bluuebunny/crossref_metadata_2025 huggingface dataset:
On the effectiveness of active-engagement microcomputer-based laboratories
Authors: Redish Edward F. , Saul Jeffery M. , Steinberg Richard N.
Published: March 2005

One hour active-engagement tutorials using microcomputer-based laboratory (MBL) equipment were substituted for traditional problem-solving recitations in introductory calculus-based mechanics classes for engineering students at the University of Maryland. The results of two specific tutorials, one on the concept of instantaneous velocity and one on Newton’s third law were probed by using standard multiple-choice questions and a free-response final exam question. A comparison of the results of 11 lecture classes taught by six different teachers with and without tutorials shows that the MBL tutorials resulted in a significant improvement compared to the traditional recitations when measured by carefully designed multiple-choice problems. The free-response question showed that, although the tutorial students did somewhat better in recognizing and applying the concepts, there is still room for improvement.
Wave packet distortion and time delay
Authors: de la Torre Lorenzo
Published: March 2005

The distortion of wave packets in potential scattering is studied, and two characterizations of distortion are proposed. When the energy derivative of the scattering amplitude does not change appreciably over the spectral width of the incident wave packet, the characterizations of distortion produce simple formulas and lead to an interesting connection between distortion and time delay.
Nonlocal character of quantum theory
Authors: Stapp Henry P.
Published: March 2005

According to a common conception of causality, the truth of a statement that refers only to phenomena confined to an earlier time cannot depend upon which measurement an experimenter will freely choose to perform at a later time. According to a common idea of the theory of relativity this causality condition should be valid in all Lorentz frames. It is shown here that this concept of relativistic causality is incompatible with some simple predictions of quantum theory.
A new approach to linear Landau damping
Authors: Brodin G.
Published: March 2005

We present a new description of linear Landau damping of plasma waves. The process is found to be governed by a set of two equations with an energy conservation law that is different from the standard form. An analytical solution containing an explicit expression for the velocity distribution function is given. The effect of different initial conditions is demonstrated numerically. We argue that our new approach has several advantages as compared with the standard presentations of introductory plasma textbooks.
Magnetic dipole oscillations and radiation damping
Authors: Stump Daniel R. , Pollack Gerald L.
Published: March 2005

We consider the problem of radiation damping for a magnetic dipole oscillating in a magnetic field. An equation for the radiation reaction torque is derived, and the damping of the oscillations is described. Also discussed are runaway solutions for a rotating magnetic dipole moving under the influence of the reaction torque, with no external torque.
Velocity measurements through magnetic induction
Authors: Carpena P.
Published: March 2005

A simple experiment based on magnetic induction is presented to measure the velocity of a magnet flying through air using a signal induced by a magnet when it passes through a coil. The results show that some properties of this signal depend only on the geometry of the coil and this fact can easily be applied to obtain the velocity of the magnet.
Optical Doppler measurements
Authors: Belich T. James , Lahm Ryan P. , Peterson Richard W. , Whipple Chad D.
Published: March 2005

Light from a low-cost He–Ne laser is filtered to provide a single-mode beam of long coherence length. Beat frequencies in the 100- to 500-kHz range are produced by superimposing laser radiation and waves which are Doppler shifted by a moving retroreflector. Varying speeds of a model train mounted reflector are independently measured with a photogate and allow a check of the Doppler predicted speed, or the photogate determined speed can be used to measure the laser wavelength by a fit of data points with a resulting standard deviation of less than 0.5% of λ. A frequency to voltage converter allows direct velocity plots for constant acceleration or simple harmonic motion.
Relativistic charged-particle motion in a constant field according to the Lorentz force law
Authors: Hyman Andrew T.
Published: March 2005

A new and simple method is presented for integrating the equations of motion of a classical relativistic particle subject to a Lorentz force, given electromagnetic fields that are constant in space-time. This integration method leads naturally to a manifestly covariant form of solution.
Gravitational expansion and the destruction of a black hole
Authors: Gautreau Ronald , Cohen Jeffrey M.
Published: March 2005

Using methods developed by us in a previous paper on gravitational collapse, we follow the evolution of an expanding spherically symmetric zero-pressure ball of dust that starts its expansion within a black hole. The general relativistic equations for the trajectories of the geodesic particle-clocks measuring our time coordinate follow from an inverse square relation, and are formally identical with equations obtained in Newtonian gravitational theory. Within the expanding body there is an apparent horizon, related to the Schwarzschild radius associated with the trajectory of each particle-clock. Because of the existence of a region of expelled surfaces, bounded on one side by the apparent horizon, we show that the destruction of the black hole is inevitable.
A simpler solution of the Dirac equation in a Coulomb potential
Authors: Goodman Bernard , Ignjatović Siniša R.
Published: March 2005

