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Dec 1995

Volume 63, Issue 12, pp. 1065-1157

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Question ♯30. How are positrons moderated?

Thomas D. Rossing

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1065

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14.60.Cd Electrons (including positrons)
29.27.Eg Beam handling; beam transport
41.85.-p Beam optics

Question ♯31. Does any piece of mathematics exist for which there is no application whatsoever in physics?

Dwight E. Neuenschwander

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1065

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01.55.+b General physics
01.70.+w Philosophy of science

Question ♯32. How do gravitons interact with black holes?

David L. Wallach

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1065

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04.60.-m Quantum gravity
04.70.-s Physics of black holes

Answer to Question ♯10 [‘‘Cooling and expansion of the universe,’’ J. Richard Christman, Am. J. Phys. 63 (1), 13 (1995)]

Lior M. Burko

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1065

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05.70.Ce Thermodynamic functions and equations of state
98.80.Bp Origin and formation of the Universe
98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)

Answers to Question ♯10 [‘‘Cooling and expansion of the universe,’’ J. Richard Christman, Am. J. Phys. 63 (1), 13 (1995)] and Question ♯17 [‘‘What happens to energy in the cosmic expansion?’’ Frank Munley, Am. J. Phys. 63 (5), 394 (1995)]

Steve Blau

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1066

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04.20.Cv Fundamental problems and general formalism
05.70.Ce Thermodynamic functions and equations of state
98.80.Bp Origin and formation of the Universe
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology

Answer to Question ♯10 [‘‘Cooling and expansion of the universe,’’ J. Richard Christman, Am. J. Phys. 63(1), 13 (1995)]

David Keeports

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1067

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05.70.Ce Thermodynamic functions and equations of state
98.80.Bp Origin and formation of the Universe
98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)

Answer to Question ♯17 [‘‘What happens to energy in the cosmic expansion?’’ Frank Munley, Am. J. Phys. 63(5), 394 (1995)]

W. N. Mathews, Jr.

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1067

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03.30.+p Special relativity
98.80.Bp Origin and formation of the Universe
98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology

Answer to Question ♯17 [‘‘What happens to energy in the cosmic expansion?’’ Frank Munley, Am. J. Phys. 63 (5), 394 (1995)]

R. H. Garstang

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1067

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98.80.Bp Origin and formation of the Universe
98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology
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Guest Comment: What do graduate oral exams tell us?

David Hestenes

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1069

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01.40.G- Curricula and evaluation
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The new morning of the world

Richard Rhodes

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1070

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A lecture delivered at the annual conference of the American Association of Physics Teachers, Spokane, Washington, 9 August 1995.
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01.10.Fv Conferences, lectures, and institutes
01.65.+g History of science
01.75.+m Science and society

Potential distribution in the van der Pauw technique

D. K. de Vries and A. D. Wieck

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1074 | Cited 2 times

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The van der Pauw technique for resistivity and Hall measurements is illustrated on large‐scale models of conductive polyethylene, which can be used to visualize the potential distribution in arbitrarily shaped two‐dimensional samples. The equipotential lines in a square sample and the dependence of measured voltages on the aspect ratio of these samples are studied. We give examples of the use of conformal mapping in two‐dimensional conduction. © 1995 American Association of Physics Teachers.  
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01.50.Pa Laboratory experiments and apparatus
07.68.+m Photography, photographic instruments; xerography

Modernizing introductory physics

C. H. Holbrow, J. C. Amato, E. J. Galvez, and J. N. Lloyd

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1078 | Cited 4 times

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Since 1985 the Colgate University Department of Physics and Astronomy has been reshaping the first term of introductory calculus‐level physics to answer the question: ‘‘Why do we believe in atoms and the properties ascribed to them?’’ This paper describes the new course, its 400‐page text, its ten laboratories, its six computer exercises, and how these work together successfully to serve several purposes: For those students who do not continue on with any more physics, it is a good introduction to physics; for the many students whose quantitative skills need enhancing, it provides a better chance to improve those skills than traditional introductory physics; by its emphasis on wave‐particle duality and mass‐energy equivalence, the course introduces students to important quantum and relativistic ideas that are fundamental to most of what contemporary physicists actually do. We also extract from our reform efforts some lessons useful to anyone undertaking to change introductory physics. © 1995 American Association of Physics Teachers.
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01.40.G- Curricula and evaluation

Teaching physics on line

Richard C. Smith and Edwin F. Taylor

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1090 | Cited 8 times

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Since 1986 we have offered courses on special relativity and general relativity in a variety of formats over computer networks nationwide to a mix of high school students, high school teachers, college students, and college professors. Using ideas from many sources, we have evolved a highly structured format that keep students working every day and talking extensively with one another over the conference system. Obligatory student ‘‘Reading Memos’’ bring a flood of comments and complaints essential to evaluation of student progress and revision of the text. We consider possible reasons why these courses from the United States have not worked with participants in Europe, and speculate about possible consequences of future technological developments. © 1995 American Association of Physics Teachers.
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01.50.ht Instructional computer use
03.30.+p Special relativity

Electronic paramagnetism in biomolecular structure and function

A. S. Brill, F. G. Fiamingo, and B. S. Gerstman

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1096

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Intrinsic paramagnetic states are ubiquitous in biological systems, and extrinsic paramagnetic probes are often introduced in studies of biomolecular structure. The measurements of electron paramagnetic resonance and magnetic susceptibility are commonly employed in investigations of biomolecular paramagnetism. How the data obtained from these measurements are used to arrive at electronic structure, and how the electronic structure and its changes relate to biologically functional processes, are the subjects of this review. Emphasis is placed upon the role of magnetic measurements in quantifying the special properties which proteins confer upon iron and copper ions. © 1995 American Association of Physics Teachers.  
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36.20.-r Macromolecules and polymer molecules
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
87.15.B- Structure of biomolecules

A simple mechanical model for the diatomic molecule exhibiting a magnetic monopole in nuclear dynamics

Jason Foat and Kai S. Lam

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1114

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A very simple model of a diatomic molecule—a rigid dumbbell‐flywheel system—is used to illustrate the close relationship between molecular dynamics and gauge fields. It is shown that, under the adiabatic approximation and certain assumptions, even a simple classical analysis yields a Lorentz force in nuclear dynamics due to a magnetic monopole gauge field. This classical treatment, however, fails to explain the origin of the ‘‘magnetic’’ force. An exact quantum mechanical treatment based on relinquishing the Born–Oppenheimer approximation reveals unambiguously both the origin and the nature of the monopole gauge potential, justifies the adiabatic approximation, and yields an expression for the energy eigenvalues. We believe this simple and exactly solvable model is not only suitable as a pedagogical tool for molecular dynamics, but also ideal for communicating some aspects of the physics behind gauge field theories to advanced undergraduates. © 1995 American Association of Physics Teachers.
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33.20.-t Molecular spectra
34.20.Cf Interatomic potentials and forces

The Foldy–Wouthuysen transformation

John P. Costella and Bruce H. J. McKellar

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1119 | Cited 17 times

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The Foldy–Wouthuysen transformation of the Dirac Hamiltonian is generally taught as simply a mathematical trick that allows one to obtain a two‐component theory in the low‐energy limit. It is not often emphasized that the transformed representation is the only one in which one can take a meaningful classical limit, in terms of particles and antiparticles. We briefly review the history and physics of this transformation. © 1995 American Association of Physics Teachers.
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03.65.Pm Relativistic wave equations

A new statement of the second law of thermodynamics

Alan Macdonald

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1122

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A new statement of the second law of thermodynamics is given. The law leads almost effortlessly, for very general closed systems, to a definition of absolute entropy S, a demonstration that ΔS≥0 in adiabatic processes, a definition of temperature, and a demonstration that dS≥δQ/T in quasistatic processes. Entropy is given a clear physical meaning. © 1995 American Association of Physics Teachers.  
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05.70.Ce Thermodynamic functions and equations of state

Chaotic pendulum based on torsion and gravity in opposition

Randall D. Peters

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1128 | Cited 4 times

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An unconventional driven torsion pendulum influenced by gravity has been studied for chaos. Through the use of a symmetric differential capacitive sensor and a galvanometer, phase‐space trajectories were generated with an x–y recorder. These were then later compared against output from a computer model of the system which has been further used to generate Poincaré sections, Fourier transforms, and time records. Sensitive dependence on initial conditions as a function of frequency and drive amplitude was demonstrated. © 1995 American Association of Physics Teachers.
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05.45.-a Nonlinear dynamics and chaos
45.05.+x General theory of classical mechanics of discrete systems

Off‐axis illumination and its relation to partial coherence

Matt Young and Paul D. Hale

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1136 | Cited 1 time

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We calculate the partially coherent images of an edge in one dimension by the method of adding intensities, that is, by modeling the illumination as an array of mutually incoherent plane waves incident over a range of angles. In order to visualize the transition between coherent and incoherent imaging, we display images that result from such off‐axis plane waves; these images change considerably as the angle of illumination changes. The calculations are easily carried out on a microcomputer with a high‐level mathematics program. The results shed light on off‐axis and dark‐field illumination as well. Finally, we elucidate a distinction between imaging with the aperture stop in the transform plane and imaging with the aperture stop distant from the transform plane.
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42.25.Kb Coherence

Excited‐state solutions for an infinite family of one‐dimensional potentials

B. Cameron Reed

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1141 | Cited 1 time

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A method of generating analytically and numerically exact ground and excited‐state wave functions and energies of an infinite family of one‐dimensional potentials is described. Explicit application to a sixth‐order polynomial potential is presented. © 1995 American Institute of Physics.  
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03.65.Ge Solutions of wave equations: bound states
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Erratum: Entropy and heat along reversible paths for fluids and magnets [Am. J. Phys. 63, 814–817 (1995)]

Harvey S. Leff

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1146

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Abstract Unavailable
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05.70.Ce Thermodynamic functions and equations of state
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
99.10.Cd Errata

Parametric analysis of mean‐field ferromagnetic and antiferromagnetic susceptibilities

Y. T. Millev and M. A. B. Whitaker

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1146

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75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Lorentz transformations directly from the speed of light

Bernhard Rothenstein and George Eckstein

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1150 | Cited 2 times

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Abstract Unavailable
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03.30.+p Special relativity

Smooth transitions between the three damping cases for the harmonic oscillator

Francis J. McCormack

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1151

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01.50.Kw Techniques of testing
45.05.+x General theory of classical mechanics of discrete systems
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Using a PC as a frequency meter or a counter

J. Sartori, T. Catunda, and L. A. O. Nunes

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1152

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Abstract Unavailable
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01.50.Pa Laboratory experiments and apparatus
06.30.Ft Time and frequency
07.05.-t Computers in experimental physics
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Post‐Use Review. Principles of Physics

Raymond A. Serway, Author, Alfonso M. Albano, James Arrison, and Tina M. Mello

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1154

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Abstract Unavailable
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01.30.mp Textbooks for undergraduates
01.55.+b General physics

Quantum Mechanics: Historical Contingency and the Copenhagen Hegemony

James T. Cushing, Author and Tim Maudlin

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1155

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Abstract Unavailable
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01.30.Ee Monographs and collections
03.65.Ta Foundations of quantum mechanics; measurement theory

The Collected Works of Eugene Paul Wigner. Part A: Scientific Papers. Volume V: Nuclear Energy

Alvin M. Weinberg, Author, Alfred M. Perry, Author, and Lawrence Ruby

American Journal of Physics -- December 1995 -- Volume 63, Issue 12, pp. 1156

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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
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