bluuebunny/crossref_metadata_2025 huggingface dataset:
Monitoring Operators in Magnetic Resonance and Light Modulation
Authors: Carver Thomas R. , Partridge Robert B.
Published: August 2005

A density matrix description of magnetic resonance is constructed, with detailed application to spin J = 1 (or greater) particles. Different types of “monitoring” or “measurement” operators employed in atomic beam, induction, and optical experiments are constructed, and used as a compact introductory basis for the description of resonance line shapes and other characteristics of these experiments. Of particular interest are the similarities and unique differences between the optical experiments known by the names “optical pumping,” “double resonance,” and “light beats” on the one hand, and magnetic induction and atomic beam experiments on the other.
Nonholonomic Constraints
Authors: Ray John R.
Published: August 2005

A new method of introducing nonholonomic constraints into the Lagrangian formulation of mechanics is presented and compared with the conventional approach. An example is given using the new formulation. The example falls outside the scope of the conventional approach, but is easily solvable by the new method. Several generalizations of the new method outside the domain of Newtonian mechanics are mentioned.
Physics Curricula and Industrial R & D or the Neglected 42%
Authors: Vollmer James
Published: August 2005

Data in the 1962 National Register of Scientific and Technical Personnel reveal that 42% of all physicists in the United States are employed outside the academic community and do not have Ph.D.'s. When the characteristics and needs of industrial research laboratories are examined against a backdrop of typical physics curricula, serious deviations between the two are discernible. When it is further realized that 46% of all U. S. physicists are working in the classical fields of electronics, electromagnetism, optics, acoustics, fluids, and mechanics, further doubts about course emphasis arise. It is proposed that an academic option be introduced which emphasizes classical physics at an advanced level, while providing a general grasp of the quantum and statistical base. A continuous and unified laboratory program is also recommended. Modifications would extend through the master's degree. The result could be a curriculum capable of efficiently producing the applied physicists which industry clearly needs.
Irreversibility in Simple Systems
Authors: Hobson Arthur
Published: August 2005

In order to illustrate some of the basic principles of statistical mechanics, a study is made of the nonequilibrium behavior of a one-dimensional particle confined to a finite box with perfectly reflecting walls. The statistical aspects of the analysis are due to the incompleteness of the initial information. Liouville's equation is solved exactly and completely, and it is shown that this finite, isolated, reversible system exhibits irreversible statistical behavior. By applying information theory to the results obtained, it is shown that the irreversibility exhibited by this system consists in the information becoming less relevant to the experiments which can be performed on the system.
Maxwell's Ovals and the Refraction of Light
Authors: Sussman Milton H.
Published: August 2005

This paper describes a family of oval curves first studied by Maxwell and which may be called generalized ellipses. Their equation may be written as follows: aS + bS′ = K, where a and b are certain integral values, K any value constant, and S and S′ the distances of a current point from the two foci. The simplest oval results from a = 1, b = 2. Other values of a and b generate similar ovals which are described. If in certain of these ovals the inside and outside regions are filled with material of a definite refractive index, then light proceeding from one focus to the other, will refract stigmatically at the oval surface.
Airy Points of a Meter Bar
Authors: Phelps F. M.
Published: August 2005

If a meter bar of length l and of rectangular cross-section is to be compared with a line standard of typically H cross-section, then it is necessary to support the rectangular bar in such a way that the distance between the engravings will not be altered by deflections due to the weight of the bar. This is achieved by supporting the bar on two half-circular cylinders located at the Airy Points which are, actually, two parallel, symmetrically spaced lines separated by the distance l/3. This problem is both interesting in itself and suitable for use in an undergraduate course in mechanics. It is presented here for its pedagogical value since it is apparently unknown to most professors of physics of the present generation.
More on the Arrow of Time
Authors: Penfield Robert H.
Published: August 2005

