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Aug 1981

Volume 49, Issue 8, pp. 711-799

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Letter to the Editor (with reply)

Arthur Eisenkraft and John S. Rigden

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 711

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Abstract Unavailable
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01.75.+m Science and society

Sports and physics

M. A. R. P. de Barros

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 711

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Abstract Unavailable
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01.40.G- Curricula and evaluation

Brief derivations of relativistic mass

N. Gauthier

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 712

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03.30.+p Special relativity
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Editorial: Gerald Holton—physicist and humanist

John S. Rigden, Editor

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 713

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01.60.+q Biographies, tributes, personal notes, and obituaries
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Thermodynamics of blackbody radiation

Robert E. Kelly

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 714 | Cited 6 times

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The thermodynamics of homogeneous, isotropic, unpolarized electromagnetic radiation in a cavity with volume and temperature controllable as the independent variables is analyzed. Internal energy, pressure, chemical potential, enthalpy, Gibbs free energy, heat capacities, expansivity, and compressibility are all derived from the Helmholtz free energy. Topics treated are the third law, isothermal, adiabatic, and free expansion, throttling process, phase equilibrium, stability, and the Carnot cycle.
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05.70.-a Thermodynamics

Surface properties of Kerr–Newman black holes

Noel A. Doughty

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 720

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The magnitude of the proper acceleration of a stationary observer in the exterior Kerr–Newman geometry is used to determine an elementary property of the event horizon of a rotating charged black hole and to give a simple physical interpretation of its ’’surface gravity’’ as used in descriptions of the Hawking radiation. The global (nonlocal) nature of a black hole event horizon is also simply illustrated. The Kerr–Newman metric and the calculations based on it are presented in SI equations for the benefit of the many students and teachers in physics who rarely use any other system. To minimize the mathematical tools required we carry out the calculations in the well‐understood Boyer–Lindquist coordinates.
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97.60.Lf Black holes
97.10.Pg Radii
97.10.Qh Surface features (including starspots)
95.30.Sf Relativity and gravitation

Physics of living in space: A new course

C. H. Holbrow

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 725

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A new course uses the prospect of living in space to motivate students to learn some basic physics and also to grapple with some larger questions about the differences between pure science and technology. Among the special features of this course are a set of exercises (two done with a computer graphics terminal), a treatment of dynamics that defines mass from the conservation of momentum rather than from Newton’s second law of motion, and a strong emphasis on weightlessness, rocket propulsion, orbital mechanics, and other aspects of physics relevant to how one might build an orbiting city in space and live there.
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01.40.Di Course design and evaluation
07.87.+v Spaceborne and space research instruments, apparatus, and components (satellites, space vehicles, etc.)
01.55.+b General physics

Hall effect in a plasma

W. B. Kunkel

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 733 | Cited 1 time

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In low‐density plasmas, such as the positive columns of glow discharges, the Hall effect is very large and easily observable. An elementary analysis, reproduced here, shows that the Hall voltage between opposite sides of such a column measures only half of that expected ideally in a conductor with the same carrier density. The reduction is caused by ambipolar diffusion of the carriers whose density distribution is distorted in the presence of a transverse magnetic field. A simple experimental arrangement is described in which the Hall voltage across a helium discharge column is determined as a function of magnetic field, discharge current, and gas pressure. Thus electron drift velocity and density are inferred. A simultaneous measurement of the resistivity then permits evaluation of the collision frequency. If the collision cross section for scattering of electrons by helium atoms is given, the electron temperature can be estimated. Variation of the parameters thus permits a study of the scaling laws for the glow discharge column. The experiment is found to be a very rewarding educational experience.
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52.80.Hc Glow; corona
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

Illustrating gauge invariance in quantum mechanics through the free electron in a uniform time‐varying electric field

C. Leubner

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 738 | Cited 4 times

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The nature of gauge transformations and gauge invariance in quantum mechanics about which there exists so much confusion in the literature is simply and pedagogically illuminated by first carefully investigating in various gauges the elementary problem of a free electron subject to a spatially uniform time‐dependent electric field, and by then utilizing the findings from this particular example to clarify some general misconceptions.
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03.65.-w Quantum mechanics

Euler angles, direction cosines, and angular momentum

Flemming Jørgensen

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 744

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The line of nodes en for the Euler angles (ϕ, ϑ, χ) is orthogonal to the plane of the two z axes e°z and ez. In the present paper we introduce two vectors, f°z and fz, in the plane of the z axes such that the set (f°z, en, fz) is biorthogonal to (e°z, en, ez). These new vectors are so easily visualized that their components can be written down by inspection of the figure illustrating the definition of the Euler angles, and thus the direction cosine e°r ⋅ es can be obtained simply. This derivation makes no use of matrices. The total angular momentum J for a system of particles, where the Euler angles are used as coordinates for overall rotation, is shown in a simple manner to be J = f°zpϕ+enpϑ+fzpχ,@qL where (pϕ, pϑ, pχ) are the momenta conjugate to (ϕ, ϑ, χ).
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45.05.+x General theory of classical mechanics of discrete systems

Fourier integral treatment yielding insight into the control of Gibb’s phenomenon

James E. Harvey

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 747

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The phenonmenon of overshoot and the associated oscillation (Gibb’s phenomenon) that occur in the Fourier series approximation to a discontinuous function are investigated by considering the Fourier sum to be a special case of the Fourier integral transform. It is then shown that Gibb’s phenomenon can be reduced or eliminated by multiplying the Fourier transform of the desired function by an appropriate filter function; however, this also reduces the steep slopes representing the points of discontinuity. Two separate parameterized filter functions are presented that can be used in trade‐off studies to optimize the magnitude of the resulting oscillations and reduction in slope associated with the discontinuity.
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02.30.Nw Fourier analysis
02.30.Lt Sequences, series, and summability
02.30.Uu Integral transforms
02.30.Vv Operational calculus

Physical approach to the theory of constrained motion

Shu‐Ping Liu

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 750 | Cited 2 times

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A mathematically elementary approach based entirely on Newton’s laws of motion and physical arguments to the problem of constrained motion subjected to general velocity‐dependent constraints is presented. Natures of constraint forces are extracted from constraint relations and, consequently, the equations of motion in Newton’s, Lagrange’s, and Appell’s form are obtained. D’Alembert’s principle is proved to be true for and only for holonomic constraints and constraints homogeneous in velocity dependence.
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45.05.+x General theory of classical mechanics of discrete systems

Quantum operators in generalized coordinates

Pedro Villaseñor‐González and Joel Cisneros‐Parra

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 754

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It will be shown in this paper how to build quantum operators in generalized coordinates. A direct substitution of momentum operators in the classical expression suffices; the only condition being that this expression must be written in matrix form before the substitution. Specifically, we are then able to show that the two operators −ih̸(∂/∂Q) and −ih̸g−1/2 (∂/∂Q)g1/2, and only these, are to be associated with generalized momenta.
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03.65.Ca Formalism
02.30.Tb Operator theory

The cat landing on its feet revisited or angular momentum conservation and torque‐free rotations of nonrigid mechanical systems

Hanno Essén

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 756 | Cited 1 time

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This paper explains the connection between rotation and the law of conservation of angular momentum and points out that macroscopic angular momentum need not be conserved if it can be transferred to spin. Exact equations giving the rotational motion induced by a given internal motion are derived and discussed.
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87.19.rs Movement
87.19.ru Locomotion
45.05.+x General theory of classical mechanics of discrete systems

The pendulum reborn: Time measurements in the teaching laboratory

Maurice Bazin and Pierre Lucie

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 758

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To oppose the trend towards a formal, purely theoretical teaching of physics we present our first practical step at creating a lively laboratory practice at the first‐year university physics level in Brazil. Two pendula are used simultaneously as the system under study and the time measuring reference instrument. We describe how we integrate historical and cultural references within our laboratory practice.
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01.50.Pa Laboratory experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems
06.30.Ft Time and frequency

Simple explanation of a well‐known collision experiment

F. Herrmann and P. Schmälzle

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 761 | Cited 8 times

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A well‐known collision experiment can be carried out with an arrangement of several identical elastic balls each suspended by two threads and in contact with one another: a certain number of the balls is displaced from its equilibrium position and then released, so as to collide with the remaining balls at rest. After the collision, the same number of balls moves away to the other side as had initially been displaced. It is shown that, contrary to common belief, the conservation laws of energy and momentum alone are not sufficient to explain this behavior. Indeed, a further condition must be satisfied by the system of balls; namely, it must be capable of dispersion‐free energy propagation.
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01.55.+b General physics
45.05.+x General theory of classical mechanics of discrete systems

Hydrogenlike atom in the potential V = r2(a+b cos2θ): Second‐order perturbation theory

Basab B. Dasgupta

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 764

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We report a calculation of the ground‐state energy of a hydrogenlike atom in an external potential given by V = r2(a+b cos2ϑ), using the second‐order perturbation theory. The matrix elements, involving both the bound‐state and continuum‐state eigenfunctions, are explicitly evaluated. Implication of the result in the magnetic study of quasi‐two‐dimensional electron layers on a liquid‐helium surface is discussed.
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03.65.-w Quantum mechanics

Modern spectroscopy with a spectrometer by the optogalvanic effect

Kenneth Arnett, Richard Anderson, and Ralph Alexander

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 767 | Cited 2 times

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An experiment involving the optogalvanic effect suitable for the advanced physics laboratory is described. This experiment complements the usual basic experiment in atomic spectroscopy where spectra are recorded on photographic film with a spectrograph or with a monochromator and photomultiplier. The optogalvanic effect used the atoms being studied as the detector and a tunable dye laser as the source. Linewidths observed are those of the dye laser that are considerably smaller than those obtained with the usual laboratory monochromator. The student is introduced to the techniques of spectroscopy with pulsed dye lasers and to a spectrum for which LS coupling does not hold.
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01.50.Pa Laboratory experiments and apparatus
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

