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Sep 1997

Volume 65, Issue 9, pp. 813-934

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Guest Comment: Research versus teaching—An ethical dilemma for the academic physicist

Alvin M. Saperstein

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 813

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01.50.-i Educational aids
01.75.+m Science and society
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American Association of Physics Teachers 1997 Oersted Medalist: Daniel Kleppner

Karen L. Johnston

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 815

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Abstract Unavailable
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01.10.Cr Announcements, news, and awards

“The Cat and the Moon: Chaos and High Precision:” Daniel Kleppner’s acceptance speech for the 1997 Oersted Medal presented by the American Association of Physics Teachers, 7 January 1997

Daniel Kleppner

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 816

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Abstract Unavailable
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01.10.Cr Announcements, news, and awards
01.50.-i Educational aids
05.45.-a Nonlinear dynamics and chaos
03.65.-w Quantum mechanics
06.20.Dk Measurement and error theory
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Resource Letter: ND-1: Nonlinear Dynamics

Robert C. Hilborn and Nicholas B. Tufillaro

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 822 | Cited 7 times

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This Resource Letter provides an introductory guide to the literature on nonlinear dynamics. Journal articles and books are cited for the following topics: general aspects of nonlinear dynamics and applications of nonlinear dynamics to various fields of physics, other sciences, and a few areas outside the sciences. Software and Internet resources are given also. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
01.30.Tt Bibliographies
05.45.-a Nonlinear dynamics and chaos

Classical antiparticles

John P. Costella, Bruce H. J. McKellar, and Andrew A. Rawlinson

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 835 | Cited 2 times

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We review how antiparticles may be introduced in classical relativistic mechanics, and emphasize that many of their paradoxical properties can be more transparently understood in the classical than in the quantum domain. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
03.30.+p Special relativity
03.65.Pm Relativistic wave equations

A mechanical Duffing oscillator for the undergraduate laboratory

J. E. Berger and G. Nunes, Jr.

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 841 | Cited 5 times

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The design and construction of a mechanical Duffing oscillator suitable for use in an undergraduate laboratory is described. The oscillator provides a straightforward introduction to nonlinear vibrations and chaotic behavior that is both pedagogically appealing and easily adapted to students at various levels of sophistication. Good agreement is observed between the motion of the oscillator and computer simulations, which provides students with an introduction to the power of mathematical modeling. Period-doubling routes to chaos can be observed both experimentally and numerically. © 1997 American Association of Physics Teachers.
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01.50.Pa Laboratory experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems
05.45.-a Nonlinear dynamics and chaos

Equilibrium charge density on a conducting needle

Mark Andrews

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 846 | Cited 5 times

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The concept of an equilibrium continuous charge density on a conducting line, although in some ways unphysical, does provide useful physical insight into needlelike conductors. It is shown that the charge density on such a line must be uniform. A simple method is developed for calculating the charge density on long, thin conductors with circular cross section. Also, the equilibrium distribution of N equal charges on a line is shown to approach equal spacing (except near the ends) as the number of charges grows. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.-q Applied classical electromagnetism

Magnetic braking revisited

J. M. Aguirregabiria, A. Hernández, and M. Rivas

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 851 | Cited 5 times

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The braking force acting on a conducting disk rotating under the influence of an external magnetic field of axial symmetry is calculated in a quasi-static approximation and the role played by the charge distributions induced in the disk is shown. The two cases of infinite and finite radius are considered to analyze the influence of edge effects and we obtain a general expression for the braking torque when the magnetic field has axial symmetry. The particular case of a uniform external magnetic field is used to show the working of a simplified model of a cylindrical battery. Analytical results are compared with those obtained by other authors. © 1997 American Association of Physics Teachers.
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41.20.-q Applied classical electromagnetism
75.80.+q Magnetomechanical effects, magnetostriction

Is it possible to detect permanent electric dipole moments using fluorescence measurements?

Renato Ejnisman and Nicholas P. Bigelow

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 856

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We investigate the interaction of two-level atoms possessing finite permanent electric dipole moments with electromagnetic radiation. After framing the problem in a historical perspective, we solve it in the interaction picture and examine the possibility of extracting information on atomic permanent dipole moments from fluorescence measurements. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
32.50.+d Fluorescence, phosphorescence (including quenching)
32.30.-r Atomic spectra
32.80.-t Photoionization and excitation

Decomposition of electromagnetic fields into radiation and bound components

E. Comay

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 862 | Cited 4 times

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The decomposition of electromagnetic fields for a system of elementary classical point charges into velocity fields and acceleration fields is suggested by the appropriate terms in the Lienard–Wiechert formulas. This paper introduces “bound” fields and “radiation” fields which are related but not identical to velocity and acceleration fields, respectively. It is shown how this approach can be used in the construction of an energy–momentum tensor that is free of infinite quantities and settles the 4/3 problem in the Lorentz transformation of momentum. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.-q Applied classical electromagnetism

Experimenting with magnetism: Ways of learning of Joann and Faraday

Elizabeth Cavicchi

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 867 | Cited 3 times

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This paper narrates learning as it evolved through experimental work and interpretation in two distinct investigations: the explorations of permanent magnets and needles conducted by a student, Joann, as I interactively interviewed her, and Faraday’s initial experimenting with diamagnetism, as documented in his Diary. Both investigators puzzled over details, revisited their confusions resiliently, and invented analogies as ways of extending their questioning; “misconceptions” and conflict were not explicit to their process. Additionally, Faraday formed interpretations—and doubts critiquing them—that drew upon his extensive experience with magnetism’s spatial behaviors. These two cases suggest that physics instruction could include opportunities for students’ development of their own investigatory learning. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

Energy and momentum for the electromagnetic field described by three outstanding electrodynamics

Antonio Accioly

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 882

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A prescription for computing the symmetric energy–momentum tensor from the field equations is presented. The method is then used to obtain the total energy and momentum for the electromagnetic field described by Maxwell electrodynamics, Born–Infeld nonlinear electrodynamics, and Podolsky generalized electrodynamics, respectively. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
03.50.De Classical electromagnetism, Maxwell equations

Electric polarizability of a relativistic particle

M. A. Maize, S. Paulson, and A. D’Avanti

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 888 | Cited 6 times

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A simple potential model is used to study the contribution of negative energy states to the static electric polarizability of a relativistic particle which is bound by a one-dimensional delta potential. The potential includes both Lorentz scalar and vector components. Contrary to the result based on nonrelativistic physics, we find it possible that the electric polarizability can have a negative sign. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
03.30.+p Special relativity
03.65.-w Quantum mechanics

Magnets at the corners of polygons

Daniel R. Stump, Gerald L. Pollack, and Jerzy Borysowicz

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 892 | Cited 1 time

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We consider the statics and dynamics of N identical magnetic dipoles, with inertia, pinned at the corners of a regular polygon with N sides. We show that at equilibrium all dipoles are aligned tangent to the circumscribed circle. We find the normal modes and frequencies for oscillations about equilibrium, and discuss the dispersion relation. In the highest frequency normal mode the dipoles oscillate in phase with equal amplitudes, so no magnetic dipole radiation is emitted. In the limit N→∞, the equilibrium energy and the frequency of the symmetric mode are both related to ζ(3), where ζ is the Riemann zeta function. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.55.Db Generation of magnetic fields; magnets
02.10.-v Logic, set theory, and algebra

A heuristic way of obtaining the Kerr metric

Jörg Enderlein

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 897 | Cited 1 time

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An intuitive, straightforward way of finding the metric of a rotating black hole is presented, based on the algebra of differential forms. The representation obtained for the metric displays a simplicity which is not obvious in the usual Boyer–Lindquist coordinates. © 1997 American Association of Physics Teachers.
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97.60.Lf Black holes
01.50.-i Educational aids
04.70.-s Physics of black holes
95.30.Sf Relativity and gravitation
02.10.-v Logic, set theory, and algebra
04.20.Gz Spacetime topology, causal structure, spinor structure

Making a pitch for the center of mass and the moment of inertia

W. N. Mei and Dan Wilkins

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 903

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We propose some simple experiments to measure moments of inertia of certain physical pendula having high and low symmetry. Periods of oscillation, mass, and distance of the pivot from the center of mass are used to measure ICM for: (a) the “floating eagle,” an intriguing toy, and (b) a rectangular plate. Values of ICM obtained from measurements about different parallel axes may be checked for consistency. © 1997 American Association of Physics Teachers.
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01.50.My Demonstration experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems

Unified mean-field study of ferro- and antiferromagnetic behavior of the Ising model with external field

Eduard Vives, Teresa Castán, and Antoni Planes

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 907 | Cited 3 times

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A simultaneous mean-field treatment, of both phenomena, ferro- and antiferromagnetism, in the framework of the Bragg–Williams theory, shows the importance of the interplay between the two corresponding order parameters in determining the features of the phase diagram. The problems of phase separation and order–disorder transition in binary alloys are also included in the solution. The different projections of the phase diagram are discussed. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
75.10.Hk Classical spin models
05.50.+q Lattice theory and statistics (Ising, Potts, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

The magnetic field of a current carrying cosmic string

A. G. R. Muriano and M. F. A. da Silva

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 914 | Cited 1 time

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The magnetostatic field of an infinite rectilinear current placed in the stationary gravitational field of a rotating cosmic string is found. An interesting aspect of this problem is that although the metric is mathematically very simple, its physical meaning is not trivial. It depends only on topological parameters. So, the cosmic string vacuum space–time is locally equivalent to the Minkowski space–time, but not globally. The calculations are so simple that they can easily be shown in the classroom. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
95.30.Sf Relativity and gravitation
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology

Modern optical signal processing experiments demonstrating intensity and pulse-width modulation using an acousto-optic modulator

Ting-Chung Poon, Mark D. McNeill, and Daniel J. Moore

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 917 | Cited 2 times

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Two experiments are presented to introduce undergraduate students in electrical engineering or physics to modern optical signal processing. Both experiments use an acousto-optic (AO) Bragg cell together with additional electronics to modify the intensity of a laser beam. Specifically, we show how an AO feedback system operating in the Bragg regime can be configured to produce amplitude modulated (AM) and pulse-width modulated optical signals. The basic components of the AO feedback system include a laser, an AO Bragg cell, an electronic AM modulator, a photodetector, an amplifier, and an electronic adder. Except for the laser, the AM modulator, and the Bragg cell, each of these components can be constructed with low cost electronics. A tutorial outlining the principles of acousto-optics is included to provide sufficient understanding of the Bragg cell. The project described in the paper has been used as a demonstration for junior- and senior-level undergraduate students in electrical engineering communications and optics classes. © 1997 American Association of Physics Teachers.
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01.50.Pa Laboratory experiments and apparatus
42.79.Hp Optical processors, correlators, and modulators
42.79.Jq Acousto-optical devices
43.38.Zp Acoustooptic and photoacoustic transducers
43.60.-c Acoustic signal processing
42.30.Lr Modulation and optical transfer functions
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Comment on “Specific heats and the equipartition law in introductory textbooks,” by Clayton A. Gearhart [Am. J. Phys. 64 (8), 995–1000 (1996)]

L. Kannenberg

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 926

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01.50.-i Educational aids
05.70.-a Thermodynamics
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Comment on “Vacuum catastrophe: An elementary exposition of the cosmological constant problem,” by Ronald J. Adler, Brendan Casey, and Ovid C. Jacob [Am. J. Phys. 63 (7), 620–626 (1995)]

Stanford R. Ovshinsky and Hellmut Fritzsche

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 927

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Abstract Unavailable
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01.50.-i Educational aids
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology
03.70.+k Theory of quantized fields
95.30.Sf Relativity and gravitation
04.20.-q Classical general relativity

Response to S. R. Ovshinsky and H. Fritzsche’s “Comment on ‘Vacuum catastrophe: An elementary exposition of the cosmological constant problem’ ” [Am. J. Phys. 65 (9), 927 (1997)]

Ronald J. Adler and Ovid C. Jacob

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 928

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01.50.-i Educational aids
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology
04.20.Cv Fundamental problems and general formalism

Comment on “Maxwell’s equations in a rotating medium: Is there a problem?,” by G. N. Pellegrini and A. R. Swift [Am. J. Phys. 63 (8), 694–705 (1995)]

Michael L. Burrows

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 929 | Cited 5 times

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01.50.-i Educational aids
03.50.De Classical electromagnetism, Maxwell equations
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Laser Fundamentals

William T. Silfvast, Author and Paul J. H. Tjossem, Reviewer

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 932

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Abstract Unavailable
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01.30.-y Physics literature and publications
01.50.-i Educational aids
42.55.-f Lasers
42.60.-v Laser optical systems: design and operation

Particle Physics: One Hundred Years of Discoveries

V. V. Ezhela, Author and Davison E. Soper, Reviewer

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 932

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Abstract Unavailable
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01.50.-i Educational aids
01.30.mm Textbooks for graduates and researchers

Models and Modelers of Hydrogen

Akhlesh Lakhtakia, Editor and Edwin E. Salpeter, Reviewer

American Journal of Physics -- September 1997 -- Volume 65, Issue 9, pp. 933

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Abstract Unavailable
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01.30.Rr Surveys and tutorial papers; resource letters
03.65.-w Quantum mechanics
24.75.+i General properties of fission
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