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The Physics Teacher

American Journal of Physics»
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SECTION LISTING

AWARDS
PAPERS
APPARATUS AND DEMONSTRATION NOTES
PHYSICS EDUCATION RESEARCH SECTION
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Volume 70

Issue 12 | Dec 2002 | pp. 1175-1275

Issue 11 | Nov 2002 | pp. 1081-1167

Issue 10 | Oct 2002 | pp. 983-1071

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Dec 2002

Volume 70, Issue 12, pp. 1175-1275

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AWARDS

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The 2001 Paul Klopsteg Memorial Lecture: Cosmology: Man’s place in the universe (a deconstruction)

Virginia Trimble

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1175

Online Publication Date: Nov 2002

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The history of the universe makes a reasonably coherent story, beginning with a hot, dense phase (the Big Bang), continuing with the formation and evolution of galaxies, stars, and planets, and reaching by now the appearance of life and intelligence (suitably defined). Some parts of the story, for instance, the evolution of stars, are well understood. Others are only fuzzy outlines (the formation of galaxies and the beginnings of life). All are heavily dependent upon the universe having key characteristics very close to the actual ones. These include the four forces of physics and about four cosmological parameters. CMPitU is a talk that tries to tell this story. The deconstruction addressed how much confidence we can place in the various chapters and variants in narrative technique. © 2002 American Association of Physics Teachers.

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01.50.-i	Educational aids
98.80.-k	Cosmology

PAPERS

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Thin lens ray tracing

Ian R. Gatland

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1184 | Cited 4 times

Online Publication Date: Nov 2002

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A ray tracing approach to thin lens analysis, based on a vector form of Snell’s law for paraxial rays, is proposed as an alternative to the usual approach in introductory physics courses. The ray tracing approach accommodates skew rays and thus provides a complete analysis. © 2002 American Association of Physics Teachers.

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42.15.Dp	Wave fronts and ray tracing
01.40.Di	Course design and evaluation

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Transient behavior of simple RC circuits

Norris W. Preyer

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1187 | Cited 1 time

Online Publication Date: Nov 2002

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I report on simulations of the evolution of surface charges, the retarded electric potential, and the electric field in a simple resistor–capacitor (RC) circuit and in an RC circuit with a switch. The circuits have high resistance, so radiation and inductive effects are not significant. The simulations illustrate nonquasistatic effects due to the finite speed of light, and should be useful in teaching students how circuits respond to changes. © 2002 American Association of Physics Teachers.

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01.50.-i	Educational aids
84.30.Bv	Circuit theory

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Energy balance problems in systems of induced and permanent electric and magnetic dipoles

Robert A. Anderson and James E. Martin

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1194 | Cited 2 times

Online Publication Date: Nov 2002

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There are many problems where a detailed understanding of the interaction energy of systems of dipoles is needed, including electrorheological and magnetorheological fluids, ferrofluids, magnetic composites, and dielectrics. We have constructed soluble microscopic problems involving electric and magnetic dipoles to investigate energy balance, and have come to some understanding of the proper form of the dipolar free energy in aggregations of induced or permanent dipoles and mixtures thereof. The resulting equations clarify misconceptions sometimes found in the literature, and lead to greater intuition about the subtle aspects of the dipolar interactions. We discuss the application of these equations to dipole simulations to extract the dipole energy and material dielectric constant. © 2002 American Association of Physics Teachers.

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41.20.Gz	Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
41.20.Cv	Electrostatics; Poisson and Laplace equations, boundary-value problems
75.50.Mm	Magnetic liquids
83.80.Gv	Electro- and magnetorheological fluids
75.50.Tt	Fine-particle systems; nanocrystalline materials

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Harmonic? Anharmonic? Inharmonic?

Neville H. Fletcher

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1205 | Cited 4 times

Online Publication Date: Nov 2002

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In molecular spectroscopy, an anharmonic oscillator has a nonparabolic potential which results in a nonharmonic absorption spectrum, but the same oscillator treated classically has a precisely harmonic vibrational spectrum. To avoid confusion, it is suggested that such an oscillator should simply be called nonlinear. The term “inharmonic” is suggested as an appropriate descriptor for classical oscillators, such as metal bars, that have nonharmonic vibrational spectra even in the linear limit of small vibrations. © 2002 American Association of Physics Teachers.

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45.05.+x

General theory of classical mechanics of discrete systems

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Experimental study of the Neumann and Dirichlet boundary conditions in two-dimensional electrostatic problems

Salvador Gil, Martín Eduardo Saleta, and Dina Tobia

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1208 | Cited 3 times

Online Publication Date: Nov 2002

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We present the results of an experimental study of the implications of the Neumann and Dirichlet boundary conditions on the solution of two-dimensional electrostatic problems. The experimental setup is simple and low cost. The experimental results are compared with theoretical expectations using a spreadsheet program to solve Laplace’s equation with the appropriate boundary conditions. Excellent agreement is found between the experimental results and the calculations. The simplicity of the experiment and of the theoretical interpretation makes this experiment accessible to beginning students. © 2002 American Association of Physics Teachers.

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01.50.ht	Instructional computer use
41.20.Cv	Electrostatics; Poisson and Laplace equations, boundary-value problems

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The vanishing of magnetic flux over a closed surface

Bekir Karaoglu

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1214

Online Publication Date: Nov 2002

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A simple proof of the vanishing of magnetic flux over a closed surface, based on elementary vector algebra and symmetry considerations, is presented. © 2002 American Association of Physics Teachers.

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03.50.De	Classical electromagnetism, Maxwell equations
01.40.-d	Education
41.20.-q	Applied classical electromagnetism
02.10.Ud	Linear algebra

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Relativistic causality and conservation of energy in classical electromagnetic theory

A. Kislev and L. Vaidman

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1216 | Cited 1 time

Online Publication Date: Nov 2002

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Causality puts certain constraints on the change of the electromagnetic field due to the change in motion of charged particles. Naive calculations of the electromagnetic energy and the work performed by the electromagnetic fields which take these constraints into account might lead to paradoxes involving the apparent nonconservation of energy. A few paradoxes of this type for the simple motion of two charges are presented and resolved in a quantitative way providing deeper insight into various relativistic effects in classical electromagnetic theory. © 2002 American Association of Physics Teachers.

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03.50.De	Classical electromagnetism, Maxwell equations
03.30.+p	Special relativity

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A noncalculus proof that Fermat’s principle of least time implies the law of refraction

Harald Helfgott and Michel Helfgott

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1224 | Cited 1 time

Online Publication Date: Nov 2002

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We provide an algebraic proof of the fact that Fermat’s principle of least time implies Snell’s law. This proof is closer to Fermat’s original approach than the usual calculus-based developments of the subject. © 2002 American Association of Physics Teachers.

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01.50.-i	Educational aids
42.25.Gy	Edge and boundary effects; reflection and refraction

APPARATUS AND DEMONSTRATION NOTES

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Studying collisions in the general physics laboratory with quadrature light emitting diode sensors

P. A. DeYoung and B. Mulder

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1226 | Cited 1 time

Online Publication Date: Nov 2002

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We have developed the means to measure position rapidly and precisely as a function of time in the general physics laboratory. These measurements are of sufficient quality that velocities and accelerations can be calculated from the position data using numerical derivatives. The precision of the measurements is such that any disagreement between theoretical expectations and experimental measurements is less than a few percent. Measurements of the system under study can be made as rapidly as every 200 μs, which is faster than the typical time scales over which the system changes. Measuring rapidly also allows one to investigate additional phenomena not previously accessible and to see features of the physics previously unobserved. The measurement system is based on commercially available sensors, computer hardware, and computer software (LABVIEW™). Many general physics laboratories based on this system have been developed but only an investigation of Newton’s second law will be described here. © 2002 American Association of Physics Teachers.

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01.50.Pa	Laboratory experiments and apparatus
45.50.Tn	Collisions
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

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Tabletop thermoacoustic refrigerator for demonstrations

Daniel A. Russell and Pontus Weibull

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1231

Online Publication Date: Nov 2002

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An inexpensive (less than $25) tabletop thermoacoustic refrigerator for demonstration purposes was built from a boxed loudspeaker, acrylic tubing and sheet, a roll of 35 mm film, fishing line, an aluminum plug, and two homemade thermocouples. Temperature differences of more than 15 °C were achieved after running the cooler for several minutes. While nowhere near the efficiency of devices described in the literature, this demonstration model effectively illustrates the behavior of a thermoacoustic refrigerator. © 2002 American Association of Physics Teachers.

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01.50.My	Demonstration experiments and apparatus
07.20.Mc	Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
43.35.Ud	Thermoacoustics, high temperature acoustics, photoacoustic effect

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A simple instrument for measuring time intervals with subnanosecond resolution

F. Fontanelli, L. Repetto, and R. Chittofrati

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1234

Online Publication Date: Nov 2002

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We have built a simple and inexpensive instrument capable of measuring time intervals from 0 up to 100 ns with a 0.1-ns resolution. We use easy-to-find components, and the construction can be performed by an undergraduate student. © 2002 American Association of Physics Teachers.

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01.50.Pa	Laboratory experiments and apparatus
06.30.Ft	Time and frequency

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A simple method for measuring atmospheric pressure

S. Velasco, A. González, F. L. Román, and J. A. White

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1236 | Cited 1 time

Online Publication Date: Nov 2002

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A simple and low-cost experimental method for measuring atmospheric pressure is proposed. A 100 ml glass syringe is used. The only theoretical requirement is Boyle’s law for ideal gases. © 2002 American Association of Physics Teachers.

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01.50.Pa	Laboratory experiments and apparatus
93.85.-q	Instruments and techniques for geophysical research: Exploration geophysics

PHYSICS EDUCATION RESEARCH SECTION

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The challenge of changing deeply held student beliefs about the relativity of simultaneity

Rachel E. Scherr, Peter S. Shaffer, and Stamatis Vokos

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1238 | Cited 19 times

Online Publication Date: Nov 2002

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Previous research indicates that after standard instruction, students at all levels often construct a conceptual framework in which the ideas of absolute simultaneity and the relativity of simultaneity co-exist. We describe the development and assessment of instructional materials intended to improve student understanding of the concept of time in special relativity, the relativity of simultaneity, and the role of observers in inertial reference frames. Results from pretests and post-tests are presented to demonstrate the effect of the curriculum in helping students deepen their understanding of these topics. Excerpts from taped interviews and classroom interactions help illustrate the intense cognitive conflict that students encounter as they are led to confront the incompatibility of their deeply held beliefs about simultaneity with the results of special relativity. © 2002 American Association of Physics Teachers.

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

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College physics students’ epistemological self-reflection and its relationship to conceptual learning

David B. May and Eugenia Etkina

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1249 | Cited 19 times

Online Publication Date: Nov 2002

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Students should develop self-reflection skills and appropriate views about knowledge and learning, both for their own sake and because these skills and views may be related to improvements in conceptual understanding. We explored the latter issue in the context of an introductory physics course for first-year engineering honors students. As part of the course, students submitted weekly reports, in which they reflected on how they learned specific physics content. The reports by 12 students were analyzed for the quality of reflection and some of the epistemological beliefs they exhibited. Students’ conceptual learning gains were measured with standard survey instruments. We found that students with high conceptual gains tend to show reflection on learning that is more articulate and epistemologically sophisticated than students with lower conceptual gains. Some implications for instruction are suggested. © 2002 American Association of Physics Teachers.

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01.40.G-

Curricula and evaluation

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The relationship between mathematics preparation and conceptual learning gains in physics: A possible “hidden variable” in diagnostic pretest scores

David E. Meltzer

American Journal of Physics -- December 2002 -- Volume 70, Issue 12, pp. 1259 | Cited 19 times

Online Publication Date: Nov 2002

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There have been many investigations into the factors that underlie variations in individual student performance in college physics courses. Numerous studies report a positive correlation between students’ mathematical skills and their exam grades in college physics. However, few studies have examined students’ learning gain resulting from physics instruction, particularly with regard to qualitative, conceptual understanding. We report on the results of our investigation into some of the factors, including mathematical skill, that might be associated with variations in students’ ability to achieve conceptual learning gains in a physics course that employs interactive-engagement methods. It was found that students’ normalized learning gains are not significantly correlated with their pretest scores on a physics concept test. In contrast, in three of the four sample populations studied it was found that there is a significant correlation between normalized learning gain and students’ preinstruction mathematics skill. In two of the samples, both males and females independently exhibited the correlation between learning gain and mathematics skill. These results suggest that students’ initial level of physics concept knowledge might be largely unrelated to their ability to make learning gains in an interactive-engagement course; students’ preinstruction algebra skills might be associated with their facility at acquiring physics conceptual knowledge in such a course; and between-class differences in normalized learning gain may reflect not only differences in instructional method, but student population differences (“hidden variables”) as well. © 2002 American Association of Physics Teachers.

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