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Sep 1990

Volume 58, Issue 9, pp. 807-895

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Physics need not be difficult

V. Srinivasan

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 807

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Abstract Unavailable
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01.40.-d Education

Will perestroika and glasnost come to APS?

Lawrence Cranberg

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 807

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01.10.Hx Physics organizational activities

Variation in the length of the synodic month

Donald W. Olson

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 807

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96.20.-n Moon
95.10.Gi Eclipses, transits, and occultations
01.30.Ee Monographs and collections

Physicists’ arrogance and Jacques Derrida

J. Apple Henry

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 808

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Abstract Unavailable
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01.75.+m Science and society
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Guest Comment: Physics, physics students, and Tiananmen Square

Fang Lizhi

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 809

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Abstract Unavailable
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01.75.+m Science and society
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A dynamic method of measuring the charge induced on a conductor

Cyrus S. MacLatchy and Hugh A. Chipman

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 811 | Cited 1 time

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A simple method of measuring the charge induced on a conductor is presented. The method is based on the idea that a charged projectile passing near a conducting object will cause surface charges to be dynamically induced on its surface. By suitably arranging a detector in the surface of the object, the charge drawn onto the conductor during the passage of the charged projectile can be measured and related to the induced surface charge density. The charge is computed by integrating the current waveform. The concept has been used to design a detector that measures the charge induced on a high‐speed projectile such as a pellet fired from an air rifle, the charge induced on a raised hemispherical boss by a uniform electric field, and the surface charge induced on a flat plate by a point charge.
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01.50.Pa Laboratory experiments and apparatus
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Poetry for physicists

Sheila Tobias and Lynne S. Abel

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 816

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In an effort to discover what makes the humanities difficult and unpopular with some science and engineering students, 14 Cornell faculty from the disciplines of chemistry, physics, applied mathematics, geology, materials science, and engineering were invited to become ‘‘surrogate learners’’ in a junior/senior level poetry seminar designed expressly for them. Their encounter with humanistic pedagogy and scholarship was meant to be an extension of ‘‘Peer Perspectives on Science’’ [see S. Tobias and R. R. Hake, ‘‘Professors as physics students: What can they teach us?’’ Am. J. Phys. 56, 786 (1988)]. The results challenge certain assumptions about differences between scholarship and pedagogy in the humanities and science (as regards ‘‘certainty’’ and models). But the experiment uncovered other problems that affect ‘‘marketing’’ the humanities to science and engineering students. Results are some additional insights into what makes science ‘‘hard’’ for humanities students and why physical science and engineering students have difficulty with and tend to avoid courses in literature, as well as into what can make humanities courses valuable for science students.
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01.40.G- Curricula and evaluation

The twin paradox revisited

Tevian Dray

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 822 | Cited 2 times

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The twin paradox of special relativity results from failing to recognize the fundamental asymmetry between the two twins: One and only one twin changes direction and thus undergoes acceleration. What happens if the universe is closed, so that the twin in the rocket can return to Earth without changing direction? The twin paradox is reformulated in a closed universe (a cylinder) and then resolved by showing that there is still a (much more subtle!) asymmetry between the two twins.
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03.30.+p Special relativity

The Bohr–Einstein ‘‘weighing‐of‐energy’’ debate and the principle of equivalence

Richard J. Hughes

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 826

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The Bohr–Einstein debate over the ‘‘weighing of energy’’ and the validity of the time–energy uncertainty relation is reexamined in the context of gravitation theories that do not respect the equivalence principle. Bohr’s use of the equivalence principle is shown to be sufficient, but not necessary, to establish the validity of this uncertainty relation in Einstein’s ‘‘weighing‐of‐energy’’ gedanken experiment. The uncertainty relation is shown to hold in any energy‐conserving theory of gravity, and so a failure of the equivalence principle does not engender a failure of quantum mechanics. The relationship between the gravitational redshift and the equivalence principle is reviewed.
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03.65.Ta Foundations of quantum mechanics; measurement theory
04.20.Cv Fundamental problems and general formalism

Everett’s theory and the ‘‘many‐worlds’’ interpretation

Yoav Ben‐Dov

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 829

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A distinction is made between the ‘‘popular many‐worlds interpretation’’ and Everett’s ‘‘relative state’’ formulation of quantum mechanics. This distinction is claimed to be relevant to arguments raised against both schemes.
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03.65.Ta Foundations of quantum mechanics; measurement theory

Wilberforce’s pendulum revisited

Ulrich Köpf

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 833 | Cited 1 time

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If its radius of gyration is properly tuned, a mass attached to a simple helical spring is able to perform longitudinal and torsional oscillations that are coupled with one another and exhibit the beats characteristic to coupled oscillations. The mechanism of coupling as well as the corresponding differential equations are derived. For the case of resonance, the solutions are compared with experimental results.
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45.05.+x General theory of classical mechanics of discrete systems
07.10.-h Mechanical instruments and equipment

Oscillations of a dipole in a magnetic field: An experiment

Juan Bisquert, Emilia Hurtado, Salvador Mafé, and José Pina

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 838 | Cited 2 times

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The small oscillations of a parallelepidal magnet along the axis of a circular coil carrying an electric current have been analyzed theoretically and experimentally. The study of this system (a particular case of a magnetic dipole in motion in a nonuniform magnetic field) involves basic ideas from both mechanics and electromagnetism, and the equipment used in the experiment is very common in an undergraduate laboratory. Comparison with the experiment shows that a very simple theoretical approach gives good results. It is also shown how the introduction of some refinements in the physical model can improve the agreement between theory and experiment, though the theoretical analysis becomes more involved in this case. The use of the principle of superposition to calculate magnetic fields is emphasized throughout the article.
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01.50.Pa Laboratory experiments and apparatus
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Simulation of wave propagation in dispersive media using FFT

A. Albareda, E. Toribio, J. A. Gorri, and R. Pérez

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 844

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A method to show the temporal evolution of wavefunctions in linear lossless media is developed by using the inverse fast Fourier transform. Sequential images of the wave patterns are obtained by assuming simple phase functions for different dispersion relations, and for any given kind of spectra. The evolution of a wave packet shows the different group and phase velocities, and the deformation and spreading of the envelope in several dispersive media.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation

Generating functions and the statistics of radioactive chains

Javier Vitela E. and Manuel Coronado

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 849

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The statistics of a radioactive chain composed of father nuclei decaying into two daughter nuclei is analyzed. To illustrate the usefulness of generating functions, a master equation is used for the probability density and then an equation is derived and solved for the corresponding generating function. From this function the time evolution of the probability density is obtained. Two cases are considered: (1) when an external source gives rise to the father nuclei and (2) with no external source present. The effect of different initial conditions is also analyzed. The results clarify some misleading statements appearing in the literature, and provide teachers with interesting examples of the use of generating functions.
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23.90.+w Other topics in radioactive decay and in-beam spectroscopy (restricted to new topics in section 23)
02.50.Fz Stochastic analysis

The gravitational red shift in a uniform field

Edward A. Desloge

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 856 | Cited 1 time

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When a photon is transmitted from a source S through a uniform gravitational field for which the acceleration due to gravity is g to a detector D located a distance h above S, the frequency νD of the photon measured at the detector is less than the frequency νS measured at the source. The various assumptions and approximations employed in textbook analyses of this phenomenon are considered. The exact dependence of νD on νS, g, and h is then determined first on the conventional assumption that the frequency shift in a uniform gravitational field is the same as the frequency shift in a uniformly accelerating reference frame in field‐free space and, second, on the more valid assumption that space‐time is curved in a uniform gravitational field and the frequency shift in the field is a consequence of the space‐time curvature. The expressions obtained depend not only on which of the above assumptions is made but also on the exact interpretation of the quantities g and h.
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04.40.-b Self-gravitating systems; continuous media and classical fields in curved spacetime

Learning motion concepts using real‐time microcomputer‐based laboratory tools

Ronald K. Thornton and David R. Sokoloff

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 858 | Cited 17 times

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Microcomputer‐based laboratory (MBL) tools have been developed which interface to Apple II and Macintosh computers. Students use these tools to collect physical data that are graphed in real time and then can be manipulated and analyzed. The MBL tools have made possible discovery‐based laboratory curricula that embody results from educational research. These curricula allow students to take an active role in their learning and encourage them to construct physical knowledge from observation of the physical world. The curricula encourage collaborative learning by taking advantage of the fact that MBL tools present data in an immediately understandable graphical form. This article describes one of the tools—the motion detector (hardware and software)—and the kinematics curriculum. The effectiveness of this curriculum compared to traditional college and university methods for helping students learn basic kinematics concepts has been evaluated by pre‐ and post‐testing and by observation. There is strong evidence for significantly improved learning and retention by students who used the MBL materials, compared to those taught in lecture.
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01.50.ht Instructional computer use
01.50.Qb Laboratory course design, organization, and evaluation
07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation

A plea for a correct translation of Newton’s law of inertia

Erwin Marquit

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 867

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The formulations of Newton’s law of inertia in university‐level textbooks usually follow the Motte–Cajori translation of Newton’s Principia. The rich content of Newton’s law of inertia as a causality principle for mechanics is partly hidden by Motte’s mistranslation of the Latin phrase nisi quatenus as unless instead of except insofar as. One effect of this error is a tendency to isolate from the law some of the ‘‘Definitions’’ that precede Newton’s statement of the three laws of motion. These definitions, when taken together with the laws, provide the basis for Newton’s quantitative and qualitative elaboration of the coupled concepts of mass and force.
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01.65.+g History of science
45.05.+x General theory of classical mechanics of discrete systems

Optical fiber sensor experiments for the undergraduate physics laboratory

R. M. Bunch

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 870 | Cited 1 time

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Two experiments, suitable for a 3‐h undergraduate laboratory period, employing optical fibers as position sensors are described. These two experiments are based on microbending losses in the fiber and on an external moving reflector, respectively. For each case a model that characterizes the behavior of the transmitted light output from the sensor is given. A knowledge of the model and subsequent analysis for each sensor provide natural experiments suitable for an undergraduate physics/optics laboratory.
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01.50.Pa Laboratory experiments and apparatus
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.81.Pa Sensors, gyros
42.81.Dp Propagation, scattering, and losses; solitons

Measurement of thermal expansion coefficients using a strain gauge

John N. Fox

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 875

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A strain gauge is employed to determine the coefficient of thermal expansion of a solid. The apparatus is interfaced to a computer to obtain a linear plot of displacement against temperature.
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01.50.Pa Laboratory experiments and apparatus
65.40.De Thermal expansion; thermomechanical effects

A very simple stabilized single‐mode He–Ne laser for student laboratories and wave meters

B. Ståhlberg, P. Jungner, and T. Fellman

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 878 | Cited 2 times

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The principle and the construction of an intensity and a frequency‐stabilized single‐mode internal mirror He–Ne 633‐nm laser are described. An intensity stability better than 10−3 and a frequency stability better than 10−8 are obtained. The design is very simple, and the system is recommended for student laboratories and for laser‐wavelength meters.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
01.50.Pa Laboratory experiments and apparatus
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Comment on ‘‘Long‐buried dismantling of a centuries‐old myth: Newton’s Principia and inverse‐square orbits,’’ by Robert Weinstock [Am. J. Phys. 57, 846–849 (1989)]

Herman Erlichson

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 882 | Cited 1 time

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Abstract Unavailable
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01.60.+q Biographies, tributes, personal notes, and obituaries
45.05.+x General theory of classical mechanics of discrete systems

A response to Herman Erlichson’s ‘‘Comment on ‘Long‐buried dismantling of a centuries‐old myth: Newton’s Principia and inverse‐square orbits’ ’’ [Am. J. Phys. 58, 882–884 (1990)]

Robert Weinstock

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 884

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Abstract Unavailable
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01.60.+q Biographies, tributes, personal notes, and obituaries
45.05.+x General theory of classical mechanics of discrete systems

A response to Robert H. Romer’s ‘‘Editor’s Note’’ [Am. J. Phys. 58, 882 (1990)]

H. Erlichson

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 886

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Abstract Unavailable
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01.60.+q Biographies, tributes, personal notes, and obituaries
45.05.+x General theory of classical mechanics of discrete systems

Dirac particles in the potential −1/‖x‖

F. Domínguez‐Adame

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 886

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Abstract Unavailable
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03.65.Pm Relativistic wave equations
11.10.St Bound and unstable states; Bethe-Salpeter equations

Rate of rise of liquid in a capillary tube—revisited

Clinton M. Case

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 888

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Abstract Unavailable
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68.03.Cd Surface tension and related phenomena
68.03.-g Gas-liquid and vacuum-liquid interfaces
47.60.-i Flow phenomena in quasi-one-dimensional systems
01.50.Pa Laboratory experiments and apparatus

Why does nothing move faster than light? Because ahead is ahead!

Edwin F. Taylor

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 889

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Abstract Unavailable
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03.30.+p Special relativity

The speed and apparent rest mass of photons in a gravitational field

Renhe Tian and Zhuhuai Li

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 890

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Abstract Unavailable
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03.30.+p Special relativity
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A simple apparatus for observing the Raman effect

Richard Feinberg

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 893 | Cited 2 times

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Abstract Unavailable
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
78.30.C- Liquids
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Einstein and the History of General Relativity

Don Howard, Editor, John Stachel, Editor, and Clifford M. Will

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 894

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Abstract Unavailable
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01.30.Ee Monographs and collections
01.65.+g History of science
04.20.-q Classical general relativity

Neutrino Astrophysics

John N. Bahcall, Author and Ira Wasserman

American Journal of Physics -- September 1990 -- Volume 58, Issue 9, pp. 895

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Abstract Unavailable
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01.30.Ee Monographs and collections
96.60.Jw Solar interior
95.85.Pw γ-ray
95.85.Ry Neutrino, muon, pion, and other elementary particles; cosmic rays
95.30.Cq Elementary particle processes
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