A basic time asymmetry is said to exist in the conventional quantum theory of measurement because the initial state, determined by the initial measurement, suffers a reduction of the wave packet when a succeeding measurement is made. It is shown, completely within the conventional framework, that the sense of this time asymmetry can be reversed and a retroductive formalism introduced which is based upon the fact that only the final state is known. Moreover, if both the initial and final states of a set of measurements are fixed, a completely time symmetric formalism can be constructed for the time interval between these given states. The selection of the predictive scheme can be made with the help of macroscopic considerations and consequently it appears that the basic time asymmetry is not a consequence of conventional quantum physics including measurement.
Transformation Properties of the Electromagnetic Field
Authors: Mirman R.
Published: August 2005

The electromagnetic field transforms as an antisymmetric second-rank tensor under Lorentz transformations. Starting with the electric field and relativity, what assumptions are required to obtain this result are considered, as well as how the existence of the magnetic field and some of its properties follow from the transformation law.
Interpretation of Fresnel's Equations for Isotropic Dielectrics
Authors: Rupaal Ajit S.
Published: August 2005

An electromagnetic wave incident on the common surface between two isotropic dielectrics must satisfy Maxwell's boundary conditions at the surface. The existence of these boundary conditions results in a reflected wave and a transmitted wave into the second medium. The ratio of the amplitudes of the electric vectors of the reflected and transmitted waves to that of the incident wave is given by Fresnel's equations. In order to derive these equations from the boundary conditions one generally takes two separate idealized cases. For the first case the electric vector of the incident wave is taken to be perpendicular to the plane of incidence and for the second case the incident vector is considered to lie in the plane of incidence. The general case when the electric vector makes an arbitrary angle with the plane of incidence is then treated by resolving the incident vector into parallel and normal components.
Dynamical Properties of a One-Dimensional “Crystal” with Free Ends
Authors: Clem John R. , Godwin Robert P.
Published: August 2005

Analytical results are provided for the mean-square displacement and velocity of the particles of a simple one-dimensional lattice with free ends in the T = 0°K and high-temperature limits. It is pointed out that care must be used in generalizing from one to three dimensions since the mean-square displacement of a one-dimensional lattice depends on the number of particles. Despite this number dependence the results for the mean-square displacement can be used to show that the effective Debye temperature (as it would be measured by the Mössbauer effect or diffraction experiments) for a central atom is twice that of an end atom, in rough qualitative agreement with detailed three-dimensional calculations. Other effective Debye temperatures are also obtained.
Interferometric Study of the Modes of a Visible-Gas Laser with a Michelson Interferometer
Authors: ten Bosch J. J. , de Voigt M. J. A.
Published: August 2005

A simple Michelson interferometer and a red He-Ne laser were used to measure the visibility of interference fringes as a function of path-length difference of the two beams. The number and intensity of axial modes could thus be determined for various degrees of longitudinal coherence, obtained by deadjustment of the laser-mirror system. The experiment may be used as a student exercise.
Zero-Point Energy and the Lamb Shift
Authors: Power Edwin A.
Published: August 2005

A suggestion by Feynman that the Lamb-shift energy can be obtained from the changes in zero-point energy due to the presence of the atoms involved is worked through in detail for the Bethe nonrelativistic contribution to the energy shift. The self energy of a free electron is obtained in the same way and is equivalent to the state independent shift due to the e2A2/2m2 term in the normal perturbation methods.
Thermocouple Corrections from Irreversibility Theory
Authors: Gaggioli R. A. , Mitchell J. W.
Published: August 2005

The correction for finite impedance of thermocouple instrumentation is derived rigorously from irreversible thermodynamics. Also, the indistinguishability of Peltier and Thomson “emf's” is elucidated.
Torque on a Rigid Body in Circular Orbit
Authors: Mott David L.
Published: August 2005

The torque on a rigid body in circular orbit in a gravitational central field is derived, using the body-centered coordinate system aligned with the gravity gradient vector. Application of the general result to the special cases of pure pitch, roll, and yaw rotations is considered. From these cases, the orientations of stable equilibrium are deduced.
The Relativistic Rocket
Authors: Pomeranz Kalman B.
Published: August 2005

The equation of motion for a relativistic rocket or for any particle with a variable rest mass may be derived by applying the relativistic impulse-momentum and work-energy principles in the instantaneous rest frame. The equation of motion in this frame is in the classical non-relativistic form. The equation of motion in the observer's rest frame may then be deduced by applying the relativistic transformation equations for velocity, force, and time.
Force-Free Magnetic-Field Problem
Authors: Freire Gabriel F.
Published: August 2005