Singly refracting biaxial crystals: A curiosity in Maxwell’s electrodynamics

G. P. Sastry and D. Chowdhury

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 773 | Cited 1 time

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The little‐known fact that a biaxial crystal with a tensor permittivity ϵij as well as a tensor permeability μij can have a single refracted extraordinary ray for arbitrary angles of incidence on arbitrary cuts of the crystal, provided it satisfies the material condition ϵ1/μ1 = ϵ2/μ2 = ϵ3/μ3, is demonstrated from first principles and the consequences are examined in some detail.
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78.20.Ls Magneto-optical effects
75.30.-m Intrinsic properties of magnetically ordered materials

Flashlamp‐pumped dye laser as an undergraduate lab project

Anthony J. Alfrey

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 776 | Cited 1 time

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State‐of‐the‐art dye lasers have been exhaustively discussed previously in the literature, however, few of these articles provide the essential bare details necessary to construct a simple working dye laser. This discussion presents an overview of the construction techniques of dye lasers suitable for student projects. Ease in construction, low cost, and tuneable output in the visible range make such lasers ideal for the junior‐level lab. Skills required to complete a dye laser include basic optics, electricity, and modern physics usually covered at the sophomore level.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
01.50.Pa Laboratory experiments and apparatus
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Coriolis force revisited

Jacob Neuberger

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 782

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The author shows that if air resistance is proportional to the velocity, the Coriolis projectile problem is solved.(AIP)
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45.05.+x General theory of classical mechanics of discrete systems

Comparative reasoning abilities of college students

David P. Maloney

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 784 | Cited 3 times

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Comparative reasoning abilities of college students, based on an application of Piagetian theories, are discussed with to different populations of students.(AIP)
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01.40.G- Curricula and evaluation

Computing the moment of inertia

Russell Patera

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 786

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The author presents a method for computing the moment of inertia of an extended body without the use of calculus for a specific class of geometrical shapes. (AIP)
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45.05.+x General theory of classical mechanics of discrete systems

Abbe’s sine theorem from a thermodynamic and Fourier transform argument

Jack Higbie

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 788

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Abbe’s sine theorem of geometrical theory of lens aberrations is considered by thermodynamics and Fourier transform arguments.(AIP)
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42.79.Bh Lenses, prisms and mirrors

Diffraction grating as a model of the incommensurate phase

V. Rutar and J. Seliger

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 789

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The author shows a special diffraction grating can be used as a model of the incommensurate phase of a crystal. (AIP)
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42.79.Dj Gratings
05.70.Fh Phase transitions: general studies
61.05.F- Neutron diffraction and scattering

Computer projects in physics: A course

J. D. Patterson

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 791

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The development of a physics course that makes use of computer facilities is discussed. (AIP)
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01.50.ht Instructional computer use
01.40.Di Course design and evaluation

Comments on Fourier analysis of the simple pendulum

Donald E. Hall

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 792 | Cited 1 time

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The author offers observations on comments recently made by Simon and Riesz concerning a simple pendulum. (AIP)
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45.05.+x General theory of classical mechanics of discrete systems
02.30.Lt Sequences, series, and summability

Erratum: ’’Resource Letter SP‐2: Symmetry and group theory in physics’’ [Am. J. Phys. 49, 304 (1981)]

Joe Rosen

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 793

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Abstract Unavailable
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01.30.Rr Surveys and tutorial papers; resource letters
11.30.-j Symmetry and conservation laws
02.20.-a Group theory
99.10.Cd Errata
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Novel demonstration of total internal reflection

D. C. Look, Jr.

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 794

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Abstract Unavailable
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01.50.Pa Laboratory experiments and apparatus
42.25.Gy Edge and boundary effects; reflection and refraction
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Encyclopedia of Physics

Rita G. Lerner, Editor, George L. Trigg, Editor, and John S. Rigden

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 795

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.50.-i Educational aids

Wholeness and the Implicate Order

David Bohm, Author and David Park, Reviewer

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 796

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.70.+w Philosophy of science
03.65.Ta Foundations of quantum mechanics; measurement theory
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Rainbow I: Ancient and Medieval and Rainbow II: Light and Color (film)

Samuel Devons, Producer and Bruce Eastwood

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 798

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Abstract Unavailable
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01.50.F- Audio and visual aids
42.25.Gy Edge and boundary effects; reflection and refraction
42.68.-w Atmospheric and ocean optics

It’s About Time (film)

WGBH Educational Foundation Producer and R. H. Good, Reviewer

American Journal of Physics -- August 1981 -- Volume 49, Issue 8, pp. 798

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Abstract Unavailable
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01.50.F- Audio and visual aids
06.30.Ft Time and frequency
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