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Dec 2004

Volume 72, Issue 12, pp. 1465-1531

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The physics of bat echolocation: Signal processing techniques

Mark Denny

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1465 | Cited 3 times

Online Publication Date: Nov 2004

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The physical principles and signal processing techniques underlying bat echolocation are investigated. It is shown, by calculation and simulation, how the measured echolocation performance of bats can be achieved. © 2004 American Association of Physics Teachers.
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01.50.-i Educational aids
87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction
87.50.Y- Biological effects of acoustic and ultrasonic energy

Challenges to Faraday’s flux rule

Frank Munley

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1478 | Cited 7 times

Online Publication Date: Nov 2004

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Faraday’s law (or flux rule) is beautiful in its simplicity, but difficulties are often encountered when applying it to specific situations, particularly those where points making contact to extended conductors move over finite time intervals. These difficulties have led some to challenge the generality of the flux rule. The challenges are usually coupled with the claim that the Lorentz force law is general, even though proofs have been given of the equivalence of the two for calculating instantaneous emfs in well-defined filamentary circuits. I review a rule for applying Faraday’s law, which says that the circuit at any instant must be fixed in a conducting material and must change continuously. The rule still leaves several choices for choosing the circuit. To explicate the rule, it will be applied to several challenges, including one by Feynman. © 2004 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Torque or no torque? Simple charged particle motion observed in different inertial frames

J. D. Jackson

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1484 | Cited 3 times

Online Publication Date: Nov 2004

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In a given inertial frame, a charged particle initially at rest moves in the central electric field caused by a fixed charge at the origin. The particle has no initial angular momentum and experiences no torque. However, in an inertial frame moving with a nonvanishing velocity with respect to the first, the charged particle’s motion is subject to the Lorentz force with both electric and magnetic fields produced by the “fixed” charge, which is now in uniform motion. The charged particle experiences a torque from the magnetic part of the force; its nonvanishing angular momentum changes in time. This puzzle is analyzed in detail from different reference frames. The chief characteristic of the motion, independent of the choice of the inertial frame, is the constancy in time of the orientation of the relative coordinate r as the particle moves with respect to the fixed (or uniformly moving) charge. © 2004 American Association of Physics Teachers.
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01.50.-i Educational aids
03.30.+p Special relativity
41.00.00 Electromagnetism; electron and ion optics

The Hertz contact in chain elastic collisions

P. Patrício

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1488 | Cited 2 times

Online Publication Date: Nov 2004

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A theoretical analysis of the influence of the Hertz elastic contact on a three body chain collision is presented. Despite the elastic character of the collision, the final velocity of each particle depends on the interaction between them. Two elastic spheres falling together, one on top of the other under the action of gravity, and then colliding with the ground, are studied in detail. © 2004 American Association of Physics Teachers.
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01.50.-i Educational aids
45.50.Tn Collisions

A billiard-theoretic approach to elementary one-dimensional elastic collisions

S. Redner

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1492 | Cited 5 times

Online Publication Date: Nov 2004

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A simple relation is developed between the elastic collisions of freely moving particles in one dimension and a corresponding billiard system. For two particles with masses m1 and m2 on the half-line x>0 that approach an elastic barrier at x=0, the corresponding billiard system is an infinite wedge. The collision history of the two particles can be easily inferred from the corresponding billiard trajectory. This connection explains the classic demonstrations of the “dime on the superball” and the “baseball on the basketball” that are a staple in elementary physics courses. It also is shown that three elastic particles on an infinite line and three particles on a finite ring correspond, respectively, to the motion of a billiard ball in an infinite wedge and on a triangular billiard table. It is shown how to determine the angles of these two sets in terms of the particle masses. © 2004 American Association of Physics Teachers.
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01.50.My Demonstration experiments and apparatus
01.40.E- Science in school
45.05.+x General theory of classical mechanics of discrete systems
45.50.Tn Collisions

Force on a dielectric slab: Fringing field approach

Eric R. Dietz

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1499 | Cited 2 times

Online Publication Date: Nov 2004

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The calculation of the force on a dielectric material partially inserted between two parallel charged conducting plates, typically done in undergraduate classrooms using energy considerations, is performed by explicitly considering the effect of the fringing electric field. © 2004 American Association of Physics Teachers.
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01.50.My Demonstration experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems

Understanding the Fano resonance through toy models

Swarnali Bandopadhyay, Binayak Dutta-Roy, and H. S. Mani

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1501 | Cited 5 times

Online Publication Date: Nov 2004

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The Fano resonance involves the mixing between the continuum states of the elastic channel and a quasi-bound discrete state of the inelastic channel. The underlying ideas have recently attracted attention in connection with interference effects in quantum wires and mesoscopic transport phenomena. Simple toy models are discussed to illustrate the subtle aspects of the Fano resonance. © 2004 American Association of Physics Teachers.
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01.40.-d Education
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.65.La Quantum wires (patterned in quantum wells)
73.23.-b Electronic transport in mesoscopic systems

Rocking Newton’s cradle

Stefan Hutzler, Gary Delaney, Denis Weaire, and Finn MacLeod

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1508 | Cited 7 times

Online Publication Date: Nov 2004

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In textbook descriptions of Newton’s cradle, it is generally claimed that displacing one ball will result in a collision that leads to another ball being ejected from the line, with all others remaining motionless. Hermann and Schmälzle, Hinch and Saint-Jean, and others have shown that a realistic description is more subtle. We present a simulation of Newton’s cradle that reproduces the break-up of the line of balls at the first collision, the eventual movement of all the balls in phase, and is in good agreement with our experimentally obtained data. The first effect is due to the finite elastic response of the balls, and the second is a result of viscoelastic dissipation in the impacts. We also analyze a dissipation-free ideal Newton’s cradle which displays complex dynamics. © 2004 American Association of Physics Teachers.
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01.50.My Demonstration experiments and apparatus
45.40.-f Dynamics and kinematics of rigid bodies
45.05.+x General theory of classical mechanics of discrete systems

Absence of convection in a perfect gas

Alessandro Ciattoni, Paolo Di Porto, and Bruno Crosignani

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1517

Online Publication Date: Nov 2004

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We investigate the conditions under which a perfect gas subject to a three-dimensional external conservative field is in mechanical equilibrium without being in thermal equilibrium, that is, with a nonvanishing temperature gradient. We find the class of potentials for which this behavior is possible. In particular, gravitational, Coulomb, and centrifugal fields are shown to belong to this class. We obtain the functional form of the temperature field that assures the absence of convection and obtain the stability condition for mechanical equilibrium. © 2004 American Association of Physics Teachers.
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01.40.-d Education
51.30.+i Thermodynamic properties, equations of state

Use of the Einstein–Brillouin–Keller action quantization

Lorenzo J. Curtis and David G. Ellis

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1521 | Cited 9 times

Online Publication Date: Nov 2004

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The Einstein–Brillouin–Keller semiclassical quantization and the topological Maslov index are used to deduce the correct quantum mechanical values for the energy of a one-electron atom (both nonrelativistically and relativistically) and a three-dimensional harmonic oscillator. The development is concise, transparent, and involves only elementary integral calculus and provides a conceptual and intuitive introduction to the quantum nature of the atomic and molecular structure of matter. © 2004 American Association of Physics Teachers.
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01.50.-i Educational aids
03.65.Sq Semiclassical theories and applications
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
03.65.Ge Solutions of wave equations: bound states
03.65.Vf Phases: geometric; dynamic or topological

Simplified derivation of the Hawking–Unruh temperature for an accelerated observer in vacuum

Paul M. Alsing and Peter W. Milonni

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1524 | Cited 9 times

Online Publication Date: Nov 2004

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A detector undergoing uniform acceleration a in a vacuum field responds as though it were immersed in thermal radiation of temperature T=ℏa/2πkc. An intuitive derivation of this result is given for a scalar field in one spatial dimension. The approach is extended to the case where the field detected by the accelerated observer is a spin 1/2 Dirac field. © 2004 American Association of Physics Teachers.
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01.40.-d Education
04.62.+v Quantum fields in curved spacetime
04.70.Dy Quantum aspects of black holes, evaporation, thermodynamics
44.40.+a Thermal radiation
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Comment on “The distribution of composite measurements: How to be certain of the uncertainties in what we measure,” by M. P. Silverman, W. Strange, and T. C. Lipscombe [Am. J. Phys. 72 (8), 1068–1081 (2004)]

F. A. B. Coutinho, L. F. Lopez, and E. Massad

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1530

Online Publication Date: Nov 2004

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© 2004 American Association of Physics Teachers.
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01.50.-i Educational aids
06.20.Dk Measurement and error theory
02.50.Cw Probability theory

Erratum: “Photolithographic fabrication of diffraction and interference slit patterns for the undergraduate laboratory” [Am. J. Phys. 72 (10), 1328–1334 (2004)]

Harriet Slogoff, Jeff Mackowiak, Milen Shishkov, and Alan T. Johnson

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1530

Online Publication Date: Nov 2004

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© 2004 American Association of Physics Teachers.
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99.10.Cd Errata
01.50.Pa Laboratory experiments and apparatus
42.82.Cr Fabrication techniques; lithography, pattern transfer
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Modern Classical Optics

Geoffrey Brooker and Alma C. Zook, Reviewer

American Journal of Physics -- December 2004 -- Volume 72, Issue 12, pp. 1531

Online Publication Date: Nov 2004

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Abstract Unavailable
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01.30.Vv Book reviews
01.50.My Demonstration experiments and apparatus
01.40.Di Course design and evaluation
42.40.-i Holography
42.79.Dj Gratings
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