American Journal of Physics 1995 April

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 297-297
Question (number-sign-sharp)15. What space scales participate in cosmic expansion?
Frank Munley

Department of Physics Roanoke College Salem, Virginia 24153

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 297-297
Question (number-sign-sharp)16. Eastward deflection of a falling body
A. P. French

Department of Physics M.I.T. Room 6-101 77 Massachusetts Avenue Cambridge, Massachusetts 02139

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 297-297
Answer to Question (number-sign-sharp)3 [``Why is momentum called p?,'' N. David Mermin, Am. J. Phys. 62 (10), 871 (1994)]
Daniel T. Gillespie

Research and Technology Division Naval Air Warfare Center China Lake, California 93555

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 297-298
Answer to Question (number-sign-sharp)7 [``The spin-statistics theorem,'' Dwight E. Neuenschwander, Am. J. Phys. 62 (11), 972 (1994)]
Henri Bacry

Physique Theorique Universite d'Aix-Marseille Case 907 F 13288 Marseille, cedex 09

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 298-299
Answer to Question (number-sign-sharp)7 [``The spin-statistics theorem,'' Dwight E. Neuenschwander, Am. J. Phys. 62 (11), 972 (1994)]
Robert C. Hilborn

Department of Physics Amherst College Amherst, Massachusetts 01002

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 300-301
Guest Comment: To support basic research and to develop scientific talent
Neal F. Lane

Director, National Science Foundation

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 302-302
Editorial: A century of Resource Letters
Robert H. Romer

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 303-306
One Hundred Resource Letters, 1962(en-dash)1995
A. P. French

Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Roger H. Stuewer
School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 306-317
Resource Letter: TFM-1: Time and frequency measurement
Christine Hackman
Donald B. Sullivan

Time and Frequency Division, National Institute of Standards and Technology, Boulder, Colorado 80303
(Received 26 August 1994; accepted for publication 5 December 1994)
This Resource Letter is a guide to the literature on time and frequency measurement. Journal articles and books are cited for the following topics: frequency standards; methods of characterizing performance of clocks and oscillators; time scales, clock ensembles, and algorithms; international time scales; frequency and time distribution; and applications. [The letter E after an item indicates elementary level or material of general interest. The letter I, for intermediate level, indicates material of somewhat more specialized nature, and the letter A indicates rather specialized or advanced material. The designations E/I and I/A are used to indicate that the article contains material at both levels, so that at least part of the article is written at the lower of the two levels.]

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 317-330
Inexpensive laser cooling and trapping experiment for undergraduate laboratories
Carl Wieman
Gwenn Flowers

Joint Institute for Laboratory Astrophysics and Department of Physics, University of Colorado, Boulder, Colorado 80309
Sarah Gilbert
National Institute of Standards and Technology, Boulder, Colorado 80303
(Received 14 July 1994; accepted for publication 15 December 1994)
We present detailed instructions for the construction and operation of an inexpensive apparatus for laser cooling and trapping of rubidium atoms. This apparatus allows one to use the light from low power diode lasers to produce a magneto-optical trap in a low pressure vapor cell. We present a design which has reduced the cost to less than $3000 and does not require any machining or glassblowing skills in the construction. It has the additional virtues that the alignment of the trapping laser beams is very easy, and the rubidium pressure is conveniently and rapidly controlled. These features make the trap simple and reliable to operate, and the trapped atoms can be easily seen and studied. With a few milliwatts of laser power we are able to trap 4(times)10[sup 7] atoms for 3.5 s in this apparatus. A step-by-step procedure is given for construction of the cell, setup of the optical system, and operation of the trap. A list of parts with prices and vendors is given in the Appendix. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 330-338
Atoms in orthogonal electric and magnetic fields: A comparison of quantum and classical models
Robert C. Hilborn

Department of Physics, Amherst College, Amherst, Massachusetts 01002
(Received 19 July 1994; accepted for publication 28 October 1994)
The well-known Zeeman and Stark effects can lead to unusual atomic state dynamics when both magnetic and electric fields are present. In this paper we analyze quantum mechanical and classical models of the time evolution of the angular momentum of an atom in the presence of weak, orthogonal electric and magnetic fields. The anisotropic electric polarizability of the atom plays a crucial role in the dynamics. The classical model leads to nonlinear evolution equations, and we investigate how quantum mechanics ``avoids'' the nonlinearity. Finally, we note that the classical equations of motion are identical to those used to describe the time evolution of Stokes vectors for polarized light propagating in an optically nonlinear medium. The treatment is appropriate for an undergraduate course in quantum mechanics. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 339-350
Poincare's proof of the quantum discontinuity of nature
Jeffrey J. Prentis

Department of Natural Sciences, University of Michigan-Dearborn, Dearborn, Michigan 48128
(Received 24 June 1994; accepted for publication 7 October 1994)
In his last memoir on mathematical physics, Henri Poincare presented one of the most profound and compelling proofs of the hypothesis of quanta. This highly original proof, which is actually three separate proofs, is based on first principles and is full of physical insight, mathematical rigor, and elegant simplicity. The memoir is refreshingly uncluttered by some of the conventional, and more abstract concepts, such as temperature and entropy, that Planck and others relied on in their work. Poincare's analysis is based on an ingenious physical model consisting of long-period resonators interacting with short-period resonators. A unique formulation of statistical mechanics, based on the calculus of probabilities, Fourier's integral, and complex analysis, logically unfolds throughout the memoir. Poincare invents an ``inverse statistical mechanics'' that allows him to prove a crucial result that no one had proved before: The hypothesis of quanta is both a sufficient and a necessary condition to account for Planck's law of radiation. In a separate, more universal proof, Poincare proves that the existence of a discontinuity in the motion of a resonator is necessary to explain any observed law of radiation. Given the significant impact of Poincare's memoir on quantum theory and statistical physics, it is surprising that most physicists are not aware of its valuable mathematical and physical ideas. Poincare's tour de force proofs are presented here in a form suitable for use in a standard course in quantum mechanics, statistical mechanics, or mathematical physics. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 351-359
Ball on a rotating turntable: Comparison of theory and experiment
Robert Ehrlich
Jaroslaw Tuszynski

George Mason University, Fairfax, Virginia 22030
(Received 31 May 1994; accepted for publication 18 October 1994)
We have extended the work of others in developing a model for the motion of a ball on a rotating turntable. The numerical model does not impose the constraint of rolling without slipping, and includes both rolling and sliding friction. Computer output from the model is compared with experimental trajectories obtained from time exposures, and found to be in excellent agreement. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 359-363
Heat, light, and videotapes: Experiments in heat conduction using liquid crystal film
Michael E. Bacon

Department of Physics, National University of Lesotho, Roma, Lesotho
R. M. Wick
P. Hecking
Department of Physics, Thiel College, Greenville, Pennsylvania 16125
(Received 24 May 1994; accepted for publication 18 August 1994)
A range of experiments in heat conduction suitable for upper level undergraduate laboratories are described. The experiments progressively cover situations of increasing theoretical complexity. The experiments are relatively easy to perform and make use of heat sensitive liquid crystal film to measure temperature contours. The initial experiments cover examples of situations where Laplace's equation is applicable and can be used to complement experiments in electrostatics using resistive paper. The remaining experiments extend the investigations to situations where Poisson's equation and the diffusion equation are applicable. In these latter two cases the liquid crystal film serves as the heat conduction medium in addition to its function as a temperature sensor. For the diffusion equation situation a video camera is used in conjunction with the liquid crystal film. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 364-369
Mechanical resonance displaying changes in phase to large audiences
R. Dorner
L. Kowalski
M. Stein

Montclair State University, Upper Montclair, New Jersey 07043
(Received 23 June 1994; accepted for publication 28 September 1994)
This article describes lecture demonstration apparatus for displaying free and forced oscillations of a mechanical system to a large class. The setup described won first prize at the AAPT apparatus competition in August 1994. A Plexiglas blade clamped at one end is magnetically driven by a low-frequency generator(en-dash)amplifier. The frequencies are so low (between 0.2 and 1.2 Hz) that visual observations of displacements are possible. The driving voltage, associated with the force applied, is visualized with a row of 20 light-emitting diodes, a laser pointer projecting displacements, and a photosensor providing sound cues for phase references. Dependence of amplitude and phase on frequency can be seen, heard, and recorded by a large group of students. The apparatus is simple enough to be replicated and used at all levels of physics teaching. Technical details on the LED display unit, and some theoretical considerations, are described in two appendices. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 369-376
Ideal quantum gases in two dimensions
S. Viefers
F. Ravndal
T. Haugset

Institute of Physics, University of Oslo, P.O. BOX 1048, Blindern, N-0316 Oslo, Norway
(Received 2 June 1994; accepted for publication 15 September 1994)
Thermodynamic properties of nonrelativistic bosons and fermions in two spatial dimensions and without interactions are derived. All the virial coefficients are the same except for the second, for which the signs are opposite. This results in the same specific heat for the two gases. Existing equations of state for the free anyon gas are also discussed and shown to break down at low temperatures or high densities. (Copyright) 1995 American Association of Physics Teachers.

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 377-379
A simple circuit for demonstrating regular and synchronized chaos
Thomas L. Carroll

Naval Research Laboratory, Washington, D.C. 20375
(Received 29 June 1994; accepted for publication 27 September 1994

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 380-381
Hostages of Each Other: The Transformation of Nuclear Safety since Three Mile Island
Joseph V. Rees
Marc Eisner

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 381-382
Waves Called Solitons: Concepts and Experiments
M. Remoissenet
J. A. Whitehead

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 382-383
Energy, Physics and the Environment
Ernest L. McFarland
James L. Hunt
J. L. Campbell
Ruth H. Howes

Am. J. Phys., Vol. 63, No. 4, April 1995 Pages 383-384
QED and the Men Who Made It: Dyson, Feynman, Schwinger, and Tomonaga
Silvan S. Schweber
Felix M. H. Villars

For more information please send a mail to Dan.MacIsaac@nau.edu.