ISSN:0002-9505    

DOI:10.1119/1.16418

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16419

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16504

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A new method for calculating electric and magnetic forces is presented. The method makes it possible to calculate forces directly from scalar and vector potentials rather than from field vectors. Several new force equations are derived. They are grouped in four categories: equations for calculating electric forces from electric scalar potentials; equations for calculating electric forces from electric vector potentials; equations for calculating magnetic forces from magnetic vector potentials; and equations for calculating magnetic forces from magnetic scalar potentials. Since the potentials are usually easier to compute than the corresponding fields, the new equations provide an effective alternative to the previously available techniques for force calculations. From the theoretical point of view, these equations reveal a physical significance of electric and magnetic potentials not heretofore apparent and provide a new insight into the nature of electric and magnetic forces. Illustrative examples on the use of the equations are given.

ISSN:0002-9505    

DOI:10.1119/1.16420

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A rotating U‐tube experiment is described in which the axis of rotation lies between a vertical arm and the axis of symmetry of the tube. As the rotational frequency is slowly varied, the equilibrium position of the liquid in the tube can abruptly change, resulting in a hysteresis loop. The effect is not due to friction, which causes a much smaller amount of hysteresis. The data agree well with the theory.

ISSN:0002-9505    

DOI:10.1119/1.16421

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The necessary attribution of linear and angular momenta to the electromagnetic field, even in quasistatic situations, is illustrated by discussing the dynamical conservation laws of an interacting system composed of two point charges and a magnetic dipole. The evaluation of the trajectories gives an interesting example for numerical computation.

ISSN:0002-9505    

DOI:10.1119/1.16422

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A bare multipole potential Φ(r)=(A/rl+1)Pl(cos θ), concentric with a spherical cavity embedded within a dielectric, has its potential within the dielectric changed, not by the factor ε−1, but rather by the factorF(l)=(2l+1)/[l+(l+1)ε]. Moreover, a multipole source potential in the dielectric Φ(r)=(Arl)Pl(cos θ) has its potential within a concentric spherical cavity changed by a factor εF(l). The result is that the interaction between two multipoles in widely separated cavities is modified by a factor ε−1times a factor εF(l) for each multipole. By decomposing the bare potential of a point monopole source into its cavity multipole components, screening each component separately, and then resumming, it is shown why the method of images works both for point charges with semi‐infinite dielectrics and for line charges with dielectric circular cylinders—butnotfor point changes with dielectric spheres.

ISSN:0002-9505    

DOI:10.1119/1.16423

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A fast and inexpensive method for making accurate determinations of transition temperatures above 77 K in superconducting oxides is presented. The technique is based upon cooling in liquid nitrogen, then warming the sample in the vapors above the liquid level inside a standard glass or stainless steel vacuum bottle. Proper sample support and placement of the thermocouple, key elements in this technique, are discussed. Once pads have been placed on the sample,Tccan be determined, to an accuracy of ±1 K, within 15 min. Due to its speed, accuracy, and low cost, this technique is well suited for application in an advanced undergraduate laboratory experiment.

ISSN:0002-9505    

DOI:10.1119/1.16424

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The theory describing the surface impedance of a material is developed for normal conductors and high‐critical‐temperature superconductors. The discussion is extended to treat the nonlocal‐field case, not usually considered in elementary approaches. A general solution to the field equation, appropriate when the charge carriers are specularly reflected from the conductor surface, is developed, and the result for the more complex case of diffuse scattering is given.

ISSN:0002-9505    

DOI:10.1119/1.16425

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

It is argued that nonrelativistic quantum mechanics does not in all respects behave as a fully Galilean invariant theory. The difference is empirically significant, as is illustrated by the Sagnac effect. The conclusion of this article sheds some new light on a recent discussion concerning the status of de Broglie’s theory of matter waves.

ISSN:0002-9505    

DOI:10.1119/1.16426

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP