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Dec 1993

Volume 61, Issue 12, pp. 1065-1158

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Editorial: Magnetic monopoles or cross products? Is physics too difficult?

Robert H. Romer

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1065

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Abstract Unavailable
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14.80.Hv Magnetic monopoles
01.40.Di Course design and evaluation
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Klopsteg Memorial Lecture (August, 1992): What science knows about violins—and what it does not know

Gabriel Weinreich

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1067 | Cited 4 times

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This is the edited text of the Klopsteg Lecture delivered to the Summer Meeting of the AAPT on August 13, 1992. It sketches the current state of knowledge about the violin—at least as seen by the author—in two parts, Physics of the Bowed String and The Violin as a Radiator of Sound, punctuated by a number of ‘‘meditations’’ about the nature of scientific knowledge.  
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43.75.De Bowed stringed instruments

Fluctuation and dissipation in Brownian motion

Daniel T. Gillespie

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1077 | Cited 6 times

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An analysis of Brownian motion based upon a ‘‘Langevin equation’’ form of Newton’s second law provides a physically motivated introduction to the theory of continuous Markov processes, which in turn illuminates the subtle mathematical underpinnings of the Langevin equation. But the Langevin approach to Brownian motion requires one to assume that the collisional forces of the bath molecules on the Brownian particle artfully resolve themselves into a ‘‘dissipative drag’’ component and a ‘‘zero‐mean fluctuating’’ component. A physically more plausible approach is provided by a simple discrete‐state jump Markov process that models in a highly idealized way the immediate effects of individual molecular collisions on the velocity of the Brownian particle. The predictions of this jump Markov process model in the continuum limit are found to precisely duplicate the predictions of the Langevin equation, thereby validating the critical two‐force assumption of the Langevin approach.
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05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

The electrostatics and magnetostatics of a conducting disk

R. Friedberg

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1084 | Cited 3 times

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A method due to Copson for treating the electrostatics of a disk is modified so that each step can be understood physically. Using this method we easily find the capacitance 2a/π and the electric polarizability 4a3/3π of a conducting disk. We also find in closed form the Green’s function along the axis and the self‐force (the force due to induced charges) on a point charge on the axis. We similarly treat magnetic problems, finding the normal polarizability of a superconducting disk and the ‘‘levitating’’ force on a point monopole or vertical point dipole on the axis. All results are in closed form.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

A quantitative magnetic braking experiment

Cyrus S. MacLatchy, Philip Backman, and Larry Bogan

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1096 | Cited 11 times

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A popular demonstration which often accompanies the introduction of magnetic induction is that in which a strong button‐shaped magnet is dropped through a long copper or aluminum tube. The induced currents cause a retarding force which dramatically slows the descent of the falling magnet. Here, we describe methods of calculating and measuring the terminal velocity and magnetic forces in the magnetic braking experiment. The techniques are quite accurate, inexpensive to perform, and are suitable for introductory courses in electricity and magnetism.
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01.50.My Demonstration experiments and apparatus
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Effective mass of a classical linear chain

E. N. Martínez

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1102 | Cited 3 times

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After a short introduction to response functions, the force‐acceleration response function is calculated for a forced classical semi‐infinite linear chain. This response function, which can be called a frequency‐dependent inverse effective mass, allows a thorough and graphical discussion of motions and energy transport in the chain. The nature of extended motions for forcing frequencies within the band and of localized surface modes for high frequencies is clearly shown by this treatment.
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45.05.+x General theory of classical mechanics of discrete systems
05.50.+q Lattice theory and statistics (Ising, Potts, etc.)

The random walk as an eigenvalue problem

D. R. Franceschetti, E. C. Hunke, X. Zhang, and J. R. Haddock

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1111

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The random walk in one dimension can be effectively used to introduce or reinforce a number of advanced mathematical and physical concepts. Here the behavior of an ensemble of particles executing random walks is discussed as an eigenvalue problem, and as a system for which entropy can be calculated in a nonequilibrium state.
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05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.20.Gg Classical ensemble theory
01.50.Kw Techniques of testing

Photoemission energy distribution measurements in a simple metal: A modern physics undergraduate laboratory

Rosalia Zangara and Elisa Lanzara

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1114 | Cited 1 time

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Measurement of energy distribution curves (EDCs) is one of the more powerful techniques for investigating the electronic band structure of solids. It would be profitable for undergraduate students to perform an experiment introducing them to this aspect of modern spectroscopy. In this paper we describe an arrangement we use in our course of modern physics for engineering students utilizing a commercial photocell. After a theoretical background on the photoemission process in metal, we present measurements on the EDCs obtained by graphical differentiation of the I–V characteristics of the photocell and by using an ac method where the differentiation is performed electronically.
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01.50.Pa Laboratory experiments and apparatus
79.60.Bm Clean metal, semiconductor, and insulator surfaces
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Scattering by a finite periodic potential

D. W. L. Sprung, Hua Wu, and J. Martorell

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1118 | Cited 33 times

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The problem of scattering in one dimension by a potential which consists of N identical cells is solved in a transparent manner. The N‐cell transmission and reflection amplitudes are expressed in terms of the single‐cell amplitudes and the Bloch phase. As examples the results are applied to a row of delta‐function potentials, and to a row of square wells, and it is shown that these expressions provide an immediate understanding of the results of detailed calculations.
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03.65.Db Functional analytical methods
03.65.Nk Scattering theory
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