We present an alternative to the standard method of solution of the Dirac equation for a particle in a Coulomb potential, which hews closer to the more familiar solution of the nonrelativistic Schrödinger equation. The bound-state wave functions so obtained are also closer in form to the nonrelativistic Schrödinger wave functions and make the transition to this limit more evident. The equivalence of these and the “standard” solution form of the Dirac wave functions is demonstrated in the Appendix, which, at the same time, shows the advantage of a new trigonometric parametrization in the algebraic manipulation of relativistic quantities.
The quantum defect: Early history and recent developments
Authors: Rau A. R. P. , Inokuti Mitio
Published: March 2005

The notion of the quantum defect is important in atomic and molecular spectroscopy and also in unifying spectroscopy with collision theory. In the latter context, the quantum defect may be viewed as an ancestor of the phase shift. However, the origin of the term “quantum defect” does not seem to be explained in standard textbooks. It occurred in a 1921 paper by Schrödinger, preceding quantum mechanics, yet giving the correct meaning as an index of the short-range interactions with the core of an atom. We present the early history of the quantum-defect idea, and sketch its recent developments.
Resource Letter: ND-1: Nonlinear Dynamics
Authors: Hilborn Robert C. , Tufillaro Nicholas B.
Published: March 2005

This Resource Letter provides an introductory guide to the literature on nonlinear dynamics. Journal articles and books are cited for the following topics: general aspects of nonlinear dynamics and applications of nonlinear dynamics to various fields of physics, other sciences, and a few areas outside the sciences. Software and Internet resources are given also.
A laboratory experiment with blue light-emitting diodes
Authors: Redondo E. , Ojeda A. , Gonzalez Dı́az G. , Mártil I.
Published: March 2005

We present a laboratory experiment designed to show the main characteristics of blue light-emitting diodes. The analyzed devices are based on III–V nitrides (in which the active layer is a direct band gap In0.06Ga0.94N alloy) and SiC (where the active layer is the 6H polytype of this semiconductor, which is of an indirect band gap class). From the measurements, an In relation could be established between light emission and device current, with n values related to both the physical structure and electroluminescence characteristics of these semiconductors. The spectral response measurements allow us to obtain the peak wavelength of emission with reasonable precision (449±4 nm in the former one and 470±4 nm in the last one). It is also possible to accurately obtain the band gap value of the active layer in the device based on III–V nitrides (3.18±0.03 eV) by analyzing its electroluminescence spectra. However, the same analysis is not possible in the SiC-based device due to its extremely low measured luminous intensity values. A comparison of power conversion efficiency of both devices is also given.
A simplified approach to collision processes
Authors: Ramsey Gordon P.
Published: March 2005

We present an approach to two-body collision processes which simplifies the algebra and leads to a convenient geometrical visualization of these processes in the velocity plane. Special cases, such as the lab and center-of-mass frames, can easily be extracted from the general solutions without further algebra. The geometric interpretation provides insight into the dynamics of collisions without having to consider numerous special cases. Thus important physics concepts can be illustrated without students becoming lost in the algebra.
The linear potential propagator
Authors: Holstein Barry R.
Published: March 2005

The Feynman propagator for the case of a linear potential is evaluated by a variety of means.
An unpublished lecture by Heinrich Hertz: “On the energy balance of the Earth’’
Authors: Mulligan Joseph F. , Hertz H. Gerhard
Published: March 2005

This paper presents a recently discovered and newly translated manuscript of a lecture by Heinrich Rudolf Hertz, long famous for his 1888 discovery of long-wavelength electromagnetic waves. Hertz delivered this address on 20 April 1885 as his inaugural lecture to the faculty at the Technische Hochschule in Karlsruhe (now the Universität Karlsruhe), where he was to make his most important contributions to physics. Although written over 110 years ago, this historical document records both Hertz’s insightful view of the Earth’s energy situation at that time and his remarkably good order-of-magnitude estimates of the energy sources then known to be available to the Earth.
Sliding temperatures of ice skates
Authors: Colbeck S. C. , Najarian L. , Smith H. B.
Published: March 2005

The two theories developed to explain the low friction of ice, pressure melting and frictional heating, require opposite temperature shifts at the ice-skate interface. The arguments against pressure melting are strong, but only theoretical. A set of direct temperature measurements shows that frictional heating is the dominant mechanism because temperature behaves in the manner predicted by the theory of frictional heating. Like snow skis, ice skates are warmed by sliding and then cool when the sliding stops. The temperature increases with speed and with thermal insulation. The sliding leaves a warm track on the ice surface behind the skate and the skate sprays warm ejecta.
Hidden mechanical momentum and the field momentum in stationary electromagnetic and gravitational systems
Authors: Hnizdo V.
Published: March 2005

The existence of hidden momentum, i.e., the mechanical momentum of a body the constituents of which move in a stationary manner but the center of mass of which is at rest in an external static field of force, is shown to follow from the general requirements of relativistic mechanics of continuous media, independently of whether the external forces are electromagnetic or gravitational. The hidden mechanical momentum is compensated by the momentum of the static fields in the system, necessitating, in the gravitational case, the existence of a gravinetic quasistatic gravitational field, which, in analogy to the magnetostatic field, is generated by a quasistationary current of mass and acts on a moving mass.
High efficiency diffractive lenses: Deduction of kinoform profile
Authors: Moreno Vicente , Román Juan Félix , Salgueiro José Ramón
Published: March 2005

The zone plates (diffractive lenses) are not commonly used as image formation systems owing to their low efficiency and multifocal characteristics. In this paper we make a revision of the Fresnel zone plate principles, and present various kinds of zone plates designed to solve the problem of obtaining a limited number of foci with higher efficiency. The purpose of this work was to design, by using Fermat’s principle, a zone-plate profile with high focusing efficiency in only one or two foci, while maintaining a low efficiency in the others. Applying Fermat’s principle to this task results in the kinoform profile of the plate. Calculation of the kinoform profile efficiency reveals that it is the best possible solution to this problem.
Nonlinear dynamical models and jerky motion
Authors: Linz Stefan J.
Published: March 2005

We investigate the connection between one-dimensional Newtonian jerky dynamics and nonlinear dynamical systems in a three-dimensional phase space. With exact transformations, we show that the Rössler model, as well as the Lorenz model, can be interpreted as jerky motion and discuss whether they are Newtonian or not. Moreover, Sprott’s model R is identified as one of the simplest Newtonian jerky dynamics that can lead to chaos. Using a wide class of jerk functions, we derive a criterion for being Newtonian jerky.
The human discharge chain
Authors: Dudley Scott C. , Heerema Bret D. , Haaland Ryan K.
Published: March 2005

The common classroom demonstration of a human chain, charged by a Van de Graaff generator, and then discharged via the person at the end of the chain touching ground, is analyzed as a capacitor and resistor circuit model. The energy deposited in each person in the chain is determined. Further, the effect of increasing energy deposited in the person who touched ground, as the number of people in the chain is increased, is shown and quantified.
Interference, diffraction, and refraction, via Dirac’s notation
Authors: Duarte F. J.
Published: March 2005

The diffraction grating equation and the law of refraction are derived, in the macroscopic domain, using a generalized interference equation derived via the application of Dirac’s notation to classical optics.
Angles—Let’s treat them squarely
Authors: Brownstein K. R.
Published: March 2005

We suggest a self-consistent treatment of the dimensions and units of the geometric quantity “angle.” The method regards “angle” as a fundamental dimensional physical quantity, on a par with length, mass, time, etc. All units (whether angular or otherwise) are treated on an equal footing and balance out correctly; in particular, “radian” units need never be spuriously inserted or deleted. The method could find application in algebraic and calculus symbolic manipulation computer programs to correctly process units of physical quantities. The technique necessitates a minor modification of the relation “s=Rθ” and its consequences, rather than any modification of the units of other physical quantities (such as moment arms) as previously suggested by others. We make several important clarifying distinctions: (a) ω [SI: rad⋅s−1] for rotational motion (as in θ=ωt) versus Ω [SI: s−1] for simple harmonic motion [as in x=xm cos(Ωt)], (b) geometric trigonometric functions whose arguments are angles [SI: rad] versus mathematical trigonometric functions whose arguments are pure numbers, (c) simple harmonic motion versus uniform circular motion in the reference circle analogy.
Overcoming naïve mental models in explaining the Doppler shift: An illusion creates confusion
Authors: Neuhoff John G. , McBeath Michael K.
Published: March 2005

A perceptual auditory illusion is described that may contribute to students’ misunderstanding of the physical principles of the Doppler shift. The illusion advances the formation of naïve mental models about the change in observed frequency that occurs as a sound source passes a stationary observer. Factors that may cause misunderstanding are addressed including the following: (i) the semantic distinctions between physical “frequency” and perceptual “pitch,” (ii) the influence of dynamic loudness on pitch, and (iii) the ambiguity of the word “rise” in describing the wave mechanics of the Doppler shift. Implications for teaching the principles of the Doppler shift include addressing the origin of naïve beliefs and using the illusion as a salient and conspicuous example of a breakdown of the correspondence between physics and perception.
The Wigner angle as an anholonomy in rapidity space
Authors: Aravind P. K.
Published: March 2005

A product of two non-collinear boosts (i.e., pure Lorentz transformations) can be written as the product of a boost and a rotation, the angle of rotation being known as Wigner’s angle. This paper demonstrates how the Wigner angle and final boost parameters can be calculated simply in terms of the initial boost parameters using hyperbolic trigonometry. It also demonstrates that the Wigner angle is the (negative) area of a rapidity triangle composed of the two non-collinear boosts and their resultant.
A modular, reconfigurable-cavity, pulsed dye laser for the advanced undergraduate laboratory
Authors: Sohl John E. , Payton Stephen G.
Published: March 2005

The modular pulsed dye laser described is extremely easy to build, is quickly reconfigurable into different laser cavity designs, and is usable for experiments in spectroscopy. The laser can be constructed with readily available optical components and simple hand tools. This laser is designed primarily to illustrate the performance differences of three different dye laser cavity designs: the Littrow grating (Hänsch) cavity, and both the single- and double-grating grazing incidence cavities. In the double-grating configuration, the laser’s linewidth of 0.007 nm is on the order of ten times narrower than many commercially available pulsed dye lasers. Thus the laser also has excellent performance as a spectroscopic tool. Construction, typical performance, and application details are described.
Metastable states in classical and quantum systems
Authors: Makela Mark , Parmley Samantha , Yu Roger
Published: March 2005

The classical vibrational metastable states in a one-dimensional two-mass system are investigated experimentally and theoretically via the transmission of a coherent wave packet propagating through the system. The Fourier transform of the vibrational signal recorded in between the masses reveals resonant excitations by the coherent wave packet. The time-resolved spectrum indicates that the lifetime of a metastable state of higher frequency is longer than that of lower frequency, which is in contrast with the quantum mechanical double-barrier system. This study, which is easily accessible to physics majors, also demonstrates quantum resonant tunneling in a very simple classical way.
Changing approach to teaching electromagnetism in a conceptually oriented introductory physics course
Authors: Galili Igal , Kaplan Dov
Published: March 2005

An approach emphasizing the complementarity of electric and magnetic fields within a weak relativistic approximation is suggested as a basis for presenting electromagnetism in an introductory university physics course. Within the electromagnetic unification approach, “magnetic force” and “electromagnetic induction” are each taught in a manner consistent with mechanics from a qualitative relativistic point of view. The Lorentz force and the magnetic flux rule are treated similarly, linking electrical and magnetic phenomena and improving the integrity and self-consistency of the course. The status of Faraday’s integral law is discussed and is shown to be of limited validity in this context.
New Practical Physics
Authors: Purcell Edward M.
Published: March 2005

In ways no one predicted physics in our time has been astonishingly useful and continually surprising. Has our teaching kept up? Some thoughts about tools and ideas from physics for the college student who wants to be some kind of scientist. [Reprinted from AAPT Pathways (Proceedings of the Fiftieth Anniversary Symposium of the AAPT), edited by Melba Phillips (American Association of Physics Teachers, Stony Brook, New York, 1981)]
Computer simulation of p–n junction devices
Authors: Sanjay Rebello N. , Ravipati Chandramouli , Zollman Dean A. , Escalada Lawrence T.
Published: March 2005

We present here a computer program—the Semiconductor Device Simulator—which simulates the working of three p–n junction devices: the light-emitting diode, the solar cell, and the tunnel diode. This program enables students to create the device starting with two pieces of intrinsic semiconductor material, and doping them appropriately to create a p–n junction device of their choice. While creating the device, students can observe the changes in the energy bands and Fermi level as a response to doping. The device, once created, can then be incorporated into a circuit where the students can observe the energy bands, the I–V graph, as well as the intensity spectrum of the device in response to the changes in applied voltage and/or incident light. No prior knowledge of higher level mathematics is required to use the program. The program is available for Windows™ and Macintosh™ platforms. The flexibility of the program allows it to be used by students over a range of academic levels. We have field tested the program along with associated materials in both high school and university environments. The current version of the program contains modifications based on these field tests.
The search for elementary particles with fractional electric charge and the philosophy of speculative experiments
Authors: Perl Martin L. , Lee Eric R.
Published: March 2005

All known elementary particles that can be isolated as individual particles have an electric charge that is equal in magnitude to the electron’s charge, q=1.6×10−19 C, or is zero. This includes the muon and tau charged leptons, the neutrinos, the photon, the nucleons, and the mesons. There have been many searches without confirmed success for isolated particles with fractional electric charge such as ±q/3, or ±q/2, or ±3q/2. The theory of the physics of elementary particles does not require the existence of such particles. In particular, current theory holds that quarks, whose charge is ±(1/3)q or ±2/3q, cannot be isolated. Despite past failures and current theory, we have been engaged for the past few years in a new search for isolated elementary particles with fractional electric charge. In the course of this paper we discuss models for fractional charge particles, summarize previous searches, and describe our experimental method; and because this is speculative research we will also present our thoughts on speculative experiments.
From problem solving to a knowledge structure: An example from the domain of electromagnetism
Authors: Bagno Esther , Eylon Bat-Sheva
Published: March 2005

An investigation of students’ knowledge after a traditional advanced high-school course in electromagnetism shows deficiencies of their knowledge in three major areas: (1) the structure of knowledge—e.g., realizing the importance of central ideas, such as Maxwell’s equations (expressed qualitatively); (2) conceptual understanding—e.g., understanding the relationships between the electric field and its sources; and (3) application of central relationships in problem solving. To remedy these deficiencies we propose an instructional model which integrates problem solving, conceptual understanding and the construction of the knowledge structure. The central activity of the students is a gradual construction of a hierarchical concept map organized around Maxwell’s equations as central ideas of the domain. The students construct the map in five stages: (1) SOLVE—they solve a set of problems that highlight the central ideas in the domain; (2) REFLECT—they reflect on the conceptual basis of their solutions; (3) CONCEPTUALIZE—they perform activities that deal with relevant conceptual difficulties; (4) APPLY—they carry out complex applications; (5) LINK—they link their activities to the evolving concept map. This integrative model (experimental treatment) was compared to an isolated treatment of drill and practice or treatment of conceptual difficulties without linkage to the proposed knowledge structure. The comparison shows that students in the experimental treatment performed better than the other students on measures of recall, conceptual knowledge and problem solving. Students in the experimental treatment were also able to transfer and extract central ideas in a domain different than physics.
Probing stereotypes through students’ drawings of scientists
Authors: Rahm Jrène , Charbonneau Paul
Published: March 2005

The Draw-A-Scientist Test is an assessment tool devised to explore and measure children’s stereotypical views of scientists. We administered this test to a group of 49 undergraduate and postgraduate students enrolled in a teacher certification program. While this was originally intended as a purely pedagogical exercise, we were struck by the degree to which the drawings so produced resembled, in stereotypical content, those usually produced by children. This suggests that stereotypes of science and scientists formed during childhood, presumably via the influence of the media, remain largely unaffected by the subsequent passage through high school and college, despite the fact that numerous real-life figures of science teachers and scientists are presumably encountered throughout those formative years. We argue that this state of affairs has subtle and far reaching consequences, and is worthy of our collective attention.
The young Huygens solves the problem of elastic collisions
Authors: Erlichson Herman
Published: March 2005

Christiaan Huygens was probably the first person to solve the problem of elastic collisions. He did this in the 1650s when he was only in his early twenties. The first formal publication of his general rule for the outcome of a head-on hard collision was in March 1669 in the Journal des Sçavans. Our present paper describes in detail Huygens’ work on elastic collisions. We focus particularly on how Huygens’ instinct for symmetry led him to a solution in the center-of-gravity reference frame. He readily transformed this solution to other frames using what we now call the Galilean velocity transformation. Huygens’ symmetry approach is quite different from the modern description of collisions using Newtonian action and reaction forces.
Classical antiparticles
Authors: Costella John P. , McKellar Bruce H. J. , Rawlinson Andrew A.
Published: March 2005

We review how antiparticles may be introduced in classical relativistic mechanics, and emphasize that many of their paradoxical properties can be more transparently understood in the classical than in the quantum domain.
Equilibrium charge density on a conducting needle
Authors: Andrews Mark
Published: March 2005

The concept of an equilibrium continuous charge density on a conducting line, although in some ways unphysical, does provide useful physical insight into needlelike conductors. It is shown that the charge density on such a line must be uniform. A simple method is developed for calculating the charge density on long, thin conductors with circular cross section. Also, the equilibrium distribution of N equal charges on a line is shown to approach equal spacing (except near the ends) as the number of charges grows.
Magnetic braking revisited
Authors: Aguirregabiria J. M. , Hernández A. , Rivas M.
Published: March 2005

The braking force acting on a conducting disk rotating under the influence of an external magnetic field of axial symmetry is calculated in a quasi-static approximation and the role played by the charge distributions induced in the disk is shown. The two cases of infinite and finite radius are considered to analyze the influence of edge effects and we obtain a general expression for the braking torque when the magnetic field has axial symmetry. The particular case of a uniform external magnetic field is used to show the working of a simplified model of a cylindrical battery. Analytical results are compared with those obtained by other authors.
Experimenting with magnetism: Ways of learning of Joann and Faraday
Authors: Cavicchi Elizabeth
Published: March 2005

This paper narrates learning as it evolved through experimental work and interpretation in two distinct investigations: the explorations of permanent magnets and needles conducted by a student, Joann, as I interactively interviewed her, and Faraday’s initial experimenting with diamagnetism, as documented in his Diary. Both investigators puzzled over details, revisited their confusions resiliently, and invented analogies as ways of extending their questioning; “misconceptions” and conflict were not explicit to their process. Additionally, Faraday formed interpretations—and doubts critiquing them—that drew upon his extensive experience with magnetism’s spatial behaviors. These two cases suggest that physics instruction could include opportunities for students’ development of their own investigatory learning.
Electric polarizability of a relativistic particle
Authors: Maize M. A. , Paulson S. , D’Avanti A.
Published: March 2005

A simple potential model is used to study the contribution of negative energy states to the static electric polarizability of a relativistic particle which is bound by a one-dimensional delta potential. The potential includes both Lorentz scalar and vector components. Contrary to the result based on nonrelativistic physics, we find it possible that the electric polarizability can have a negative sign.
Magnets at the corners of polygons
Authors: Stump Daniel R. , Pollack Gerald L. , Borysowicz Jerzy
Published: March 2005

We consider the statics and dynamics of N identical magnetic dipoles, with inertia, pinned at the corners of a regular polygon with N sides. We show that at equilibrium all dipoles are aligned tangent to the circumscribed circle. We find the normal modes and frequencies for oscillations about equilibrium, and discuss the dispersion relation. In the highest frequency normal mode the dipoles oscillate in phase with equal amplitudes, so no magnetic dipole radiation is emitted. In the limit N→∞, the equilibrium energy and the frequency of the symmetric mode are both related to ζ(3), where ζ is the Riemann zeta function.
A heuristic way of obtaining the Kerr metric
Authors: Enderlein Jörg
Published: March 2005

An intuitive, straightforward way of finding the metric of a rotating black hole is presented, based on the algebra of differential forms. The representation obtained for the metric displays a simplicity which is not obvious in the usual Boyer–Lindquist coordinates.
Making a pitch for the center of mass and the moment of inertia
Authors: Mei W. N. , Wilkins Dan
Published: March 2005

We propose some simple experiments to measure moments of inertia of certain physical pendula having high and low symmetry. Periods of oscillation, mass, and distance of the pivot from the center of mass are used to measure ICM for: (a) the “floating eagle,” an intriguing toy, and (b) a rectangular plate. Values of ICM obtained from measurements about different parallel axes may be checked for consistency.
Unified mean-field study of ferro- and antiferromagnetic behavior of the Ising model with external field
Authors: Vives Eduard , Castán Teresa , Planes Antoni
Published: March 2005

A simultaneous mean-field treatment, of both phenomena, ferro- and antiferromagnetism, in the framework of the Bragg–Williams theory, shows the importance of the interplay between the two corresponding order parameters in determining the features of the phase diagram. The problems of phase separation and order–disorder transition in binary alloys are also included in the solution. The different projections of the phase diagram are discussed.
The magnetic field of a current carrying cosmic string
Authors: Muriano A. G. R. , da Silva M. F. A.
Published: March 2005

The magnetostatic field of an infinite rectilinear current placed in the stationary gravitational field of a rotating cosmic string is found. An interesting aspect of this problem is that although the metric is mathematically very simple, its physical meaning is not trivial. It depends only on topological parameters. So, the cosmic string vacuum space–time is locally equivalent to the Minkowski space–time, but not globally. The calculations are so simple that they can easily be shown in the classroom.
What every musician knows about viscoelastic behavior
Authors: Vilela P. M. , Moscoso R. A. , Thompson D.
Published: March 2005

Every stringed instrument player knows that new nylon strings rapidly go out of tune, whereas metal strings do not. This is because metal strings show elastic behavior while nylon is viscoelastic. We present an experiment suitable for the undergraduate laboratory in which we measure the stress relaxation in a nylon string by monitoring the frequency of the note produced and show that it can be adequately described in terms of a model using Maxwell elements in series.
Quantum superpositions and Schrödinger cat states in quantum optics
Authors: Gerry C. C. , Knight P. L.
Published: March 2005

We describe the properties of a quantum system prepared in superpositions of classically distinguishable states. These states, often called Schrödinger cat states, are of great interest at present. We discuss how they may be realized in quantum optics using nonlinear interactions and cavity quantum electrodynamics. We first describe the quantum properties of field states in a cavity, and demonstrate the interference properties which characterize superposition states and discuss how fragile they are in dissipative environments. Finally, we review current experimental approaches which may realize these states.
Zero time dilation in an accelerating rocket
Authors: Gruber Ronald P. , Price Richard H.
Published: March 2005

We give a variation of the twin paradox of special relativity in which the relationship of acceleration of the rocket twin and time dilation is clarified.
Conceptual astronomy: A novel model for teaching postsecondary science courses
Authors: Zeilik Michael , Schau Candace , Mattern Nancy , Hall Shannon , Teague Kathleen W. , Bisard Walter
Published: March 2005

An innovative, conceptually based instructional model for teaching large undergraduate astronomy courses was designed, implemented, and evaluated in the Fall 1995 semester. This model was based on cognitive and educational theories of knowledge and, we believe, is applicable to other large postsecondary science courses. Major components were: (a) identification of the basic important concepts and their interrelationships that are necessary for connected understanding of astronomy in novice students; (b) use of these concepts and their interrelationships throughout the design, implementation, and evaluation stages of the model; (c) identification of students’ prior knowledge and misconceptions; and (d) implementation of varied instructional strategies targeted toward encouraging conceptual understanding in students (i.e., instructional concept maps, cooperative small group work, homework assignments stressing concept application, and a conceptually based student assessment system). Evaluation included the development and use of three measures of conceptual understanding and one of attitudes toward studying astronomy. Over the semester, students showed very large increases in their understanding as assessed by a conceptually based multiple-choice measure of misconceptions, a select-and-fill-in concept map measure, and a relatedness-ratings measure. Attitudes, which were slightly positive before the course, changed slightly in a less favorable direction.
Simple setup for detecting interference fringes produced by independent lasers
Authors: Basano Lorenzo , Chittofrati Roberto , Crivello Stefano , Piano Emanuele , Pontiggia Carlo
Published: March 2005

