, make explicit in the matching conditions their dependence on the shape of nonplanar or irregular interfaces, and reveal the connection between the matching conditions and the permittivity‐gradient (∇ε) terms that appear in the wave equations for the electric and magnetic fields.

ISSN:0002-9505    

DOI:10.1119/1.17861

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

In a typical dipole decay, the induction magnetic field and the radiation magnetic field are in opposing directions. The former is dominant close to the decay, and the latter is dominant far away. Thus, there exists a surface on which these two components cancel each other, so that the magnetic field reverses direction. Because the magnetic field changes direction, so also will the Poynting vector field, provided the electric field is reasonably well behaved. This defines a ‘‘causal surface,’’ within which electromagnetic energy will collapse, and outside which the electromagnetic energy will radiate away. I present a simple example, the decay of a point electric dipole, to argue that the radiated energy comes, not necessarily from the accelerating charges themselves, but from the energy stored in the far field.

ISSN:0002-9505    

DOI:10.1119/1.17862

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Symmetries play an important role in physics. In this article, we examine the relationship between magnetism and mirror symmetry. The reflection properties of the vector potentialA(t) and the magnetic inductionB(t) are obtained, and these properties are used to analyze some simple circuits.

ISSN:0002-9505    

DOI:10.1119/1.17863

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

The fall of a body through a planetary atmosphere is analyzed in a relatively simple, essentially analytic, manner, emphasis being placed on the physical processes involved.

ISSN:0002-9505    

DOI:10.1119/1.17864

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

The deflection of light by a gravitational field is an important prediction of general relativity. It is thus an interesting problem to illustrate the deflection by simulating the appearance of astronomical objects as seen through a gravitational field. To do this we have constructed plastic lenses to simulate the gravitational deflection of light for three cases: a point mass, a sphere of constant density, and an isothermal gas sphere. In this paper we discuss the calculation of the deflection for any distribution of mass, the shape of general simulation lenses, and the construction of plastic simulation lenses. To illustrate the results we present photos of a grid, a dark spot, and a field of stars and galaxies seen through the lenses. The photos clearly display the distortion of images, Einstein rings and arcs, and brightness intensification.

ISSN:0002-9505    

DOI:10.1119/1.17865

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP