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Nov 2008

Volume 76, Issue 11, pp. 989-1079

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THE SCANDAL OF QUANTUM MECHANICS

N. G. van Kampen

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 989 | Cited 5 times

Online Publication Date: Oct 2008

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Abstract Unavailable
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03.65.-w Quantum mechanics
01.70.+w Philosophy of science

FALLS FROM A HEIGHT

Jay M. Pasachoff

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 990

Online Publication Date: Oct 2008

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Abstract Unavailable
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47.00.00 Fluid dynamics
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Photorealistic visualization of imaging in canonical optical resonators

John Nelson, Johannes Courtial, and Graeme Whyte

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 991 | Cited 1 time

Online Publication Date: Oct 2008

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We investigate the capability of open source freeware ray tracing rendering software to demonstrate the imaging properties of canonical optical resonators. This software can directly visualize the imaging properties of canonical resonators. We can also demonstrate effects such as the trapping of light rays in geometrically stable resonators and the formation of fractal intensity patterns in the eigenmodes of geometrically unstable resonators.
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42.00.00 Optics

A periodic structure for electronic signals and demonstration of electronic lasing

Serge Doiron, Christophe Giller, Normand Beaudoin, and Alain Haché

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 996 | Cited 1 time

Online Publication Date: Oct 2008

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A sequence of electronic phase shifters and partial reflectors/transmitters is shown to form a true periodic scattering structure for electronic signals, complete with stop bands, interference, and dispersion effects. An experimental demonstration at 1 kHz is made with supporting theoretical results. As with conventional periodic media, sharp defect modes in the forbidden band arise when the periodicity is broken. When gain is added to the structure, a type of lasing action is observed that in almost every aspect is similar to conventional lasers.
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01.50.Pa Laboratory experiments and apparatus
42.00.00 Optics
84.30.-r Electronic circuits

Optical super-resolution with aperture-function engineering

E. Ramsay, K. A. Serrels, A. J. Waddie, M. R. Taghizadeh, and D. T. Reid

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1002

Online Publication Date: Oct 2008

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We demonstrate optical super-resolution (resolution better than conventional diffraction-limited resolution) in a simple optical configuration by using annular apertures to manipulate the pupil function of the system. The theoretical basis of the technique is described, and it is shown how good agreement between theory and experiment can be achieved by suitable selection of the principal system parameters. The ready implementation and suitability for theoretical interpretation makes the demonstration a good candidate for an undergraduate laboratory experiment in classical optics.
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42.00.00 Optics
01.50.Pa Laboratory experiments and apparatus

The classical dynamics of Rydberg Stark atoms in momentum space

J. Murray-Krezan

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1007 | Cited 1 time

Online Publication Date: Oct 2008

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The classical dynamics of a bound electron in a static electric field is discussed. The well-known Hamiltonian–Jacobi equations are examined and reexpressed in momentum coordinates, the preferred coordinates for the interpretation of many experimental measurements. It is shown that the combined Coulomb and static electric fields result in classically forbidden regions in momentum space. The equations of motion are discussed and the role of the electron’s angular momentum is described.
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30.00.00 ATOMIC AND MOLECULAR PHYSICS
47.00.00 Fluid dynamics

The angular momentum of photons in a circularly polarized beam

D. Kiang and K. Young

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1012 | Cited 1 time

Online Publication Date: Oct 2008

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We find the angular momentum of a photon in a circularly polarized beam by evaluating the energy and angular momentum imparted by a classical plane wave to a point charge for an arbitrary linear response. The only quantum ingredient used is the energy of a photon E=ℏω. Maxwell’s equations are not invoked beyond plane waves. Several previous results emerge as special cases of the derivation, which connects readily to experiments that measure the angular momentum of classical light.
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42.00.00 Optics

Influence of a humidor on the aerodynamics of baseballs

Edmund R. Meyer and John L. Bohn

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1015 | Cited 3 times

Online Publication Date: Oct 2008

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We investigate whether storing baseballs in a controlled humidity environment significantly affects their aerodynamic properties. We measure the change in diameter and weight of baseballs as a function of relative humidity in which the balls are stored. The trajectories of pitched and batted baseballs are modeled to assess the difference between those stored at 30% relative humidity versus 50% relative humidity. We find that a drier baseball will curve slightly more than a humidified one for a given pitch velocity and rotation rate. We also find that aerodynamics alone would add 2 ft to the distance a wetter baseball ball is hit. This increased distance is compensated by a 6 ft reduction in the batted distance due to the change in the coefficient of restitution of the ball. We discuss consequences of these results for baseball played at Coors Field in Denver, where baseballs have been stored in a humidor at 50% relative humidity since 2002.
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01.55.+b General physics
47.00.00 Fluid dynamics

Quantum noise detection: A portable and educational system

Jean-François Morizur, Massimiliano Colla, and Hans-A. Bachor

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1022

Online Publication Date: Oct 2008

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Quantum noise is a key feature of laser beams. It is both a limiting effect in contemporary optical measurements and a manifestation of the quantum nature of light. Its properties distinguish it from classical noise. We demonstrate a simple, reliable, and portable apparatus using low cost commercial lasers and electronics that provides evidence of these properties.
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01.50.Pa Laboratory experiments and apparatus

Time asymmetry in a dynamical model of the one-dimensional ideal gas

A. D. Boozer

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1026 | Cited 1 time

Online Publication Date: Oct 2008

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We present a simple dynamical model of the one-dimensional ideal gas and show how it can be used to introduce a number of fundamental ideas in statistical mechanics. We use the model to illustrate the role of initial conditions in explaining time asymmetry and show that although the dynamical model is time-reversal invariant, the macroscopic behavior of the gas can be time-asymmetric if the initial conditions are chosen properly.
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05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems

Entropy and evolution

Daniel F. Styer

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1031 | Cited 6 times

Online Publication Date: Oct 2008

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Quantitative estimates of the entropy involved in biological evolution demonstrate that there is no conflict between evolution and the second law of thermodynamics. The calculations are elementary and could be used to enliven the thermodynamics portion of a high school or introductory college physics course.
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05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems

Some insights from total collapse in the N-body problem

Sérgio B. Volchan

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1034

Online Publication Date: Oct 2008

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We discuss the Sundman–Weierstrass theorem of total collapse in its historical context. This remarkable and relatively simple result, a type of stability criterion, is at the crossroads of some interesting developments in the gravitational N-body problem. We use it as motivation to explore the connections to such important concepts as integrability, singularities, and typicality in order to gain insight into the transition from a predominantly quantitative to a novel qualitative approach to dynamical problems that took place at the end of the 19th century.
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47.00.00 Fluid dynamics

The square cat

E. Putterman and O. Raz

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1040

Online Publication Date: Oct 2008

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We present a simple two-dimensional model of a “cat”—a body with zero angular momentum that can rotate itself with no external forces. The model is used to explain the nature of a gauge theory and to illustrate the importance of noncommutative operators. We compare the free-space cat in Newtonian mechanics and the same problem in Aristotelian mechanics at low Reynolds numbers (with the velocity proportional to the force rather than to the acceleration). This example shows the analogy between (angular) momentum in Newtonian mechanics and (torque) force in Aristotelian mechanics. We discuss a topological invariant common to the model in free space and at low Reynolds number.
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47.00.00 Fluid dynamics

Energy and momentum in special relativity

Gregory S. Adkins

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1045 | Cited 2 times

Online Publication Date: Oct 2008

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The special relativistic expressions for momentum and energy are obtained by requiring their conservation in a totally inelastic variant of the Lewis–Tolman symmetric collision. The resulting analysis is simpler and more straightforward than the usual textbook treatments of relativistic dynamics.
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03.30.+p Special relativity

Electromagnetic field of a linear antenna

Norman Derby and Stanislaw Olbert

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1048 | Cited 1 time

Online Publication Date: Oct 2008

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Animated computer simulations of the electric field of a radiating antenna can capture the attention of students in introductory electromagnetism courses and stimulate active discussions. The simulations raise questions not usually addressed in textbooks. In certain cases, some of the field lines appear to move toward the antenna, the speed of the field lines can change as they move, and the field lines exhibit strange behavior (circling or splitting) at certain points. Because their fields can be expressed in terms of elementary functions, animations of point dipole antennas are common, but animations showing the fields of antennas with more realistic lengths are not as common because analytical expressions for these fields are not as well known. We show that it is possible to derive analytical expressions in terms of elementary functions for the electromagnetic field of linear antennas of finite length. We draw attention to an open-source method for displaying the fine details within the field patterns and then give a general discussion of singular points and their motions, derive expressions for their location and phase velocity, and apply these results to some of the phenomena that are visible in visualizations of the fields of various antennas.
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41.00.00 Electromagnetism; electron and ion optics
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Blogging in the physics classroom: A research-based approach to shaping students’ attitudes toward physics

Gintaras Duda and Katherine Garrett

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1054 | Cited 1 time

Online Publication Date: Oct 2008

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Although there has been much research on how to help students learn physics, students still come away without a deep understanding of how physics has transformed the world around them and almost all leave with decreased expectations and a more negative attitude toward physics. We discuss an experiment to address this problem: a course weblog which discusses real-world applications of physics and engages students in discussion and thinking outside of class. Students’ attitudes toward the value of physics and its applicability to the real-world were probed using a 26-question Likert scale survey over the course of four semesters in an introductory physics course. We found that students who did not participate in the blog generally exhibited a deterioration in attitude toward physics as seen previously. Students who read, commented, and were involved with the blog maintained their initially positive attitudes toward physics. Student response to the blog was overwhelmingly positive, with students claiming that the blog made the subjects studied in the classroom come alive for them and seem more relevant.
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01.40.Fk Research in physics education

Peer instruction: From Harvard to the two-year college

Nathaniel Lasry, Eric Mazur, and Jessica Watkins

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1066 | Cited 11 times

Online Publication Date: Oct 2008

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We compare the effectiveness of a first implementation of peer instruction (PI) in a two-year college with the first PI implementation at a top-tier four-year research institution. We show how effective PI is for students with less background knowledge and what the impact of PI methodology is on student attrition in the course. Results concerning the effectiveness of PI in the college setting replicate earlier findings: PI-taught students demonstrate better conceptual learning and similar problem-solving abilities than traditionally taught students. However, not previously reported are the following two findings: First, although students with more background knowledge benefit most from either type of instruction, PI students with less background knowledge gain as much as students with more background knowledge in traditional instruction. Second, PI methodology is found to decrease student attrition in introductory physics courses at both four-year and two-year institutions.
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01.40.Fk Research in physics education
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Putting things on the energy shell

George Csanak, L. A. Collins, and D. P. Kilcrease

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1070

Online Publication Date: Oct 2008

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Abstract Unavailable
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03.65.-w Quantum mechanics

A simple model for inelastic collisions

J. M. Aguirregabiria, A. Hernández, and M. Rivas

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1071

Online Publication Date: Oct 2008

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Abstract Unavailable
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47.00.00 Fluid dynamics
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Roughness effects on contact angle measurements

Bernard J. Ryan and Kristin M. Poduska

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1074 | Cited 3 times

Online Publication Date: Oct 2008

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We have developed a simple and economical procedure to demonstrate the effects of roughness and wetting fraction on the equilibrium contact angles of liquid droplets on solid surfaces. Contact angles for droplets placed on a rough surface, which wet only a portion of the surface, are larger than the contact angles of droplets formed by condensation of steam, which wet the surface more completely. These contact angle data facilitate assessments of changes in true surface area, due to surface roughening, as well as changes in the fractional contact areas of the water droplets, due to the formation of air pockets between the rough surface and the droplet.
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01.50.Pa Laboratory experiments and apparatus
60.00.00 CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
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Quantum Superposition: Counterintuitive Consequences of Coherence, Entanglement and Interference

Mark P. Silverman and Leslie E. Ballentine, Reviewer, Reviewer

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1078

Online Publication Date: Oct 2008

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Abstract Unavailable
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01.30.Vv Book reviews
03.65.-w Quantum mechanics

Erratum: “Review of A First Course in Scientific Computing: Symbolic, Graphic, and Numeric Modeling” [Am. J. Phys. 74 (7), 653–655 (2006)]

Rubin H. Landau and R. Torsten Clay, Reviewer, Reviewer

American Journal of Physics -- November 2008 -- Volume 76, Issue 11, pp. 1079

Online Publication Date: Oct 2008

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Abstract Unavailable
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01.30.Vv Book reviews
02.70.-c Computational techniques; simulations
99.10.-x Errata and other corrections
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