A brief discussion is given of force-free magnetic fields generated by two systems of mutually orthogonal currents in a homogeneous and unbounded conducting fluid. Rectangular, cylindrical, and spherical force-free field solutions are presented as examples illustrating the problem.
Apparatus for Teaching and Research in Electron Physics
Authors: Kendall B. R. F. , Luther H. M.
Published: August 2005

A special form of construction for electron devices is described. This construction makes it possible to assemble a wide range of apparatus from inexpensive standard parts, without the use of tools. Modifications can be made with particular ease because the electrodes can be installed, repositioned or removed independently of one another. These features make the apparatus convenient for use in undergraduate and graduate laboratory projects, as well as in more advanced research applications. Examples are given of some typical assemblies, ranging from simple electron emitters to cathode-ray tubes, electron multipliers, and a complete mass spectrometer.
Operator Gauge Transformations and Gauge Transformations of the Third Kind
Authors: Gaisser T. K.
Published: August 2005

A connection between gauge transformations of the third kind and operator gauge transformations of the first and second kinds is shown to hold for the electron propagator and for the vertex function of quantum electrodynamics as well as for the photon propagator. A method for calculating the gauge change of any time ordered n-point function is indicated.
Guided Surface Waves and the Radiation from Charges Moving in Curved Paths
Authors: Lawson J. D.
Published: August 2005

The main purpose of the paper is to illustrate the analogy between the radiation from a guiding surface which is bent or curved, and the radiation from an electron which is deflected (brems-strahlung) or moves in a curved path in a magnetic field (synchrotron radiation). In developing this analogy the significance of the “characteristic radius” associated with a cylindrical or spherical wave system, defined as the radius at which the argument of the radial wavefunction is equal to its order, is examined. A small diversion is made to illustrate the relevance of this concept to atomic radiation, supergain antennas, and wave-mechanical scattering.
Angular Distribution of the Acoustic Radiation from a Tuning Fork
Authors: Sillitto R. M.
Published: August 2005

It is shown by elementary arguments that the familiar loudness distribution pattern in the immediate neighborhood of a tuning fork is not, as is often suggested in elementary texts, due to pathlength-dependent phase differences between the waves reaching the ear from the different faces of the prongs, but to pathlength-dependent amplitude differences. At great distances from the fork, however, amplitude variations become negligible and pathlength-dependent phase differences give rise to a quite different loudness distribution pattern. From an idealized model, which represents a tuning fork as four colinear sources of strengths +B, −B, −B, +B, the velocity potential is calculated and the mean-square-pressure and intensity distributions are derived. It is shown that the mean-square-pressure distribution depends on polar angle (θ) and distance (R) as (3 cos2θ − 1)2/R6 close to the fork—the easily audible (amplitude-dependent) nearfield pattern; and as cos4θ/R2 at great distances—the less familiar (phase-dependent) farfield case. The intensity distribution comprises a cos4θ/R2 radial outward flow with, superposed, a circulation of energy from equatorial (θ ≈ 90°) to polar (θ ≈ 0,thinsp;180°) regions, varying with distance as 1/R4. There are two zeroes of intensity: where R = 0.225λ, θ = 0 and 180°. The power radiated is estimated for a typical 520 cps fork, and is found to be 2.5 × 10−15 W when the prongs vibrate with an amplitude of 0.2 mm.
Demonstrations of Fluid Flow in a Rotating System
Authors: Baker D. James
Published: August 2005

The importance of rotational constraints on fluid flow in geophysical and astrophysical problems suggests that demonstrations of these constraints would be useful in undergraduate physics courses. A theoretical derivation of some rotational effects is presented, together with the complete details of four lecture demonstrations which exhibit these effects.
Quantum Mechanics as a Model
Authors: Buch Tomas
Published: August 2005

The shock to which students approaching quantum mechanics for the first time are exposed by the introduction of the postulates on which the mathematical framework of the theory is based, can be much smoothed by a discussion of a semiphilosophical nature about the connection between mathematical theories and the physical reality they are supposed to explain. The general outline of such a discussion is presented, with the purpose of making the introduction of operators to represent physical magnitudes more plausible to the students.
Quantitative Demonstration Exhibits and a New Low-Cost Physics Laboratory
Authors: White Harvey E. , Weltin Hans , Gould Mauri , Rice Robert A.
Published: August 2005

A number of self-instruction demonstration exhibits with quantitative capabilities have been constructed over the past four years at the Lawrence Hall of Science. Many of them have been exhibited in the laboratories and corridors of local high schools, in the Fleischmann Atmospherium at the University of Nevada, and in a temporary exhibit hall on the University of California campus in Berkeley. A pilot laboratory program is now being conducted with 500 students in the Physics Department. Eleven of the self-instruction exhibit experiments have been set up in a room where students make observations and record data. It is now estimated that this kind of laboratory operation, properly set up, will cost less than twenty per cent of the generally accepted college or high-school laboratory operations, and that forty experiments per year student can readily be performed instead of twenty. These laboratory practices are more effective than lecture demonstrations and are infinitely better than no laboratory at all.
Modified Form of Carathéodory's Second Axiom
Authors: Sears Francis W.
Published: August 2005

A modified form of Carathéodory's Axiom II is proposed. Like Axiom I it is phrased in terms of the work in adiabatic processes and, together with Axiom I, it leads directly to the existence of reversible adiabatic surfaces and hence to the concepts of entropy and absolute temperature. The original Axiom II is shown to be a consequence of the proposed axiom. The multiplicity of possibilities that is characteristic of conclusions based on the original Axiom II is eliminated.
A Note on Hertz's “Derivation” of Maxwell's Equations
Authors: Havas Peter
Published: August 2005

In a recent article, Zatzkis has drawn attention to Hertz's “derivation” of Maxwell's equations from an earlier action-at-a-distance theory. Hertz's procedure leads to an infinite series for the potentials which satisfies Maxwell's equations. It is demonstrated that for a current distribution which is an analytic function of the time this series is the Lagrange expansion of the half-retarded, half-advanced solution of Maxwell's equations; for general source functions the series has no physical meaning. Thus Hertz's procedure does not yield the full Maxwell theory and, in particular, can not account for radiation. It is then shown that, contrary to Zatzkis's contention, in the illustrative example treated by Hertz the original solution is mathematically correct; however, it is physically inadequate.
Transformation of Operators
Authors: Cohen Leon
Published: August 2005

A method is given for the transformation of operators from one representation to another. Explicit expressions are derived. The transformation to complex valued representation is also considered.
Are Zero Rest Mass Particles Necessarily Stable?
Authors: Havas Peter
Published: August 2005

Various authors have stated recently that particles of zero rest mass are necessarily stable as a consequence of known conservation laws or of requirements of relativistic invariance. It is shown that such a conclusion is not warranted. A proper relativistic characterization of unstable particles of zero rest mass is given, and examples of decay schemes of the photon and the neutrino not forbidden by general considerations are indicated. The questions of experimental evidence and detection of photon decay are briefly discussed. In an Appendix, the problem whether photon decay is allowed by quantum electrodynamics is outlined; no definite conclusions can be drawn from available calculations.
Spin Without Commutation Rules
Authors: Epstein Saul T.
Published: August 2005

The Pauli spin matrices are derived in a way which makes no appeal to the usual apparatus of abstract operators, commutation rules, etc.
Angular Momentum of Static Electromagnetic Fields
Authors: Romer R. H.
Published: August 2005

A recently described “paradox” in classical electromagnetic theory is resolved by recognizing the fact that even a static electromagnetic field may have angular momentum. A charged particle, emitted from a source in a magnetic field, acquires a readily calculable angular momentum under the influence of the Lorentz force. The angular momentum of the static field after the emission of the particle can be independently calculated, and differs from its previous value by an amount which is exactly the negative of the angular momentum acquired by the particle. If the magnetic field is subsequently turned off, the field angular momentum which disappears is found to be exactly accounted for by changes in mechanical angular momenta. These results, although hardly surprising, provide a very clear illustration of the reality of field angular momentum, especially since the geometry is so simple that exact calculations can readily be made.
An Anschaulichkeitsbeweis for Special Relativity
Authors: Goe George
Published: August 2005

