AAPT Logo
AJP Logo
 
   
 

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

Feb 2012

Volume 80, Issue 2, pp. 101-176

back to top
RSS Feeds

SYMMETRY AND VOLTMETERS

Bart H. McGuyer

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 101

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
41.00.00 Electromagnetism; electron and ion optics
back to top
RSS Feeds

Resource Letter AFHEP-1: Accelerators for the Future of High-Energy Physics

William A. Barletta

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 102

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This Resource Letter provides a guide to literature concerning the development of accelerators for the future of high-energy physics. Research articles, books, and Internet resources are cited for the following topics: motivation for future accelerators, present accelerators for high-energy physics, possible future machine, and laboratory and collaboration websites.
Show PACS
01.30.Rr Surveys and tutorial papers; resource letters
29.20.-c Accelerators

Chaotic motors

C. Laroche, R. Labbé, F. Pétrélis, and S. Fauve

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 113

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We show that electric motors and dynamos can be used to illustrate most elementary instabilities or bifurcations discussed in courses on nonlinear oscillators and dynamical systems. These examples are easier to understand and display a richer behavior than the ones commonly used from mechanics, electronics, hydrodynamics, lasers, chemical reactions, and population dynamics. In particular, an electric motor driven by a dynamo can display stationary, Hopf, and codimension-two bifurcations by tuning the driving speed of the dynamo and the electric current in the stator of the electric motor. When the dynamo is driven at constant torque instead of constant rotation rate, chaotic reversals of the generated current and of the angular rotation of the motor are observed. Simple deterministic models are presented which capture the observed dynamical regimes.
Show PACS
05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems

Near-field light focusing by a slit array in a planar metal film with nonuniform slit dielectric material

L. David Wellems and Danhong Huang

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 122

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We study the interference of evanescent electromagnetic waves generated from multi-slits in a metal film and demonstrate the anomalous bending of light at infrared frequencies due to negative refraction. We also calculate the diffraction of an incident plane electromagnetic waves by a metallic film with an arbitrary linear array of slits, slit separation, and slit dielectric material. In contrast to a double-convex shaped quartz lens, we show that a planar metallic film with a one-dimensional slit array can also focus polarized light in the near-field region when either the slit width or the slit dielectric material becomes spatially nonuniform.
Show PACS
40.00.00 ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Undergraduate experiment in superconductor point-contact spectroscopy with a Nb/Au junction

Lucas Janson, Matthew Klein, Heather Lewis, Andrew Lucas, Andrew Marantan, and Katherine Luna

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 133

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We describe an experiment in superconductivity suitable for an advanced undergraduate laboratory. Point-contact spectroscopy is performed by measuring the differential conductance between an electrochemically etched gold tip and a 100-nm thick superconducting niobium film with a transition temperature Tc ≈ 7 K. By fitting the results to Blonder–Tinkham–Klapwijk theory using a finite lifetime of quasiparticles, we obtain a superconducting gap energy Δ ≈ 1.53 meV, a lower bound to the Fermi velocity vF ≥ 3.1 × 107 cm/s, and a BCS coherence length ξ ≈ 43 nm for niobium. These results are in good agreement with previous measurements.
Show PACS
01.50.Pa Laboratory experiments and apparatus
74.00.00 Superconductivity

On Klein tunneling in graphene

T. R. Robinson

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 141

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The essential features of Klein tunneling of massless fermions in graphene may be treated in one dimension without the need for Dirac spinors. Two dimensions needs a spinor treatment and is investigated numerically, which lets us compare tunneling through smooth potential barriers with that through idealized step potentials.
Show PACS
03.65.-w Quantum mechanics

A new multimedia resource for teaching quantum mechanics concepts

Antje Kohnle, Donatella Cassettari, Tom J. Edwards, Callum Ferguson, Alastair D. Gillies, Christopher A. Hooley, Natalia Korolkova, Joseph Llama, and Bruce D. Sinclair

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 148

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We describe a collection of interactive animations and visualizations for teaching quantum mechanics. The animations can be used at all levels of the undergraduate curriculum. Each animation includes a step-by-step exploration that explains the key points. The animations and instructor resources are freely available. By using a diagnostic survey, we report substantial learning gains for students who have worked with the animations.
Show PACS
01.50.ht Instructional computer use
03.65.-w Quantum mechanics

Student understanding of energy: Difficulties related to systems

Beth A. Lindsey, Paula R. L. Heron, and Peter S. Shaffer

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 154

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Choosing a system of interest and identifying the interactions of the system with its environment are crucial steps in applying the relation between work and energy. Responses to problems that we administered in introductory calculus-based physics courses show that many students fail to recognize the implications of a particular choice of system. In some cases, students do not believe that particular groupings of objects can even be considered to be a system. Some errors are more prevalent in situations involving gravitational potential energy than elastic potential energy. The difficulties are manifested in both qualitative and quantitative reasoning.
Show PACS
01.40.Fk Research in physics education

Meissner effect, diamagnetism, and classical physics—a review

Hanno Essén and Miguel C. N. Fiolhais

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 164

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We review the literature on what classical physics says about the Meissner effect and the London equations. We discuss the relevance of the Bohr-van Leeuwen theorem for the perfect diamagnetism of superconductors and conclude that the theorem is based on invalid assumptions. We also point out results in the literature that show how magnetic flux expulsion from a sample cooled to superconductivity can be understood as an approach to the magnetostatic energy minimum. These results have been published several times but many textbooks on magnetism still claim that there is no classical diamagnetism, and virtually all books on superconductivity repeat Meissner’s 1933 statement that flux expulsion has no classical explanation.
Show PACS
01.30.Rr Surveys and tutorial papers; resource letters
74.00.00 Superconductivity
back to top
RSS Feeds

Comment on “The Gibbs paradox and the distinguishability of identical particles,” by M. A. M. Versteegh and D. Dieks [Am. J. Phys. 79, 741–746 (2011)]

David S. Corti

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 170

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We revisit recent discussions concerning the Gibbs paradox—the apparent discrepancy between the entropy change upon mixing identical gases as evaluated from the statistical mechanics of classical distinguishable particles and macroscopic thermodynamics. Contrary to what is often stated, we show that thermodynamics does not require this entropy of mixing to be zero. A zero value follows from the implicit assumption that the identical gas particles are indistinguishable. If the identical particles are explicitly assumed to be distinguishable, thermodynamics yields the same entropy of mixing as classical statistical mechanics.
Show PACS
05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems
back to top
RSS Feeds

The Physics of the Human Body.

Richard P. McCall and Marc Sher, Reviewer

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 174

Full Text: | Download PDF

Abstract Unavailable
Show PACS
01.30.Vv Book reviews
01.55.+b General physics

Quantitative Understanding of Biosystems: An Introduction to Biophysics.

Thomas M. Nordlund and Liviu Movileanu, Reviewer, Reviewer

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 175

Full Text: | Download PDF

Abstract Unavailable
Show PACS
01.30.Vv Book reviews
87.00.00 Biological and medical physics

BOOKS RECEIVED

American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 176

Full Text: | Download PDF

Abstract Unavailable
Close

AAPT on:

close