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Dec 1994

Volume 62, Issue 12, pp. 1063-1157

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Coriolis myths and draining bathtubs

John W. Hanneken

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1063

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47.32.-y Vortex dynamics; rotating fluids

More on Coriolis myths and draining bathtubs

Richard R. Hake

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1063

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47.32.-y Vortex dynamics; rotating fluids

Still more on Coriolis myths and draining bathtubs—films and video tapes

Charles Robertson

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1063

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47.32.-y Vortex dynamics; rotating fluids
01.50.F- Audio and visual aids

Galileo to Malthus—the Catholic perspective

Robert C. Amme

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1064

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01.75.+m Science and society

Left‐handed and right‐handed coordinate systems

Theodore E. David

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1064 | Cited 1 time

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01.40.G- Curricula and evaluation
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Editorial: A report to the readers—and a request for suggestions

Robert H. Romer

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1065 | Cited 1 time

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01.10.Hx Physics organizational activities
01.30.-y Physics literature and publications
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21 cm line of atomic hydrogen

J. W. V. Storey, M. C. B. Ashley, M. Naray, and J. P. Lloyd

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1077

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Discovered in 1951, the 21 cm hyperfine line of atomic hydrogen has become one of the best‐studied spectral features in radioastronomy. Used to trace the distribution and velocity of atomic gas in our own and in other galaxies, the line has made an enormous contribution to our understanding of galactic structure. Now, 40 years after the line’s discovery, a low‐cost receiving system can be assembled from items of consumer electronics to enable study of the line in an undergraduate laboratory.
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31.30.Gs Hyperfine interactions and isotope effects
98.58.Ge H I regions and 21-cm lines; diffuse, translucent, and high-velocity clouds

Further thoughts on Newton’s zero‐order rainbow

James A. Lock and Timothy A. McCollum

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1082 | Cited 8 times

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A zero‐order rainbow angle may be defined as the relative minimum angle of deviation of geometrical light rays transmitted without internal reflections through a transparent particle. If the incident rays are parallel and the particle is a sphere, such a minimum does not exist. But if the incident rays are not parallel or if the particle has an elliptical rather than circular cross section, an angle of minimum deviation, hence a zero‐order rainbow, can occur. For a spherical water droplet, the zero‐order rainbow will occur when a point source is placed less than a droplet radius away from its surface. If a column of water with an elliptical cross section is illuminated by a plane wave, a zero‐order rainbow will occur if the length of the major axis of the cross section is more than twice the length of the minor axis.
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42.15.Fr Aberrations
42.25.Gy Edge and boundary effects; reflection and refraction

Max Planck and the ‘‘black year’’ of German physics

Joseph F. Mulligan

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1089

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1994 is the hundredth anniversary of what Max Planck described in 1935 as the ‘‘black year’’ of German physics. In the eight months between January 1st and September 8th 1894, Heinrich Hertz, August Kundt, and Hermann von Helmholtz died. This article reviews the lives of these three important physicists, their research contributions, and their unique positions in the German physics community. In conclusion, the relationships of these three physicists to Planck are discussed, and Planck’s evaluation of the impact of 1894 on physics in Germany is appraised from our perspective of one hundred years.
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01.60.+q Biographies, tributes, personal notes, and obituaries
01.65.+g History of science

A simple, conservative understanding of many time‐driven systems

Harvey Kaplan

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1097

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Examination of two alternative models of a bead sliding on a rotating circular wire reveals the meaning of a conserved Hamiltonian where it is not the total energy. Analogies to other such dual treatments are discussed.
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45.05.+x General theory of classical mechanics of discrete systems

