ISSN:0002-9505    

DOI:10.1119/1.17559

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

This Resource Letter provides a guide to the literature on the possibility of a human‐induced climate change—a global warming. Journal articles and books are cited for the following topics: the Greenhouse Effect, sources of infrared‐trapping gases, climate models and their uncertainties, verification of climate models, past climate changes, and economics, ethics, and politics of policy responses to climate change. [The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field. The letter I, for intermediate level, indicates material of somewhat more specialized nature, and the letter A indicates rather specialized or advanced material.]

ISSN:0002-9505    

DOI:10.1119/1.17560

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

We introduce a simplified model of a ‘‘spherical battery’’ embedded within an infinite conducting medium, wherein the source of emf is taken to be a uniform vertical force per unit chargeF, of nonelectrical nature. This model can be solved analytically for the surface charge distribution, the electric field, the electric current density, the magnetic field, the Poynting vector, and the angular momentum density. Through the net current and net power loss, a ‘‘lumped’’ resistance can be defined, and from the net current and the lumped resistance a lumped emf can be defined. This example explicitly illustrates that the surface charge on a battery causes it, at a distance, to behave like an electric dipole. It also provides an explicit example where the nonelectrical ‘‘field’’ of the battery acts only within the battery, whereas the electrostatic field of the surface charge acts both within and outside of the battery. A spherical inclusion within a material with otherwise uniform current flow is also analyzed to obtain the electric field, current density, and magnetic field. Additional geometries with current flow and surface charge, both with and without batteries, for which there exist analytic but sometimes complex solutions, are discussed. Following a discussion of voltaic cells, it is pointed out that in real voltaic cells the emf occurs at the electrode–electrolyte interface rather than throughout the volume. From that we propose a more realistic but less tractable model for a spherical battery, in which the emf acts only within two hemispherical shells.

ISSN:0002-9505    

DOI:10.1119/1.17743

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Traditional textbook presentations of Fraunhofer interference and diffraction are usually limited to a few discrete examples of one, two, and sometimes more sources, in which the analysis yields graphs of intensity versus distanceyon a screen that is at a large distanceDin thexdirection from the sources. This paper presents two separate sets of graphical representations that can assist students and teachers in improving their understanding of the Fraunhofer phenomena. The polar intensity plots stress the angular nature of the interference phenomena, and stress the fact that the phenomena need not be limited to a narrow angular range around the forward direction. The three‐dimensional plots illustrate the unity of diffraction and interference by examining the patterns when one makes a continuous variation of the geometrical parameters that characterize the sources.

ISSN:0002-9505    

DOI:10.1119/1.17561

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

In the context of classical vector and tensor fields, the problem of consistently using delta functions to represent point sources is addressed. Specifically, a general expression for the gradient of a common term arising in point‐source tensor fields is presented. It is shown that the differential product rule fails for terms containing the delta function.

ISSN:0002-9505    

DOI:10.1119/1.17562

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

We consider the problem of deriving the appropriate modification of the standard Maxwell–Boltzmann, Fermi–Dirac, and Bose–Einstein distributions for the situation where the number of systems is not necessarily very large and thus the usual derivations break down. We obtain for each case a modified formula which yields only integer values for the relevant occupation number and which reduces to the standard result in the limit of large numbers.  

ISSN:0002-9505    

DOI:10.1119/1.17563

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Motivated by the work of Berry and Balazs and Greenberger on the 1‐D Schrödinger equation, we have investigated a class of nonspreading solutions to the 3‐D Schrödinger equation involving accelerating Airy envelopes. These solutions are characterized by an asymmetric structure, in contrast to recently derived spherically symmetric packets moving with constant velocities. The field of a characteristic Airy packet extends in an oscillatory fashion behind its peak amplitude, while it quickly disappears in front of the packet’s center. A particle modeled by such a packet seems to leave a wake of its field behind as it accelerates in a certain direction. On the other hand, a wave packet moving with a constant velocity has a field which is symmetrically distributed in all directions. Our work on Airy‐type solutions to the 3‐D Schrödinger equation has led us also to analogous solutions for the 3‐D scalar wave equation.

ISSN:0002-9505    

DOI:10.1119/1.17510

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Colliding steel rods, unlike colliding steel balls, can lose kinetic energy during collisions. The kinetic energy lost appears as stress (vibrational) energy in the rods: We describe apparatus suitable for lecture demonstrations and laboratory investigations of such collisions. We explain how colliding rods interact. The reasons why steel balls collide elastically remain mysterious.

ISSN:0002-9505    

DOI:10.1119/1.17511

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Jefimenko’s formulas for the time‐dependent electric and magnetic fields are generalized to include magnetic monopoles. To illustrate this generalization of Jefimenko’s formulas, the electric and magnetic fields of an arbitrarily moving dual‐charged particle, i.e., one containing both electric and magnetic charge, are obtained in the Heaviside–Feynman form as well as in the Liénard–Wiechert form. These fields are shown to be perpendicular to one another in the radiation zone but not in the near‐field zone.

ISSN:0002-9505    

DOI:10.1119/1.17512

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

The relativistic extension of one‐dimensional simple harmonic motion is developed in the Lagrangian formalism. The relativistic equations of motion are derived and solved analytically. The motion with respect to proper time is analyzed in terms of an effective potential energy. While the motion remains bounded and periodic, the effect of time dilation along the world line is to cause it to become anharmonic with the period increasing with amplitude and the curvature concentrated at the turning points.

ISSN:0002-9505    

DOI:10.1119/1.17513

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP