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Feb 2008

Volume 76, Issue 2, pp. 101-191

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COMPARING 9/11 TO 11/22

Jay M. Pasachoff

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 101 | Cited 3 times

Online Publication Date: Jan 2008

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Abstract Unavailable
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01.75.+m Science and society

CAUSAL EQUATIONS FOR ELECTRIC AND MAGNETIC FIELDS AND MAXWELL'S EQUATIONS: COMMENT ON A PAPER BY HERAS

O. D. Jefimenko

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 101 | Cited 3 times

Online Publication Date: Jan 2008

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Abstract Unavailable
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41.00.00 Electromagnetism; electron and ion optics

AUTHOR’S RESPONSE

José A. Heras

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 101 | Cited 2 times

Online Publication Date: Jan 2008

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41.00.00 Electromagnetism; electron and ion optics
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General relativity for sophomores

Edmund Bertschinger and Edwin F. Taylor

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 103 | Cited 1 time

Online Publication Date: Jan 2008

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Abstract Unavailable
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04.00.00 General relativity and gravitation
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Resource Letter Scy-3: Superconductivity

N. P. Butch, M. C. de Andrade, and M. B. Maple

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 106

Online Publication Date: Jan 2008

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This Resource Letter provides a guide to the literature on superconductivity. Since the last Resource Letter on superconductivity, Scy-2, was published in 1970, there have been dramatic advances in our basic understanding of superconductivity, discovery of new superconducting materials, and improved technological exploitation of superconductors. We review basic phenomenology, followed by concise descriptions of several main classes of superconductors recognized today. Journal articles and books are cited for the following topics: Conventional superconductors, paramagnetic impurities in superconductors, magnetically ordered superconductors, heavy fermion superconductors, high Tc superconductors, organic superconductors, applications of superconductivity, and laboratory demonstrations of superconductivity. Owing to the large volume of available literature on superconductivity, the journal articles and books we discuss constitute good starting points for further exploration of particular topics.
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01.30.Rr Surveys and tutorial papers; resource letters

The effect of spin on the flight of a baseball

Alan M. Nathan

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 119 | Cited 16 times

Online Publication Date: Jan 2008

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Measurements are presented of the Magnus force on a spinning baseball. The experiment utilizes a pitching machine to project the baseball horizontally, a high-speed motion analysis system to determine the initial velocity and angular velocity and to track the trajectory over 5 m of flight, and a ruler to measure the total distance traversed. Speeds in the range v=50–110 mph and spin rates ω (topspin or backspin) in the range 1500–4500 rpm were utilized, corresponding to Reynolds numbers of Re=(1.1–2.4)×105 and spin factors S≡Rω∕v in the range 0.090–0.595. Least-squares fits were used to extract the initial parameters of the trajectory and to determine the lift coefficients. Comparison is made with previous measurements and parametrizations, and implications for the effect of spin on the flight of a baseball are discussed. The lift coefficient CL is found not to depend strongly on v at fixed values of S.
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01.55.+b General physics

Coupled oscillations in suspended magnets

Michael J. Moloney

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 125 | Cited 1 time

Online Publication Date: Jan 2008

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A pair of strong magnets suspended by a single thread between them can act as a pendulum and also exhibit torsion as the magnets align with the Earth’s magnetic field. This arrangement demonstrates visible coupled oscillations, alternating between pendulum motion and twisting about the line of the thread, often at large angles. The vertical component of the Earth’s magnetic field is the coupling agent between the pendulum and twisting motions. The pendulum and torsion motions become uncoupled if an external coil is used to cancel this field component. An analysis of this motion is in agreement with experimental observations.
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47.00.00 Fluid dynamics

Measurement of mutual inductance from the frequency dependence of impedance of AC coupled circuits using a digital dual-phase lock-in amplifier

Michael J. Schauber, Seth A. Newman, Lindsey R. Goodman, Itsuko S. Suzuki, and Masatsugu Suzuki

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 129 | Cited 1 time

Online Publication Date: Jan 2008

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We present a simple method for determining the mutual inductance between two coils in a coupled AC circuit using a digital dual-phase lock-in amplifier. The frequency dependence of the real and imaginary parts is measured as the coupling is changed. The mutual inductance decreases as the distance d between the centers of coils is increased. We show that the coupling is proportional to d−n with n≈3. This coupling is similar to that of two magnetic dipoles.
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01.50.Pa Laboratory experiments and apparatus
84.00.00 Electronics; radiowave and microwave technology; direct energy conversion and storage

Revisiting the radiation from a suddenly moving sheet of charge

J.-M. Chung

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 133 | Cited 2 times

Online Publication Date: Jan 2008

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We use Jefimenko’s formulas to give an alternative derivation (without introducing vector and scalar potentials) for the fields of a suddenly moving sheet of charge (Feynman’s example). We also comment on the nonlocal nature of Jefimenko’s formulas.
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41.00.00 Electromagnetism; electron and ion optics

The wave-particle duality of light: A demonstration experiment

T. L. Dimitrova and A. Weis

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 137 | Cited 9 times

Online Publication Date: Jan 2008

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The wave-particle duality of light plays a fundamental role in introductory courses on quantum mechanics. Traditionally the wave and particle aspects of light are demonstrated in separate experiments which makes it difficult for students to understand their complementary nature. We present an experiment using a single apparatus that demonstrates the wave aspect, the particle aspect, and most importantly, their coexistence. The apparatus is based on a Mach-Zehnder interferometer in which a light beam is attenuated so that at each instant there is only a single photon in the interferometer. In this way the observation of single photon interference becomes possible. By integrating the single photon events in a storage oscilloscope the evolution toward classical interference fringes can be shown in real time. A second strong laser beam, derived from the same pointer, but slightly displaced, traverses the interferometer at the same time, allowing the simultaneous demonstration of wave aspects. Special features of the setup are low cost, simplicity, didactical power and suitability for presentations in large lecture halls using both multimedia projections and audible signals.
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01.50.Pa Laboratory experiments and apparatus
03.65.-w Quantum mechanics

Would Bohr be born if Bohm were born before Born?

Hrvoje Nikolić

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 143 | Cited 6 times

Online Publication Date: Jan 2008

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I discuss a hypothetical historical context in which a Bohm-like deterministic interpretation of the Schrödinger equation is proposed before the Born probabilistic interpretation and argue that in such a context the Copenhagen (Bohr) interpretation would probably have not achieved great popularity among physicists.
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01.65.+g History of science

Quantum entanglement, fair sampling, and reality: Is the moon there when nobody looks?

Guillaume Adenier

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 147 | Cited 6 times

Online Publication Date: Jan 2008

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In 1981 Mermin described a clever and simplified version of Bell’s theorem. He pointed out in a straightforward way that interpreting entanglement from a local realist point of view could be problematic. I propose an extended version of Mermin’s device that can be given a simple local realist interpretation by a sample selection bias. I argue that we still have no scientific reason to believe that the moon could not be there when nobody looks.
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01.70.+w Philosophy of science
03.65.-w Quantum mechanics

Classical and quantum behavior of dynamical systems defined by functions of solvable Hamiltonians

J. Fernando Barbero G., Iñaki Garay, and Eduardo J. S. Villaseñor

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 153 | Cited 1 time

Online Publication Date: Jan 2008

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We discuss the classical and quantum mechanical evolution of systems described by a Hamiltonian that is a function of a solvable one, both classically and quantum mechanically. The case in which the solvable Hamiltonian corresponds to the harmonic oscillator is emphasized. We show that, in spite of the similarities at the classical level, the quantum evolution is very different. In particular, this difference is important in constructing coherent states, which is impossible in most cases. The class of Hamiltonians we consider is interesting due to its pedagogical value and its applicability to some open research problems in quantum optics and quantum gravity.
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03.65.-w Quantum mechanics

Transition between short and long wavelength limits in quantum mechanical reflection from a linear potential

S. M. Kennedy, D. M. Paganin, and D. E. Jesson

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 158 | Cited 1 time

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The phase changes experienced by a wave reflected from an interface are a familiar fixture in introductory physics courses. Examples include the ±π phase shift acquired upon reflection from a hard mirror (for example, in thin film interference patterns and Newton’s rings) and the −π∕2 phase shift studied in soft mirror reflections (for example, in mirage ray paths and the WKB connection formulas). We focus on the transition between these two limits, where the phase change upon reflection evolves continuously between the limiting cases of −π and −π∕2. We study a simple quantum system that exhibits this transition: a one-dimensional free electron reflected from a linear potential.
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03.65.-w Quantum mechanics

Student understanding of control of variables: Deciding whether or not a variable influences the behavior of a system

Andrew Boudreaux, Peter S. Shaffer, Paula R. L. Heron, and Lillian C. McDermott

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 163 | Cited 4 times

Online Publication Date: Jan 2008

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The ability of adult students to reason on the basis of the control of variables was the subject of an extended investigation. This paper describes the part of the study that focused on the reasoning required to decide whether or not a given variable influences the behavior of a system. The participants were undergraduates taking introductory Physics and K–8 teachers studying physics and physical science in inservice institutes and workshops. Although most of the students recognized the need to control variables, many had significant difficulty with the underlying reasoning. The results indicate serious shortcomings in the preparation of future scientists and in the education of a scientifically literate citizenry. There are also strong implications for the professional development of teachers, many of whom are expected to teach control of variables to young students.
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01.40.Fk Research in physics education

Testing a new voting machine question methodology

N. W. Reay, Pengfei Li, and Lei Bao

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 171 | Cited 8 times

Online Publication Date: Jan 2008

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A new question methodology has been developed and used with voting machines in large physics lecture classrooms. The methodology was tested by comparing student performance in voting machine and non-voting machine lecture sections during three consecutive electricity and magnetism quarters of introductory calculus-based physics. Data from The Conceptual Survey of Electricity and Magnetism and common examination questions indicates that students using voting machines achieved a significant gain in conceptual learning, and that voting machines reduced the gap between male and female student performances on tests. Surveys indicated that students were positive about the use of voting machines and believed that they helped them learn. The surveys also suggested that grading voting machines responses and/or overusing voting machines may lower student enthusiasm.
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01.40.G- Curricula and evaluation
01.50.ht Instructional computer use

Promoting instructional change in new faculty: An evaluation of the physics and astronomy new faculty workshop

Charles Henderson

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 179 | Cited 5 times

Online Publication Date: Jan 2008

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An important finding of physics and astronomy education research (PAER) is that traditional, transmission-based instructional approaches are not effective in promoting meaningful student learning. Instead, PAER research suggests that physics and astronomy should be taught using more interactive instructional methods. These ways of teaching require significant changes in the way faculty think about teaching and learning and corresponding changes in their teaching behavior. Although the research base and corresponding pedagogies and strategies are well documented and widely available, widespread changes in physics and astronomy teaching at the college level has yet to occur. The Workshop for New Physics and Astronomy Faculty has been working to address this problem since 1996. This workshop, which is jointly administered by the American Association of Physics Teachers, the American Astronomical Society, and the American Physical Society, has attracted approximately 25% of all new physics and astronomy faculty each year to a four-day workshop designed to introduce new faculty to PAER-based instructional ideas and materials. This paper describes the impact of the Workshop as measured by surveys of Workshop participants and physics and astronomy department chairs. The results indicate that the Workshop is successful in meeting its goals and might be significantly contributing to the spread and acceptance of PAER-based instructional ideas and materials.
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01.40.G- Curricula and evaluation
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The driving mechanism for a Foucault pendulum (revisited)

Joseph Priest and Michael J. Pechan

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 188

Online Publication Date: Jan 2008

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Abstract Unavailable
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01.50.My Demonstration experiments and apparatus

Did Berkeley foreshadow Mach?

Ronald Newburgh

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 189

Online Publication Date: Jan 2008

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In a recent paper I discussed Mach’s rejection of Newtonian absolute space and motion and the role of Mach’s principle in relating the fixed stars to the source of inertia. The importance of Mach in Einstein’s development of the theory cannot be denied even though he later abandoned Mach’s principle. One hundred fifty years earlier Bishop Berkeley had also rejected Newton’s notions of absolute space and motion. I discuss the reason why I did not include Berkeley’s criticism of Newtonian absolute space in my recent paper.
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01.65.+g History of science

Concerning “hidden momentum”

Timothy H. Boyer

American Journal of Physics -- February 2008 -- Volume 76, Issue 2, pp. 190 | Cited 3 times

Online Publication Date: Jan 2008

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The concept of “hidden momentum” needs to be treated with care. An example of its misuse is given.
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41.00.00 Electromagnetism; electron and ion optics
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