The circular disk parallel plate capacitor

G. T. Carlson and B. L. Illman

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1099 | Cited 9 times

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One of the more familiar systems in electrostatics is the parallel plate capacitor (PPC). While this system has received considerable attention in the close plate approximation, little is known about the exact solution for arbitrary plate separations. Although the solution was first given, in cylindrical coordinates by Sneddon, it was part of a more general treatise on mixed boundary value problems and appears to be unknown to much of the physics community. We present here a dedicated derivation of the solution to the boundary value problem for parallel disks, in cylindrical coordinates. The resulting expressions for potential and capacitance are in closed form, but depend on a function f(t) which is determined from an integral equation of the Fredholm type, known as Love’s equation. By adopting an orthogonal series approach to the solution of Love’s equation, we have calculated the capacitance for a number of plate separation to plate radius ratios. A quantitative measure of the close plate approximation is then presented by comparing these values to those one would obtain using the elementary capacitance equation ϵ0A/d.
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84.32.Tt Capacitors
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Kamerlingh Onnes and the discovery of superconductivity

Paul H. E. Meijer

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1105 | Cited 1 time

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Many papers begin with the statement that Kamerlingh Onnes discovered superconductivity in 1911; one wonders what urged him to do the experiment that led to this discovery. Superconductivity was definitely not foreseen at that moment, and for many years the theory could not even predict it. Hence what drove Kamerlingh Onnes to measure the electrical resistivity at a temperature range where one could not expect to find anything radically new? What were the prevailing theories at that time? This is discussed after a general description of the man, his laboratory, and the state of physics in the preceding years. Conclusion: Although the driving factor in the low temperature resistance work was most likely the need for a reliable and reproducible thermometer, the speculations about what would happen in these regions were based on Kelvin’s theory, at least in the initial phase of the work. This theory predicted exactly the opposite of what was found eventually.
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01.60.+q Biographies, tributes, personal notes, and obituaries
01.65.+g History of science

Radiation fields of a dipole in arbitrary motion

José A. Heras

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1109 | Cited 7 times

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We present a version of Jefimenko’s formulas for electric and magnetic fields in material media, and we demonstrate how this version of the formulas may be used for deriving the electric and magnetic fields produced by an arbitrarily moving dipole containing both electric and magnetic moments. Like the fields produced by a charge in arbitrary motion, the fields of an arbitrarily moving dipole can also be written in two forms: The Heaviside–Feynman form and the Liénard–Wiechert form. We derive here the first form and the radiation fields associated with the second form. These radiation fields are expressed by means of concise, symmetric, and illuminating formulas.
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03.50.De Classical electromagnetism, Maxwell equations

Hellmann–Feynman theorem in a linear superposition of energy eigenstates

S. Balasubramanian

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1116 | Cited 1 time

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A generalization to the Hellmann–Feynman theorem is presented when the quantum mechanical state is a linear superposition of energy eigenstates. Some simple applications are discussed.
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03.65.Ca Formalism

An electrostatic problem: A point charge outside a prolate dielectric spheroid

Dragan V. Redžić

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1118

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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Remarkable shapes of a catenary under the effect of gravity and surface tension

F. Behroozi, P. Mohazzabi, and J. P. McCrickard

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1121 | Cited 3 times

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The shape assumed by a hanging chain (the catenary) has been known for 300 years, since Leibnitz first published the correct equation of the catenary around 1690. We have investigated the shape of a hanging string when the area bounded by the string and the supporting rod is covered by a soap film. The competition between the surface tension and the normal component of the gravitational force per unit length determines the shape assumed by the hanging string. When the surface tension is dominant, the string assumes a convex shape similar to the Greek letter gamma. When gravity dominates, the shape is a distorted catenary. In the special case when the surface tension is exactly balanced by the normal component of the gravitational force per unit length, the string assumes a linear shape like the letter V. In this article the governing differential equations are derived for the general case and solved analytically to yield a pair of parametric equations for the x and y coordinates, describing the shape of the string. Numerical results based on these equations account very well for all the experimental features described above.
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68.03.Cd Surface tension and related phenomena

