ISSN:0002-9505    

DOI:10.1119/1.16803

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16804

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16805

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16806

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16807

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

This article shows how a simple Christmas ribbon can be used to demonstrate a relatively complex physical phenomenon: the conservation of helicity during magnetic reconnection. The physical term, helicity, and the process of magnetic reconnection will be introduced and explained in detail. The ‘‘helicity meter,’’ a very simple device that will help in the determination of the helicity of certain topological configurations, will also be introduced.

ISSN:0002-9505    

DOI:10.1119/1.16808

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

For a two‐level quantum mechanical system, pictorial descriptions of states, state vectors, phases, and their time evolution on the two‐ and three‐sphere are discussed, including adiabatic changes and Berry’s phase.

ISSN:0002-9505    

DOI:10.1119/1.16809

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

Three different methods for generating numerical solutions of Laplace’s equation are derived using a differential operator formalism for a Taylor series expansion of the electric potential about a point. The expansions are evaluated on three different two‐dimensional grids in thex‐yplane to yield algorithms good up to, but not including, fourth order. The accuracy and convergence of the algorithms are compared by applying them to a rectangular boundary value problem. Second, it is shown that the convergence criterion for numerical solutions can be interpreted as a charge density; and, therefore, the numerical solutions are, in fact, solutions of Poisson’s equation. Further, it is demonstrated that the numerical solutions of Laplace’s equation are bounded above and below by the solutions of Poisson’s equation corresponding to a maximum uniform charge density derived from the convergence criterion. For this reason, it is recommended that numerical solutions of Laplace’s equation should be accompanied by a statement of the maximum uniform charge density.

ISSN:0002-9505    

DOI:10.1119/1.16810

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

Ro/mer’s method for the determination of the speed of light, based on the observation of the immersions and emersions of Jupiter’s satellites, can be interpreted in the spirit of the Doppler effect. Although this statement appears to be plausible, textbooks very seldom adopt this point of view. Granted the tabular value of the satellite’s period, this interpretation permits one to determine the speed of light in about a week, as contrasted to half a year in the original method. It is suggested to include the measurement as a student experiment in the optics curriculum. Results of actual observations are given.

ISSN:0002-9505    

DOI:10.1119/1.16811

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

This paper seeks to promote a wider use of the two little‐known time‐dependent, generalized Coulomb and Biot–Savart laws in the form given by Jefimenko’s book. For some problems, these two time‐dependent laws giving the electromagnetic field from known distributions of charge and current densities without spatial differentiations provide a more convenient method of solution, but they are not well known, probably due to their difficult derivation. This paper gives an alternative derivation to these formulas using a novel ‘‘light cone transformation’’ that may be more appealing to some readers than the derivation given in the book by Jefimenko. The paper then shows that together with the law of conservation of charge these two laws can give back Maxwell’s system of four equations when the medium is infinite, homogeneous, linear, and isotropic; consequently, the time‐dependent, generalized Coulomb, Biot–Savart, and charge conservation laws can be used for such a case instead of Maxwell’s four equations. Three elegant examples, which have been traditionally solved in lengthy ways, or using the postulates of the special relativity theory, are then solved using these formulas: They are the examples of a differential antenna, of an electron in a uniform motion, and in an arbitrary motion (Feynman’s formulas). The examples also highlight the necessity of using Lienard–Wiechert’s formula in typical applications of these time‐dependent laws.

ISSN:0002-9505    

DOI:10.1119/1.16812

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP