AAPT Logo
AJP Logo
 
   
 

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

Dec 2007

Volume 75, Issue 12, pp. 1061-I16

back to top
RSS Feeds

ON BOOK REVIEW OF QUANTUM ENIGMA

Michael Nauenberg

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1061

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

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

REPLY TO NAUENBERG

N. David Mermin

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1061

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

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

REPLY TO NAUENBERG AND MERMIN

Fred Kuttner and Bruce Rosenblum

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1062

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

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

DECOHERENCE AND THE QUANTUM MEASUREMENT PROBLEM

Paul Meuffels

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1063

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
03.65.-w Quantum mechanics
back to top
RSS Feeds

Citations for the 2007 Robert A. Millikan Medal and the 2007 Klopsteg Memorial Award

Ken Heller

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1064

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
01.10.-m Announcements, news, and organizational activities
back to top
RSS Feeds

Arthur Compton’s 1941 Report on explosive fission of U-235: A look at the physics

B. Cameron Reed

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1065 | Cited 4 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In November 1941, the third of three reports on atomic fission commissioned by Vannevar Bush through the National Academy of Sciences examined the prospects for explosive fission in U-235. This report, prepared by Arthur Compton, developed a model for estimating the critical mass and efficiency of an atomic bomb. I examine Compton’s physics, attempt to discern the provenance of the numbers he adopted for various parameters, and compare his results with those yielded by a full diffusion-theory approach with contemporary values for the fission parameters. I conclude that Compton’s physics is sound. A combination of somewhat optimistic parameter values and a conservative model for critical mass lead him to a numerical value for the bare critical radius of U-235 that is in fairly good accord with that yielded by diffusion theory. His estimated efficiency proved to be quite accurate for the Little Boy bomb.
Show PACS
01.65.+g History of science
20.00.00 NUCLEAR PHYSICS

Experimental study of the frequency repulsion effect

R. F. Gamarra, M. Josebachuili, P. Zurita, and S. Gil

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1073 | Cited 3 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We discuss an experiment on coupled RLC circuits with variable coupling strength. The inductive coupling can be easily varied and measured for different configurations. The experiment allows us to explore the variation of the resonance frequencies as a function of the coupling strength between the oscillators. The system illustrates the effect of eigenfrequency repulsion when an interaction couples different modes of oscillation. The experiment is conceptually simple, and its results can be compared quantitatively with theoretical predictions.
Show PACS
01.50.Pa Laboratory experiments and apparatus
84.00.00 Electronics; radiowave and microwave technology; direct energy conversion and storage

Understanding Langmuir probe current-voltage characteristics

Robert L. Merlino

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1078 | Cited 9 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
I give several simple examples of model Langmuir probe current-voltage (I-V) characteristics that help students learn how to interpret real I-V characteristics obtained in a plasma. Students can also create their own Langmuir probe I-V characteristics using a program with the plasma density, plasma potential, electron temperature, ion temperature, and probe area as input parameters. Some examples of Langmuir probe I-V characteristics obtained in laboratory plasmas are presented and analyzed. A few comments are made advocating the inclusion of plasma experiments in the advanced undergraduate laboratory.
Show PACS
01.50.Pa Laboratory experiments and apparatus
50.00.00 PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Thermodynamics of a pure substance at the triple point

S. Velasco and C. Fernández-Pineda

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1086

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A thermodynamic study of a pure substance at the triple point is presented. In particular, we show that the mass fractions of the phases coexisting at the triple point obey lever rules in the specific entropy-specific volume diagram, and the relative changes in the mass fractions present in each phase along reversible isochoric and adiabatic processes of a pure substance at the triple point are governed by the relative sizes of the segments of the triple-point line in the pressure-specific volume diagram and in the temperature-specific entropy diagram. Applications to the ordinary triple point of water and to the triple point of Al2SiO5 polymorphs are presented.
Show PACS
05.70.-a Thermodynamics

Vortex flow generated by a magnetic stirrer

Gábor Halász, Balázs Gyüre, Imre M. Jánosi, K. Gábor Szabó, and Tamás Tél

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1092 | Cited 5 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate the flow generated by a magnetic stirrer in cylindrical containers by optical observations, particle image velocimetry measurements, and particle and dye tracking methods. The tangential flow is that of an ideal vortex outside a core, but inside downwelling occurs with a strong jet in the very middle. In the core region dye patterns remain visible over minutes indicating inefficient mixing in this region. The results of quantitative measurements can be described by simple relations that depend on the stirring bar’s rotation frequency. The tangential flow is similar to that of large atmospheric vortices such as dust devils and tornadoes.
Show PACS
47.00.00 Fluid dynamics

An experimental study of Wiffle ball aerodynamics

Jenn Rossmann and Andrew Rau

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1099 | Cited 1 time

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We measure the aerodynamic forces on a Wiffle ball as a function of the Reynolds number and ball orientation. The effects of asymmetric flow outside the ball and flow within the ball are considered, and are both associated with the ball’s tendency to curve without pitcher-imparted spin. The problem of Wiffle ball aerodynamics is an accessible way to introduce topics such as boundary layer separation and transition to turbulence.
Show PACS
01.50.Pa Laboratory experiments and apparatus
01.55.+b General physics
47.00.00 Fluid dynamics

How to teach friction: Experiments and models

Ugo Besson, Lidia Borghi, Anna De Ambrosis, and Paolo Mascheretti

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1106 | Cited 6 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Students generally have difficulty understanding friction and its associated phenomena. High school and introductory college-level physics courses usually do not give the topic the attention it deserves. We have designed a sequence for teaching about friction between solids based on a didactic reconstruction of the relevant physics, as well as research findings about student conceptions. The sequence begins with demonstrations that illustrate different types of friction. Experiments are subsequently performed to motivate students to obtain quantitative relations in the form of phenomenological laws. To help students understand the mechanisms producing friction, models illustrating the processes taking place on the surface of bodies in contact are proposed.
Show PACS
01.40.G- Curricula and evaluation

The Malkus–Lorenz water wheel revisited

Leslie E. Matson

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1114 | Cited 4 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The Malkus–Lorenz water wheel is analyzed in a more direct way. Two new dimensionless parameters associated with properties of the water wheel are used in place of the traditional Lorenz parameters, which relate only to Lorenz’s fluid model. The primary result is a performance map in the new dimensionless parameter space, which shows where the major behavior types occur and associated bifurcations. A slice across this map is examined by a bifurcation plot that shows details of the transitions between various types of behavior. An example of a 12-cup water wheel model is provided, and its behavior is compared over a wide range of parameters on the performance map to that of the Malkus-Lorenz water wheel. It is shown how the map with its water wheel parameters can be simply converted to the map with Lorenz’s fluid dynamics parameters.
Show PACS
05.45.-a Nonlinear dynamics and chaos

Two examples of circular motion for introductory courses in relativity

Stephanie Wortel, Shimon Malin, and Mark D. Semon

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1123 | Cited 4 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF


See Also: Erratum

Show Abstract
The circular twin paradox and Thomas precession are presented in a way that makes them accessible to students in introductory relativity courses. Both are discussed by examining what happens during travel around a polygon and then in the limit as the polygon becomes a circle. Because relativistic predictions based on these examples are verified in experiments with macroscopic objects (such as atomic clocks flown in airplanes and the gyroscopes on Gravity Probe B), they are especially convincing to introductory students.
Show PACS
03.30.+p Special relativity

Relativity and mathematical tools: Waves in moving media

Martin McCall and Dan Censor

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1134 | Cited 5 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We discuss the electromagnetic wave equation and dispersion relation for moving media as an example of the challenge of integrating vectors and dyadics and their covariant counterparts into the teaching of special relativity. We discuss two methods of deriving the dispersion relation and its associated wave equation. One is a direct approach for which the starting point is Maxwell’s equations combined with the Minkowski constitutive relations in the laboratory frame Γ in which the medium is moving uniformly. The second approach, starting in the medium’s rest frame Γ′, establishes the invariance properties of the dispersion relation, and then proceeds to derive its counterpart in Γ. Application to the calculation of the group velocity in each frame is also discussed.
Show PACS
03.30.+p Special relativity
41.00.00 Electromagnetism; electron and ion optics

Combined electric and magnetic Aharonov–Bohm effects

Samuel Marcovitch, Yakir Aharonov, Tirza Kaufferr, and Benni Reznik

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1141

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
It is well known that the electric and magnetic Aharonov–Bohm effects may be formally described on an equal footing using the four-vector potential in a relativistic framework. We give an illustrative manifestation of both effects in a single configuration in which the path of the charged particle determines the weight of the acquired electric and magnetic relative phases. The phases can be distinctively obtained in the Coulomb gauge. The examples illustrate that, although each of the relative phases is gauge dependent, their sum is gauge invariant.
Show PACS
03.65.-w Quantum mechanics

Relativistic dynamics of the deuteron: An estimate of the nuclear force parameters

L. Di G. Sigalotti and A. Mejias

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1147

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A relativistic dynamical model of the deuteron nucleus is presented. The neutron and proton are assumed to interact via a short-range Yukawa interaction of strength g2. A close parallel between the Bohr model of the hydrogen atom and the deuteron nucleus is established by quantizing the angular momentum for the Yukawa interaction in the same way that is done for the Coulomb interaction. The measured value of the deuteron binding energy for circular orbits is used to calculate the coupling constant g2, the tangential velocity of the component nucleons, and their separation. The results compare favorably with those obtained employing more sophisticated methods. By using the experimentally known root-mean-square radius of the electric charge of the deuteron, the model is also used to estimate the mean radius of the proton. The model highlights many important features of the nuclear force from basic principles.
Show PACS
20.00.00 NUCLEAR PHYSICS

Reflectionless eigenstates of the sech2 potential

John Lekner

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1151 | Cited 21 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The one-dimensional potential well V(x)=−(ℏ2ν(ν+1)∕2ma2) sech2(x∕a) does not reflect waves of any energy when ν is a positive integer. We show that in this reflectionless case the solutions of Schrödinger’s equation can be expressed in terms of elementary functions. Wave packets can be constructed from these energy eigenstates, and the propagation of such wave packets through the potential region can be studied analytically. We find that the group velocity of a particular packet can substantially exceed the group velocity of a free-space Gaussian packet. The bound states of the potential can also be expressed in terms of elementary functions when ν is an integer. The special properties of the integer ν potentials are associated with critical binding.
Show PACS
03.65.-w Quantum mechanics

Bistable transmission of plane waves across two nonlinear delta functions

P. S. Moya, Max Ramírez, and M. I. Molina

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1158

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We examine the transmission coefficient of plane waves across two nonlinear delta-function barriers with positive opacity. It is shown that this simple system is capable of bistable behavior at sufficiently large input intensities. The bistable behavior is centered around the first transmission resonances and is a simple example of a continuum nonlinear system that can display bistability without the presence of a feedback loop.
Show PACS
03.65.-w Quantum mechanics
05.45.-a Nonlinear dynamics and chaos

The role of the density operator in the statistical description of quantum systems

Jamshid Sabbaghzadeh and Ali Dalafi

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1162 | Cited 2 times

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A quantum mechanical system that is described by a state vector can be equally described by a density operator, although the inverse is not true. When information about a system is incomplete the only way to describe the system is by the density operator formalism. Incompleteness arises in two general cases: a mixed ensemble of physical systems and a system that interacts with its environment. We shed light on some subtle points that are usually misunderstood. We show explicitly that in the first case the averaged state vector of the system is zero, and in the second case no state vector can be assigned to the system in general.
Show PACS
03.65.-w Quantum mechanics
05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems
back to top
RSS Feeds

Comment on “The role of mediation in collisions and related analogs,” by E. Bashkansky and N. Netzer [Am. J. Phys. 74 (12), 1083–1087 (2006)]

Massimiliano Sassoli de Bianchi

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1166

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
47.00.00 Fluid dynamics
back to top
RSS Feeds

BOOKS RECEIVED

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. 1167

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
back to top
RSS Feeds

Volume 75 Index

American Journal of Physics -- December 2007 -- Volume 75, Issue 12, pp. I1

Online Publication Date: Nov 2007

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Close

AAPT on:

close