CAPA—An integrated computer‐assisted personalized assignment system

E. Kashy, B. M. Sherrill, Y. Tsai, D. Thaler, D. Weinshank, M. Engelmann, and D. J. Morrissey

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1124 | Cited 2 times

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A new integrated computer‐assisted personalized assignment (CAPA) system that creates individual assignments for each student has been developed and found to be a powerful motivator. The CAPA system allows students to enter their answers to personalized assignments directly via networked terminals, gives immediate feedback and hints (allowing challenging questions), while providing the instructor with on‐line performance information. The students are encouraged to study together which is known to be an effective learning strategy, but each must still obtain his/her own correct answers. Students are allowed to re‐enter solutions to the problems before the due date without penalty, thus providing students with different skills levels the opportunity and incentive to understand the material without being judged during the learning process. The features and operation of the system are described, observations on its use in an introductory general physics class are reported, and some of the highly favorable student reactions are included.
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01.50.ht Instructional computer use

Classical mechanics and gauge theories

Fabrice Debbasch

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1131 | Cited 1 time

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It is shown that the free motion of a point mass in classical mechanics can be considered as a gauge theory. In such an approach, the gauge fields are the angular and translation velocity of the (possibly noninertial) frame in which the motion is studied. A brief comparison with other gauge theories is made.
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45.05.+x General theory of classical mechanics of discrete systems
11.15.-q Gauge field theories

Simulation of magnetic resonance experiments

Jean‐Philippe Grivet

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1133

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Several experiments in nuclear magnetic resonance have been simulated by numerical integration of the Bloch equations. The behavior of the magnetization vector has been studied in such cases as free precession, pulse excitation, Torrey oscillations, slow, adiabatic, and fast passages through resonance, excitation by Gaussian pulses. The numerical approach proved very convenient to demonstrate the role of the parameters that describe a spin system (T1 and T2) and the influence of the various operating parameters (sweep width and sweep rate, pulse length, frequency offset). Several types of graphic output are shown.
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76.60.-k Nuclear magnetic resonance and relaxation
33.25.+k Nuclear resonance and relaxation

Wormhole connecting two Reissner–Nordstrom universes

Edward G. Harris

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1140 | Cited 2 times

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We find an approximate solution to the Einstein–Maxwell equations that describes two Reissner–Nordstrom universes that are connected by a wormhole. A scalar field with negative energy is necessary to maintain the wormhole.
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04.20.Jb Exact solutions
04.40.-b Self-gravitating systems; continuous media and classical fields in curved spacetime

Proof that the Neumann Green’s function in electrostatics can be symmetrized

K.‐J. Kim and J. D. Jackson

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1144 | Cited 1 time

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We prove by construction that the Green’s function satisfying the Neumann boundary conditions in electrostatic problems can be symmetrized. An illustrative example is given.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
02.30.Em Potential theory
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The Dirac comb and the Kronig‐Penney model: Comment on ‘‘Scattering from a locally periodic potential,’’ by D. J. Griffiths and N. F. Taussig [Am. J. Phys. 60, 883–888 (1992)]

S. J. Blundell

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1147 | Cited 7 times

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03.65.Nk Scattering theory
11.80.-m Relativistic scattering theory

Comment on ‘‘Some remarks on classical electromagnetism and the principle of relativity,’’ by Umberto Bartocci and Marco Mamone Capria [Am. J. Phys. 59, 1030–1032 (1991)]

Dragan V. Redžić

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1149 | Cited 3 times

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Abstract Unavailable
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03.50.De Classical electromagnetism, Maxwell equations
03.30.+p Special relativity

An alternative derivation of diffraction integrals

Augusto Garcia‐Valenzuela

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1150

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Abstract Unavailable
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01.50.Kw Techniques of testing
03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation
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Demonstration of conoscopic pictures

Benjamin S. Perkalskis

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1152 | Cited 1 time

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Abstract Unavailable
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01.50.Pa Laboratory experiments and apparatus
42.25.Lc Birefringence
78.20.Fm Birefringence

Force between the plates of a parallel‐plate capacitor

F. N. Yan and H. K. Wong

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1153 | Cited 2 times

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Abstract Unavailable
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84.32.Tt Capacitors
07.50.-e Electrical and electronic instruments and components

Adapting a small rocket engine to an air track

Fritz Fischbach

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1154

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Abstract Unavailable
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01.50.My Demonstration experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems
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Nobel Prize Women in Science: Their Lives, Struggles, and Momentous Discoveries

Sharon Bertsch McGrayne, Author and Eugenie Vorburger Mielczarek

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1155

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.60.+q Biographies, tributes, personal notes, and obituaries
01.65.+g History of science

Medical Physics: Physics of the Body

John R. Cameron, Author, James G. Skofronick, Author, Roderick M. Grant, Author, and Edward Siegel

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1156

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Abstract Unavailable
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01.30.mp Textbooks for undergraduates
87.10.-e General theory and mathematical aspects

Ernst Mach—A Deeper Look: Documents and New Perspectives.

John Blackmore, Author and Herman Erlichson

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1157

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.60.+q Biographies, tributes, personal notes, and obituaries
01.70.+w Philosophy of science
01.65.+g History of science

Measurements of Newtonian Gravitation: Selected Reprints

G. T. Gillies, Author and James E. Faller

American Journal of Physics -- December 1993 -- Volume 61, Issue 12, pp. 1158

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.30.Rr Surveys and tutorial papers; resource letters
04.90.+e Other topics in general relativity and gravitation (restricted to new topics in section 04)
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