The visualization of interference fringes produced by the superposition of two different laser beams requires complex and costly demonstrations. This paper describes an experimental setup which (with the exclusion of an inexpensive and easy-to-build pair of optical guides) uses conventional laboratory equipment to detect the presence of the fringes.
Misconceptions about astronomical magnitudes
Authors: Schulman Eric , Cox Caroline V.
Published: March 2005

The present system of astronomical magnitudes was created as an inverse scale by Claudius Ptolemy in about 140 A.D. and was defined to be logarithmic in 1856 by Norman Pogson, who believed that human eyes respond logarithmically to the intensity of light. Although scientists have known for some time that the response is instead a power law, astronomers continue to use the Pogson magnitude scale. The peculiarities of this system make it easy for students to develop numerous misconceptions about how and why to use magnitudes. We present a useful exercise in the use of magnitudes to derive a cosmologically interesting quantity (the mass-to-light ratio for spiral galaxies), with potential pitfalls pointed out and explained.
The dynamics of a charged sphere and the electron
Authors: Rohrlich F.
Published: March 2005

A brief review of the history of the classical equations of motion of charged particles is given leading up to the present time. Emphasis is placed on the important role of the validity limits of the theory. The little known relativistic equations of motion of a surface-charged sphere are presented. Their proof and validity limits are discussed. An appendix gives the history and eventual solution of the stability problem (the “4/3 problem”). The emphasis is on understanding rather than on technical details.
Preparing physics majors for secondary-level teaching: The education concentration in the Haverford College physics program
Authors: Roelofs Lyle D.
Published: March 2005

It is easy to document both the strong demand for physics teachers at the secondary level and the fact that not all individuals currently in those positions are well qualified. Many undergraduate physics majors who might otherwise be interested do not pursue careers in teaching high school physics because the requirements for certification are quite strenuous in many states. We have accordingly developed at Haverford College a concentration in education for physics majors which provides experiential preparation for teaching physics but requires fewer courses beyond the standard physics major than does the typical curriculum leading to certification. We describe this concentration, the two key courses on which it is based, the career options it affords the B.S. physics major, and the experience of our recent graduates entering the high school teaching profession.
Interaction of circling relativistic charges and interference in their radiation
Authors: Gordeyev A. N.
Published: March 2005

The radiation emitted by two charges circling at opposite ends of a diameter at arbitrary uniform speed is considered, with special attention being paid to interference effects. The difference in the rate of radiation from the system and the sum of the powers emitted separately by each circling charge is shown to be equal to the work done by the particles on each other through their exact Liénard–Wiechert fields, in accordance with the Poynting theorem. Some peculiarities of the radiation at high and low speeds are noted and explained.
The not-so-simple harmonic oscillator
Authors: Peters Randall D. , Pritchett Tim
Published: March 2005

A model inspired by the behavior of a simple harmonic oscillator subject to dry sliding friction is applied to the damping of a variety of mechanical oscillators. In contrast to the conventional model of damping in mechanical systems, the new model predicts a logarithmic decrement of the motion which is quadratic in the period. This prediction agrees well with the observed period dependence of the long-period physical pendulum which was the primary focus of this investigation.
The relation between expressions for time-dependent electromagnetic fields given by Jefimenko and by Panofsky and Phillips
Authors: McDonald Kirk T.
Published: March 2005

The expressions of Jefimenko, which have received much recent attention in this Journal, are contained in Sec. 14.3 of the book Classical Electricity and Magnetism by Panofsky and Phillips. The latter develop these expressions further into a form that gives greater emphasis to the radiation fields. This article presents a derivation of the various expressions and discusses an apparent paradox in applying Panofsky and Phillips’s result to static situations.
Radiation from a superluminal source
Authors: McDonald Kirk T.
Published: March 2005

The sweep speed of an electron beam across the face of an oscilloscope can exceed the velocity of light, although, of course, the velocity of the electrons does not. Associated with this possibility, there should be a kind of Čerenkov radiation, as if the oscilloscope trace were due to a charge moving with superluminal velocity.
Electromagnetics in retarded time and photon localization
Authors: Mosley Shaun N.
Published: March 2005

Maxwell’s equations are presented in retarded time coordinates, source-free solutions are found which are instantaneously localized. The modified Lorentz force law is discussed.
Thermodynamic paths to Jensen’s inequality
Authors: Plastino A. R. , Plastino A. , Miller H. G.
Published: March 2005

Jensen’s inequality is obtained from thermodynamic arguments applied to two physical processes: temperature equalization in a set of N bodies, and height equalization of an incompressible fluid in a system of connected standpipes.
An analytically solvable model of dissipation
Authors: Fano U.
Published: March 2005

The initial energy of a pendulum weakly coupled to a stretched string of infinite length dissipates into waves traveling away along the string. The frequency spectrum of this process emerges from a simple algebraic procedure resting on its key features. Confining the string to a long but finite length revives the pendular motion periodically. This model illustrates basic aspects of dissipation, providing material for exercises on physicomathematical techniques.
Some properties of cycloid trajectories
Authors: Bruce Ian
Published: March 2005

The electric and magnetic forces acting on an ion in uniform crossed fields are shown to add to give a centripetal force of constant magnitude, moving with the ion in a cycloid trajectory. A comparison is made with the analogous forces in the classical brachistrochrone case of a bead sliding down a frictionless cycloid-shaped wire.
A simple calculation of the deflection of light in a Schwarzschild gravitational field
Authors: Lerner L.
Published: March 2005

The problem of the deflection of light in a medium with varying refractive index is applied to the motion of light in a weak Schwarzschild gravitational field. In contrast to the standard deviation, the present method is physically transparent, providing a clear reason for the factor-of-2 deviation of the general relativistic result from that of the Newtonian theory without any detailed calculation.
Bell and Greenberger, Horne, and Zeilinger theorems revisited
Authors: Ryff Luiz Carlos
Published: March 2005

The original theorems of Bell and of Greenberger, Horne, and Zeilinger (GHZ) are extended from ideal to real situations using an intuitive and straightforward approach. This alternative derivation has the merit of showing that if a theorem is valid whenever we have perfect correlations, it cannot be totally wrong in the case of almost perfect correlations. Therefore, it is probably easy (i.e., by introducing only small changes in the original argument) to extend the result to deal with imperfect correlations.
Quantum Hamilton–Jacobi formalism and the bound state spectra
Authors: Bhalla R. S. , Kapoor A. K. , Panigrahi P. K.
Published: March 2005

It is well known in classical mechanics that the frequencies of a periodic system can be obtained rather easily through the action variable, without completely solving the equation of motion. Analogously, the equivalent quantum action variable appearing in the quantum Hamilton–Jacobi formalism can provide the energy eigenvalues of a bound state problem, without the necessity of solving the corresponding Schrödinger equation explicitly. This elegant and useful method is elucidated here in the context of some known and not so well-known solvable potentials. It is also shown how this method provides an understanding as to why approximate quantization schemes such as ordinary and supersymmetric WKB can give exact answers for certain potentials.
Experimental measurements on a simulated lumped transmission line
Authors: Smith H. J. T. , Blackburn James A.
Published: March 2005

A novel design for simulating a lumped element transmission line is described. Op-amp subcircuits replace discrete inductances—an approach which overcomes a number of disadvantages associated with conventional components. The apparatus models a lossy line which is free of amplitude and phase distortion. Experiments are described which demonstrate the design’s precise measurement capabilities with respect to determining frequency-dependent input impedance and phase shift, as well as the real and imaginary parts of the complex propagation function. Several pulse experiments are also discussed.
Hidden momentum and the electromagnetic mass of a charge and current carrying body
Authors: Hnizdo V.
Published: March 2005

The contribution of the electromagnetic self-field to the energy and momentum of a charge and/or current carrying body is considered within classical physics and discussed in simple terms using nontrivial exactly solvable examples. The Lorentz-transformation properties of the energy and momentum of the body can be maintained by taking into account the relativistic effects of the mechanical stresses due the sources of the self-field, or by separating the energy and momentum of a moving self-field from those of a nonelectromagnetic origin in a relativistically covariant way. In either procedure, a proper account must be taken of the hidden mechanical momentum that, in general, is contained in a stationary body that carries both charge and current, and which is equal and opposite to the momentum of the static electromagnetic self-field. Hidden momentum and the momentum of a static electromagnetic field are indispensable concepts of direct physical significance in classical electrodynamics.
Role of Marine Biology in Glacial-Interglacial CO
2
Cycles
Authors: Kohfeld Karen E. , Quéré Corinne Le , Harrison Sandy P. , Anderson Robert F.
Published: March 2005

It has been hypothesized that changes in the marine biological pump caused a major portion of the glacial reduction of atmospheric carbon dioxide by 80 to 100 parts per million through increased iron fertilization of marine plankton, increased ocean nutrient content or utilization, or shifts in dominant plankton types. We analyze sedimentary records of marine productivity at the peak and the middle of the last glacial cycle and show that neither changes in nutrient utilization in the Southern Ocean nor shifts in plankton dominance explain the CO
2
drawdown. Iron fertilization and associated mechanisms can be responsible for no more than half the observed drawdown.