Using imagery like Poincaré's for the hyperbolic world, the geochronometry of special relativity is shown to be derivable from the assumption that rods and clocks in uniform motion with respect to one particular inertial frame of reference are subject to contraction and retardation, respectively, in accordance with the relativistic formula. If the invariance of all physical laws under the Lorentz transformations, which express that geochronometry, is then postulated, the special theory of relativity follows in its entirety.
To Scatter a Photon by a Photon
Authors: Rosen Gerald
Published: August 2005

This paper gives a more detailed description of the “x-ray-flashbulb” experiment for observing the scattering of light by light in vacuum. It is shown here that at least ten to twenty scattering events can be initiated by two x-ray flashbulbs, properly oriented and synchronized to flash together in an appropriate experimental arrangement.
Simplified Derivation of Bogoliubov's Generalized Boltzmann Equation
Authors: Bober William
Published: August 2005

The derivation of the generalized Boltzmann equation is presented from a more elementary viewpoint than that given by Bogoliubov and others working in the field of kinetic theory of gases. Like the other derivations, the starting point is the Bogoliubov, Born, Green, Kirkwood, and Yvon (B-B-G-K-Y) hierarchy equations. However, no formal attempt is made to obtain corrections to account for three or more body collisions. Furthermore, there is no a priori assumption made that the lower-order distribution functions Fs(s≥2) are functions of time through the one-particle distribution function F1.
A Macroscopic Approach to Ohm's Law
Authors: Podolsky Boris , Denman Harry H.
Published: August 2005

Although a proper derivation of Ohm's law for a particular material should be based on a quantum mechanical treatment of that material, it is interesting to see how far one can proceed on a purely macroscopic basis. It is shown here that for homogeneous, isotropic materials, one can expect an odd voltage-current relation, and that ordinarily Ohm's law will be obeyed as accurately as one wishes over some range of voltage and current. Only the ideas of causality, symmetry, and analyticity are used. Further, if Ohm's law is followed exactly by a material at constant temperature but the resistance is a function of the temperature, and the departure from Ohm's law is due entirely to Joule heating, then it is shown that the odd voltage-current relation still obtains.
Dialogues Concerning Some Old Sciences—The Seattle Interdisciplinary Conference
Authors: Jossem E. Leonard
Published: August 2005

A conference to identify specific problems in areas which are of interest in instruction at the undergraduate level in two or more disciplines was held at Seattle in June 1965. The meetings were organized jointly by the commissions on college physics, chemistry, and biology and were attended by representatives of the college commissions on geology, geography, engineering, agriculture, and mathematics. The work of the conference was carried out by four subgroups which were charged with the investigation of interdisciplinary problems and opportunities in the following areas: (1) The biology-chemistry interface; molecular structure; (2) The chemistry-physics interface, macroscopic and statistical thermodynamics; (3) Quantum mechanics; (4) Interdisciplinary experimental science. Each of the groups made recommendations for future efforts in the area with which it was concerned. Ways of implementing these recommendations are under consideration by the relevant commissions.
PSNS Project at RPI
Authors: Wood Elizabeth A.
Published: August 2005

During 1963 and 1964 the Commission on College Physics and the Advisory Council on College Chemistry sponsored a series of conferences whose purpose was the stimulation of projects to design new courses in physical science for nonscience majors. As an outgrowth of these conferences the Physical Science for Nonscience Students Project was begun in April of 1965 at Rensselaer Polytechnic Institute, Troy, New York, under a grant from the National Science Foundation. The Project Director is Professor Lewis G. Bassett of the Chemistry Department of RPI. Dr. Elizabeth A. Wood of the Physical Research Department of Bell Telephone Laboratories is Associate Director and Chairman of the Advisory Board, and Professor Robert L. Sells of the Physics Department of the State University College of New York at Geneseo also serves as Associate Director. Further information on the PSNS Project, including a table of contents of the text as it presently stands, an excerpt from the text, and a list of participants, is contained in the PSNS Newsletter #1 which is available from the Project Director.
Inverse Velocity Space Spectra and Kinetic Equations
Authors: Diament Paul
Published: August 2005

Transformations of velocity distribution functions to “inverse velocity space” are shown to provide alternative, and often preferable, statistical descriptions of collections of particles. The salient properties of these Fourier-transformed distributions are outlined and their utility and advantages illustrated through applications in plasma theory. The corresponding transformations of the Boltzmann and other kinetic equations are presented, together with those of several collision models. A table of inverse velocity spectra for various velocity distributions is provided for reference.
Laboratory Demonstrations in Mechanics using Electrical Readout
Authors: Ruby R. H.
Published: August 2005

A brief description of several mechanics experiments combining the apparatus of the Berkeley Physics Laboratory with mechanical systems. Experiments described are the measurement of g and harmonic oscillators.
Coupled Oscillators and Normal Coordinates
Authors: Chen Henry S. C.
Published: August 2005

Two blocks and three heavy springs are coupled together and made to oscillate on an air track. The motion of one of the blocks is recorded by means of a spark timer. With arbitrary initial conditions, the motion is complicated. From the masses of the blocks and the springs and from the spring constants, one then calculates theoretically the normal coordinates. These normal coordinates are then excited, one at a time. The results are two harmonic curves. Agreement between the experimental and the calculated values of the normal frequencies is excellent.
Conversion of a Grid-Dip Meter into a Variable Frequency NMR Spectrometer
Authors: Rubinstein M. , Shtrikman S.
Published: August 2005

A variable-frequency NMR spectrometer, constructed from a commercial grid dip meter, is described. The spectrometer is exceedingly simple to construct. It may be operated in either the marginal or the super-regenerative mode. Although applications to magnetically ordered materials are stressed, the spectrometer can be used to detect nuclear magnetic and nuclear quadrupole resonances in nonmagnetic substances as well.
Derivation of the Equations of Motion of a Classical Radiating Charge
Authors: Cohn Jack
Published: August 2005

The present paper is concerned with a derivation of the equations of motion of a classical radiating charge. Although heuristic assumptions are involved in the treatment, there is compensation from the fact that the derivation involves much less mathematical complexity than is found in the customary treatments of the problem. The formulation is manifestly covariant throughout.
Small Oscillations of a Stabilized, Inverted Pendulum
Authors: Ness Douglas J.
Published: August 2005

The author describes a physical pendulum designed to reduce significantly friction and flexure at its point of suspension. Theoretical results concerning the basic period for motions of the pendulum in the neighborhood of the stabilized upward position are experimentally confirmed, as are theoretical results concerning the stability boundary of such motions.
Stereographic Projections of the Colored Crystallographic Point Groups
Authors: McMillan J. A.
Published: August 2005

Consideration of a double-valued attribute affecting spatially equivalent points in the crystallographic point groups leads to Shubnikov's colored point groups, after a nonspatial operator of order two is introduced to restore the symmetry. The stereographic projections of the 90 Shubnikov point groups are presented. The analogies among scalar, polar- and axial-vector attributes are considered. Identification of the nonspatial operator as time reversal in magnetic configurations and some instructional examples are discussed.
One-Dimensional Wave Demonstration
Authors: Fowler John M. , Brooks John T. , Lambe Edward D.
Published: August 2005

A model of a simple one-dimensional medium has been developed which allows most of the important features of traveling waves to be quantitatively demonstrated. Air-suspended disks are connected by light springs and the resulting “lumped-parameter” line is easily analyzed. Phase and group velocity, dispersion, the cutoff frequency, and other more subtle features of wave motion can be computed and measured in class. The device is also useful for studying standing waves.
Precision Measurement of the Period of a Pendulum Using an Oscilloscope
Authors: Li Seung-ping , Feng Shih-yu
Published: August 2005

The period of a simple pendulum was measured with a precise timing system consisting of a phototransistor, the output of which triggered the sweep of an oscilloscope which, at the same time, displayed the standard radio time signal of JJY from Tokyo, Japan. The oscilloscope display was photographed with a Polaroid camera and the period was calculated. The method is simple, does not require elaborate pieces of equipment, and still gives accuracy to ± 4 parts in 106.
Construction and Operation of a Small Electrostatic Accelerator for an Undergraduate Laboratory Course
Authors: Post Richard S. , Mark Hans
Published: August 2005