Amount of night sky at any place at any time of year

P. K. Aravind

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1129

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The composition of the night sky, as well as its quantity, change slowly throughout the course of the year. While the change in the appearance of the night sky from season to season is familiar to most amateur astronomers, the amount of sky that can be seen during any night is hardly ever remarked upon (apart from the general statement that there is more sky to be seen in winter because the nights are longer). In this paper I use elementary vector methods to calculate the total solid angle of sky (in steradians) seen in the course of the night at any place (latitude) on any day of the year. The results are compared with the duration of night at that location throughout the year. The effect of twilight on these estimates is also considered.  
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95.10.Ce Celestial mechanics (including n-body problems)

Compact complex expressions for the electric field of two‐dimensional elliptical charge distributions

Miguel A. Furman

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1134 | Cited 1 time

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We present a formula for the analytic calculation of the electric field in complex form for two‐dimensional charge distributions with elliptical contours, in the absence of boundary conditions except at infinity. The formula yields compact and practical expressions for a significant class of distributions. The fact that the electric field vanishes inside an elliptical shell follows as a straightforward consequence of Cauchy’s theorem. The known expressions for the field inside and outside a uniformly charged ellipse are recovered in simple, concise form. Similarly, the expression for the field of a Gaussian distribution is found in a straightforward way as a special case of the more general formula. We also present a brief discussion of more complicated distributions.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
02.30.-f Function theory, analysis

The square wheel revisited

L. Takacs

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1141

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The dynamics of the square wheel is re‐evaluated. It is shown that the minimum coefficient of static friction required for pure rolling decreases from 1 for very slow motion to only 0.105 at the optimum kinetic energy, then increases again for faster motion. The kinetic energy and the equations of motion are derived considering translation of the center of mass and rotation about it in an inertial coordinate system attached to the roadbed and also for rotation about the point of contact. The fact that the instantaneous axis of rotation is accelerating is emphasized and its consequences are discussed.  
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45.05.+x General theory of classical mechanics of discrete systems

Once more the perturbed Kepler problem

A. A. Stahlhofen

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1145 | Cited 3 times

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A qualitative description of Kepler problems perturbed by external fields is presented using only the tools of elementary mechanics. All considerations can be based on a nonconserved Runge–Lenz vector. A transfer of these methods to related classical or quantum‐mechanical problems is possible.
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45.05.+x General theory of classical mechanics of discrete systems
03.65.Sq Semiclassical theories and applications
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Simple proof that energy stored in a magnetic field is proportional to the magnitude of the field induction squared

C. D. Popov

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1148

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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Comment on ‘‘Dust off the neutron howitzer to teach nuclear physics!,’’ by J. L. DuBard and A. Gambhir [Am. J. Phys. 62, 255–257 (1994)]

Stephen C. Yerian

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1150 | Cited 2 times

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01.50.Pa Laboratory experiments and apparatus
29.30.Kv X- and γ-ray spectroscopy

Comment on ‘‘Entropy production and the second law of thermodynamics: An introduction to second law analysis,’’ by Thomas V. Marcella [Am. J. Phys. 60 (10), 888–895 (1992)]

S. K. Das

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1151

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05.70.Ce Thermodynamic functions and equations of state
01.50.-i Educational aids
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Theory and Experiment in Gravitational Physics

Clifford M. Will, Author and James L. Anderson

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1153

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01.30.Ee Monographs and collections
01.30.mm Textbooks for graduates and researchers
04.80.-y Experimental studies of gravity

The Quantum Vacuum: An Introduction to Quantum Electrodynamics

Peter W. Milonni, Author and Claudia Eberlein

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1154

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01.30.mm Textbooks for graduates and researchers
12.20.-m Quantum electrodynamics

The Beat of a Different Drum: The Life and Science of Richard Feynman

Jagdish Mehra, Author and Helge Kragh

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1155

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01.30.Ee Monographs and collections
01.60.+q Biographies, tributes, personal notes, and obituaries
01.65.+g History of science

From Alchemy to Quarks: The Study of Physics as a Liberal Art

Sheldon L. Glashow, Author and A. John Mallinckrodt

American Journal of Physics -- December 1994 -- Volume 62, Issue 12, pp. 1156

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