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Dec 1997

Volume 65, Issue 12, pp. 1133-1220

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Question #67. The electric field outside a black hole

Mano Singham

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1133 | Cited 2 times

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Abstract Unavailable
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01.50.-i Educational aids
04.70.-s Physics of black holes
97.60.Lf Black holes
04.60.-m Quantum gravity

Question #68. 60.000 Hz? Synchronization of the power grid

Robert H. Romer

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1133

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01.50.-i Educational aids
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Answer to Question #4. Is there a physics application that is best analyzed in terms of continued fractions?

Barry R. Holstein

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1133 | Cited 2 times

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01.50.-i Educational aids
02.10.-v Logic, set theory, and algebra
03.65.Ge Solutions of wave equations: bound states

Answer to Question #24. Can an electron be at rest?

Nick Huggett

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1135

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01.50.-i Educational aids
03.65.Ge Solutions of wave equations: bound states
03.65.Sq Semiclassical theories and applications

Answer to Question #56. Ice cream making

F. Herrmann

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1135 | Cited 1 time

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01.50.-i Educational aids
64.70.D- Solid-liquid transitions
65.20.-w Thermal properties of liquids
65.40.gd Entropy
82.60.Hc Chemical equilibria and equilibrium constants

Answer to Question #56. Ice cream making

Jonathan Mitschele

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1136 | Cited 1 time

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01.50.-i Educational aids
05.70.Jk Critical point phenomena
64.70.-p Specific phase transitions
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Guest Comment: Science standards and state testing

Alan Cromer

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1138

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01.40.E- Science in school
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David J. Griffiths: Recipient of the Robert A. Millikan Medal

Robert C. Hilborn

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1140

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01.10.Cr Announcements, news, and awards

Millikan Lecture 1997: Is there a text in this class?

David J. Griffiths

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1141

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I’ll propose a physicist’s answer to Stanley Fish’s impudent question, and offer some thoughts about the role of text(book)s in the teaching and learning process. Also—with a view to offending as many listeners as possible—I will indulge in some gratuitous curmudgeonly remarks about the reform movement in physics education. © 1997 American Association of Physics Teachers.
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01.10.Fv Conferences, lectures, and institutes
01.50.-i Educational aids
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An analytically solvable model of dissipation

U. Fano

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1144 | Cited 1 time

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The initial energy of a pendulum weakly coupled to a stretched string of infinite length dissipates into waves traveling away along the string. The frequency spectrum of this process emerges from a simple algebraic procedure resting on its key features. Confining the string to a long but finite length revives the pendular motion periodically. This model illustrates basic aspects of dissipation, providing material for exercises on physicomathematical techniques. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
45.05.+x General theory of classical mechanics of discrete systems
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Dynamic modeling of speed skiing

R. S. Catalfamo

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1150 | Cited 1 time

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The equations of motion that describe a skier descending a speed-skiing hill are solved both analytically and numerically. The model is shown to agree well with actual official results but only when the hill profile is considered. A sensitivity analysis reveals which parameters most affect the skier’s exit speed. Other factors, such as scaling effects and wind gusts, are included to determine whether these need to be considered in official results. One surprising result is that, under certain conditions and hill profiles, maximum skier speed is attained prior to entry into the timing zone—thus bringing into question the optimum placement of the timing gates. © 1997 American Association of Physics Teachers.
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01.55.+b General physics
01.50.-i Educational aids
45.05.+x General theory of classical mechanics of discrete systems

Why is the propagation velocity of a photon in a transparent medium reduced?

Bart G. de Grooth

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1156 | Cited 2 times

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A path integral formalism is used to describe the propagation of photons through a transparent medium. It is shown that the reduced phase velocity of light can be understood quantitatively by taking into account the contribution of all the possible classical paths the photon could have taken in order to reach a detector. These paths include all the multiple scattering processes by the atoms in the medium. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
42.25.Gy Edge and boundary effects; reflection and refraction
42.25.Bs Wave propagation, transmission and absorption
42.50.Ct Quantum description of interaction of light and matter; related experiments

Some properties of cycloid trajectories

Ian Bruce

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1164 | Cited 1 time

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The electric and magnetic forces acting on an ion in uniform crossed fields are shown to add to give a centripetal force of constant magnitude, moving with the ion in a cycloid trajectory. A comparison is made with the analogous forces in the classical brachistrochrone case of a bead sliding down a frictionless cycloid-shaped wire. © 1997 American Association of Physics Teachers.
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41.00.00 Electromagnetism; electron and ion optics
01.50.-i Educational aids

Visualizing classical periodic orbits from the quantum energy spectrum via the Fourier transform: Simple infinite well examples

Richard W. Robinett

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1167 | Cited 11 times

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The Fourier transform of the density of quantized energy levels for a quantum mechanical particle in a two-dimensional (2-D) infinite well (or billiard geometry) is known to exhibit δ-function-like spikes at distance values (L) corresponding to the lengths of periodic orbits or closed trajectories. We show how these Fourier transforms can be rather easily calculated numerically for simple infinite well geometries including the square and rectangular well in 2 D, the cubical well in three dimensions, as well as the circular infinite well (and variations) in two dimensions. Such calculations provide a novel, well-motivated, and relatively straightforward example of numerical Fourier transform techniques and make interesting connections between quantum energy levels and classical trajectories in a way which is seldom stressed in the undergraduate curriculum. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
03.65.Sq Semiclassical theories and applications
03.65.Ge Solutions of wave equations: bound states
02.30.Nw Fourier analysis
02.30.Uu Integral transforms
02.30.Vv Operational calculus

The fields outside a long solenoid with a time-dependent current

Kirk T. McDonald

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1176

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An instructive version of this well-known problem is the case of a current that is zero to t<0 and varies as αt for t>0. A generally excellent discussion of this case by Abbott and Griffiths features, however, a singularity in the fields at any point at the moment they first become nonzero. This singularity can be avoided by careful approximation, derived here using expressions for time-dependent fields rather than potentials. The result is that while the fields assume a quasistatic character for long times after the current has started to flow, they include a small amount of radiation at short times. Such an effect was observed in a simple experiment involving a kitchen appliance. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.-q Applied classical electromagnetism

Friction forces on charges moving outside of a conductor due to Ohm’s law heating inside of a conductor

M. S. Tomassone and A. Widom

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1181 | Cited 4 times

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It is very well known and taught to undergraduate students of electromagnetic theory that a charge e sitting at a height h above a conductor feels a force Fstatic=−(e2/4h2)N, where N is a unit normal vector to the conductor surface. The static force is due to an induced conductor charge density. Suppose (i) that the charged particle has a small velocity V parallel to the conductor surface, and (ii) that the induced conductor currents obey Ohm’s law with conductivity σ. Ohm’s law induced heating in the conductor then gives rise to a friction force (over and above the static force) Ffriction=−(e2/16πσh3)V. A simple derivation of this friction provides the undergraduate student with an interesting physical example of an induced friction force acting at a distance, i.e., a charged particle moving in the vacuum can feel a friction force due to a neighboring conductor. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.-q Applied classical electromagnetism
46.55.+d Tribology and mechanical contacts

Comment on “A simple, conservative understanding of many time-driven systems,” by Harvey Kaplan [Am. J. Phys. 62 (12), 1097–1099 (1994)]

C. M. Giordano, A. R. Plastino, and A. Plastino

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1183

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We show that Kaplan’s approach to time-driven systems provides interesting insights in regards to the problem of the motion of a particle in a uniformly rotating potential. Further, it allows for establishing a connection with the problem of a particle in a potential with cylindric helicoidal symmetry. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
45.05.+x General theory of classical mechanics of discrete systems

Quantum Hamilton–Jacobi formalism and the bound state spectra

R. S. Bhalla, A. K. Kapoor, and P. K. Panigrahi

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1187 | Cited 10 times

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It is well known in classical mechanics that the frequencies of a periodic system can be obtained rather easily through the action variable, without completely solving the equation of motion. Analogously, the equivalent quantum action variable appearing in the quantum Hamilton–Jacobi formalism can provide the energy eigenvalues of a bound state problem, without the necessity of solving the corresponding Schrödinger equation explicitly. This elegant and useful method is elucidated here in the context of some known and not so well-known solvable potentials. It is also shown how this method provides an understanding as to why approximate quantization schemes such as ordinary and supersymmetric WKB can give exact answers for certain potentials. © 1997 American Association of Physics Teachers.
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03.65.Sq Semiclassical theories and applications
03.65.Ge Solutions of wave equations: bound states

A simple calculation of the deflection of light in a Schwarzschild gravitational field

L. Lerner

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1194 | Cited 1 time

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The problem of the deflection of light in a medium with varying refractive index is applied to the motion of light in a weak Schwarzschild gravitational field. In contrast to the standard deviation, the present method is physically transparent, providing a clear reason for the factor-of-2 deviation of the general relativistic result from that of the Newtonian theory without any detailed calculation. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
04.20.Cv Fundamental problems and general formalism

Bell and Greenberger, Horne, and Zeilinger theorems revisited

Luiz Carlos Ryff

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1197 | Cited 6 times

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The original theorems of Bell and of Greenberger, Horne, and Zeilinger (GHZ) are extended from ideal to real situations using an intuitive and straightforward approach. This alternative derivation has the merit of showing that if a theorem is valid whenever we have perfect correlations, it cannot be totally wrong in the case of almost perfect correlations. Therefore, it is probably easy (i.e., by introducing only small changes in the original argument) to extend the result to deal with imperfect correlations. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
03.65.Ta Foundations of quantum mechanics; measurement theory

A curvature-based derivation of the Schwarzschild metric

Mariano Santander, Luis M. Nieto, and Nicolás A. Cordero

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1200

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We give a derivation of Schwarzschild and other spherically symmetric solutions in general relativity which starts by computing the curvatures directly from Einstein’s equations and Bianchi identities, and then derives the metric. This transforms the “plausibility” argument for the Schwarzschild metric given by Berry in his book Principles of Cosmology and Gravitation into a complete derivation, which puts the stress from the beginning on the curvatures, the quantities which actually correspond to the gravitational field. © 1997 American Association of Physics Teachers.
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01.50.-i Educational aids
04.20.-q Classical general relativity
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Comment on “Lorentz transformations directly from the speed of light,” by B. Rothenstein and G. Eckstein [Am. J. Phys. 63 (12), 1150 (1995)]

Edward Kapuścik

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1210 | Cited 1 time

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Abstract Unavailable
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03.30.+p Special relativity
01.40.-d Education

A novel approach to Faraday’s law

Jack Higbie

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1211

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

Comment on “Continued fractions and the harmonic oscillator using Feynman’s path integrals,” by L. Q. English and R. R. Winters [Am. J. Phys. 65 (5), 390–393 (1997)]

K. Unnikrishnan

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1212 | Cited 1 time

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01.50.-i Educational aids
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Neutron optical activity and the weak force

C. R. Gould

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1213

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12.00.00 Specific theories and interaction models; particle systematics
14.20.Dh Protons and neutrons
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Quantum Mechanics: Fundamentals and Applications to Technology

Jasprit Singh, Author and R. D. Murphy, Reviewer

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1218

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Abstract Unavailable
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01.30.-y Physics literature and publications
03.65.-w Quantum mechanics

Quantum Mechanics: Classical Results, Modern Systems and Visualized Examples

Richard W. Robinett, Author and R. D. Murphy, Reviewer

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1218

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Abstract Unavailable
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01.30.-y Physics literature and publications
03.65.-w Quantum mechanics

Giant Molecules: Here, There, and Everywhere…

Alexander Yu. Grosberg, Author, Alexei R. Khokhlov, Author, and Lynn W. Jelinski, Reviewer

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1218

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36.20.-r Macromolecules and polymer molecules
61.41.+e Polymers, elastomers, and plastics
83.80.-k Material type
87.15.-v Biomolecules: structure and physical properties
64.60.A- Specific approaches applied to studies of phase transitions
47.53.+n Fractals in fluid dynamics

The Dawning of Gauge Theory

Lochlainn O’Raifeartaigh, Author and Robert Mills, Reviewer

American Journal of Physics -- December 1997 -- Volume 65, Issue 12, pp. 1219

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Abstract Unavailable
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01.65.+g History of science
01.50.-i Educational aids
11.15.-q Gauge field theories
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