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Sep 1994

Volume 62, Issue 9, pp. 775-863

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Weightful versus weightless

Frank O. Goodman

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 775 | Cited 1 time

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01.40.G- Curricula and evaluation

Why optical diffraction is ‘‘semiclassical’’

S. A. Fulling

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 775

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42.25.Fx Diffraction and scattering
03.65.Nk Scattering theory

Teaching of special relativity

George F. R. Ellis and Ruth M. Williams

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 775

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01.40.G- Curricula and evaluation
03.30.+p Special relativity

The jerk redux

T. R. Sandin

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 775

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45.05.+x General theory of classical mechanics of discrete systems
01.40.G- Curricula and evaluation

Mere coincidence?

Holger Friedrich

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 776

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01.65.+g History of science
01.75.+m Science and society
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Guest Comment: A generation lost?

Nicholas B. Tufillaro

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 777

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01.75.+m Science and society
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A plane wave approach to particle beam magnetic resonance

R. Golub, R. Gähler, and T. Keller

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 779 | Cited 16 times

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We present a quantum mechanical treatment of particle beam magnetic resonance and related experiments, in terms of static plane waves, applicable to experiments with oscillating fields. The results yield an alternate view of Larmor precession, showing it as a beating between different waves, and help to shed new light on several aspects of the problems discussed. We discuss magnetic resonance experiments with both the Rabi and Ramsey methods, neutron resonance spin echo and a neutron interferometer experiment.
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32.30.Dx Magnetic resonance spectra
76.60.Lz Spin echoes

The observable universe inside a black hole

W. M. Stuckey

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 788

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A Schwarzschild radial coordinate R is presented for the Friedmann dust‐filled cosmology models. It is shown that a worldline of constant Schwarzschild radial coordinate in the dust‐filled universe is instantaneously null at Rn=2GM/c2, where M is the Schwarzschild mass inside the sphere R=Rn. It is also shown that Mp=3τc3/4G, where Mp is the proper mass inside R=Rn and τ is the age of the universe. The Rn=2GM/c2 result in Friedmann dust‐filled cosmology is made physically significant by abandoning the cosmological principle and adjoining segments of Friedmann dust to segments of Schwarzschild vacuum. In the resulting cosmology model, the observable universe may lie inside a black or white hole.
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04.70.Bw Classical black holes
98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology

Implications of cognitive studies for teaching physics

Edward F. Redish

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 796 | Cited 36 times

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01.40.G- Curricula and evaluation

A model to illustrate forces in nuclear fusion

E. Kashy and D. A. Johnson

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 804

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A model consisting of magnets and iron which makes a good analogy of the behavior of the electrostatic and nuclear force involved in the fusion of two protons has been constructed and used as a lecture demonstration. Detailed calculations of the magnetic field and of the forces that explain the unusual behavior of the model are presented. The model can also be useful in electricity and magnetism, where students can be challenged to explain the unusual behavior of this ‘‘science puzzle.’’  
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01.50.My Demonstration experiments and apparatus
21.30.-x Nuclear forces
24.10.-i Nuclear reaction models and methods

Path integral for the motion of a particle in a linear potential

Lowell S. Brown and Yan Zhang

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 806 | Cited 8 times

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The path integral method is used to construct the quantum propagator for a particle moving under a constant force.
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03.65.Ca Formalism

Contextuality in quantum systems

Alberto Clemente de la Torre

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 808 | Cited 2 times

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The logic of the EPR argument is applied, not to two particles in a line but to one particle in a plane. Contextuality (defined here as a generalization of the notion of nonseparability) among commuting observables is shown to emerge as a result, i.e., although the two orthogonal coordinates characterizing the position of a particle commute, nonetheless there are states in which these coordinates are not independent, in the sense that the measurement or observation of one of them must have an effect on the other.
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03.65.Ta Foundations of quantum mechanics; measurement theory

The ‘‘mystery’’ of the quadratic Mandelbrot set

Wolfgang Metzler

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 813

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Numerical simulations suggest that the Mandelbrot set for binary numbers z=x+γy with x, y∊R and γ2=α+γβ (α,β∊R given) is a simple filled‐in square in the perplex case, i.e., α=1, β=0. The paper gives a proof of this experimental result.
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05.45.-a Nonlinear dynamics and chaos
02.30.-f Function theory, analysis

Polygons of unequal resistors

Satinder S. Sidhu

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 815 | Cited 2 times

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Consider an N‐sided polygon made of resistors such that the resistances connected between the vertices are 2G times those connected between the center and each vertex. Effective resistance between the center and a vertex of such a polygon is obtained by a recursive procedure. The limiting value of the resistance for large N is found to be a fraction that is not always irrational. The method developed is suitable even for cases where resistances making up the polygon are of arbitrary values so that conventional symmetry arguments would not be applicable. The results are applied to a uniform wire shaped into a circular wheel with evenly spaced spokes, and other wire frame structures.
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84.30.Bv Circuit theory

Simulator of optimally controlled molecular motion

D. Morris, C. Schwieters, M. Littman, and H. Rabitz

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 817

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This paper presents results of a molecular dynamics simulator (MDS) used to explore optimal control of molecular motion. A realistic model of an interatomic potential is created by a configuration of magnets. This simulated potential approximately models both the short and long range portions of true molecular potentials. Atoms within a polyatomic molecule are simulated using carts which float on an air track and a mechanical driver simulates the action of a controlling laser. In analogy with a molecular system, the potential is determined by analysis of a series of dynamics experiments. Knowledge of the potential combined with optimal control theory enables the design of the driver motion necessary to achieve controlled dissociation. Successful control requires overcoming a variety of difficulties analogous to those expected to be faced in the control of true molecular systems. The MDS provides insight into factors affecting the molecular control by demonstrating a real‐time simulation of laser controlled molecular dynamics.
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82.20.Wt Computational modeling; simulation
02.70.Ns Molecular dynamics and particle methods
01.50.My Demonstration experiments and apparatus

Electrostatic orrery for celestial mechanics

Ted Biewer, David Alexander, Scott Robertson, and Bob Walch

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 821 | Cited 8 times

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A device is described in which negatively charged submillimeter particles are trapped in orbits about a rod with a positive potential. Hollow glass microspheres about 50 μm in diameter are dropped past an emitting filament and accumulate a charge of approximately 5×105 electrons. The microspheres fall into a Kingdon trap (concentric cylinders with end caps) and are trapped by a rising potential of order 10 kV. The orbital decay time is determined by molecular drag and is about 40 min or 105 revolutions at 2×10−6 Torr. Orbiting particles are visible to the unaided eye and may be recorded photographically with a CCD camera. Possible applications from celestial mechanics include experiments on orbital resonances, Kirkwood gaps, and planetary ring phenomena.
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95.10.Eg Orbit determination and improvement
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
01.50.My Demonstration experiments and apparatus

Fields from multipole moment distributions with spherical symmetry: The Fermi contact interaction

Michael J. Harrison and Robert D. Spence

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 828

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We first prove an elementary generalization of Gauss’ law for spherically symmetric distributions of multipole moment density, and then apply our result to derive the Fermi contact hyperfine interaction between the electron spin magnetism of s state electrons and nuclear magnetic moments.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
31.30.Gs Hyperfine interactions and isotope effects

Student evaluation of computer‐based instruction in a large university mechanics course

Lorella M. Jones and Dennis J. Kane

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 832

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Students in a large freshman mechanics course for engineers use computer‐based tutorials, homework exercises, and quizzes as an important part of the course. For 27 consecutive semesters, students were asked to rate various course components on their usefulness in learning the material. In every one of these semesters, the computer‐based materials outranked the lecturer, text, and lab section—despite the fact that lecturers and texts varied.
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01.50.ht Instructional computer use
01.40.G- Curricula and evaluation

Geometrical derivation of Lagrange’s equations for a system of particles

James Casey

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 836 | Cited 9 times

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A concise but general derivation of Lagrange’s equations is given for a system of finitely many particles subject to holonomic and nonholonomic constraints. Based directly on Newton’s second law, it takes advantage of an inertia‐based metric to obtain a geometrically transparent statement of Lagrange’s equations in configuration space. Illustrative examples are included.
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45.05.+x General theory of classical mechanics of discrete systems
02.40.Ky Riemannian geometries

Solvable model for inelastic collisions

J. G. Muga and R. F. Snider

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 848 | Cited 2 times

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An analytically solvable model is described for the inelastic collision of two particles moving in one dimension but having an orientation dependent interaction. The bound states and scattering matrix for this system are explicitly calculated.
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11.80.-m Relativistic scattering theory
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Brewster’s law and a hazard of volume integration over molecular scatterers

Robert R. Turtle

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 853

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Abstract Unavailable
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42.25.Ja Polarization
78.20.Bh Theory, models, and numerical simulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Comment on ‘‘Chaos in a computer‐animated pendulum,’’ by R. L. Kautz [Am. J. Phys. 61, 407–415 (1993)]

Daniel R. Frankl

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 854

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01.50.ht Instructional computer use
05.45.-a Nonlinear dynamics and chaos

Erratum: ‘‘Photoemission energy distribution measurements in a simple metal. A modern physics undergraduate laboratory’’ [Am. J. Phys. 61 (12), 1114–1118 (1993)]

Rosalia Zangara and Elisa Lanzara

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 855

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01.50.Pa Laboratory experiments and apparatus
79.60.-i Photoemission and photoelectron spectra
99.10.Cd Errata
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Colorful demos with a long‐lasting soap bubble

F. Behroozi and D. W. Olson

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 856 | Cited 2 times

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Abstract Unavailable
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01.50.My Demonstration experiments and apparatus
78.66.-w Optical properties of specific thin films

Measurement of liquid crystal refractive indices

Devanand K. Shenoy

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 858 | Cited 2 times

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It is shown that a student spectrometer may be modified easily to measure the anisotropic refractive indices of liquid crystals.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

Transparency film for demonstration of biaxial optics

Paul R. Camp

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 859

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01.50.My Demonstration experiments and apparatus
78.66.-w Optical properties of specific thin films
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A First Course in Computational Physics

Paul L. DeVries, Author and Harvey Gould

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 861

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Abstract Unavailable
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01.30.mp Textbooks for undergraduates
02.70.-c Computational techniques; simulations

Chaos and Nonlinear Dynamics: An Introduction for Scientists and Engineers

Robert C. Hilborn, Author and J. C. Sprott

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 861

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Abstract Unavailable
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01.30.mp Textbooks for undergraduates
01.30.mm Textbooks for graduates and researchers
05.45.-a Nonlinear dynamics and chaos

Science and Anti‐Science

Gerald Holton, Author and Henry H. Bauer

American Journal of Physics -- September 1994 -- Volume 62, Issue 9, pp. 862

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.75.+m Science and society
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