This paper describes the construction and operation of a small electrostatic accelerator. The machine was built by undergraduate students in an Engineering Science Laboratory Course for seniors. The purpose of this paper is to describe some of the features of the machine with particular emphasis on construction techniques. The machine was built with surplus or salvaged equipment at a total cost of about $800.00. Several experiments which can be performed with the machine will be described.
Resource Letter NPE-1 on Nuclear Photographic Emulsions
Authors: Friedlander M. W.
Published: August 2005

Prepared at the request of the AAPT Committee on Resource Letters; supported by a grant from the National Science Foundation.

This is one of a series of Resource Letters on different topics, intended to guide college physicists to some of the literature and other teaching aids that may help them to improve course contents in specified fields of physics. No Resource Letter is meant to be exhaustive and complete; in time there may be more than one letter on some of the main subjects of interest. Comments and suggestions concerning the content and arrangement of letters as well as suggestions for future topics will be welcomed. Please send such communications to Professor Joel E. Gordon, Resource Letter Committee, Department of Physics, Amherst College, Amherst, Massachusetts 01002.

Notation: The letter E after an item number indicates elementary level, useful principally for high school and introductory college use; the letter I indicates intermediate (junior, senior) level; and the letter A indicates advanced material, principally suited for senior, graduate study. An asterisk (*) indicates items particularly recommended for introductory study.

Additional copies: Available from American Institute of Physics, 335 East 45 Street, New York, New York 10017. When ordering, request Resource Letter NPE-1 and enclose a stamped return envelope.
Infinitesimal Lorentz Transformations—Spinorial Representations
Authors: Strecker Joseph L.
Published: August 2005

By considering directly an infinitesimal transformation to a moving frame, the generators of the spinorial representation of the Lorentz group are obtained.
The Calorator: A Simple Heat Engine with Which the Motion of Individual Molecules may be Demonstrated
Authors: Kenty Carl
Published: August 2005

In any heat engine heat is taken in by the working substance from a hot body and some of it is given up to a cold body; meanwhile the difference, limited in amount, is converted into useful work. The device here to be described accomplishes this function in an extremely simple manner. Continuous rotation of a system of vanes is caused by the single impacts of molecules. The device may therefore be said to operate be radiometer action. A disk twisted with tweezers to resemble the blades of an electric fan is mounted on a fine needle with sharpened and polished ends. The disk and its shaft are mounted between pivot bearings on a light wire frame which slip into a glass bulb which is then filled with 20-mTorr helium. If the bulb is now held in the hand either above or below the disk, the disk will turn at a speed of several rps due to the warmth of the hand. The cooling effect of a wet string tied around the bulb, either above or below the disk, will also turn it very nicely. The device, hung by a very fine wire, serves as a simple Knudsen-type pressure gauge. By contacting the bulb either just above or just below the disk with a string dipped in water, the device operates as a relative-humidity indicator. It has also been made to indicate whether the temperature is rising or falling and at what rate.
Lorentz Contraction
Authors: Marx Egon
Published: August 2005

We examine two thought experiments in order to determine under what circumstances the Lorentz contraction in the special theory of relativity allows a moving rod to pass through a slit in a wall parallel to it when the length of the slit is smaller than the uncontracted length of the rod. We conclude that the outcome of such an experiment depends critically on the definition of parallelism.
Infinitesimal Lorentz Transformation
Authors: Strecker Joseph L.
Published: August 2005

By means of a series of arguments, a general Lorentz transformation is derived in the infinitesimal. This gives the generators of the group, and exponentiation produces a finite transformation.
Improved Sophomore Experiment to Measure Latent Heat of Fusion
Authors: Soules Jack A.
Published: August 2005

Ice is melted by electrical heat supplied to a constant-temperature calorimeter. The amount of ice melted is obtained by observing the change in volume of the system at constant pressure. The determination of the latent heat is precise to within ±1%. In a less precise variation, supercooled water is allowed to freeze and the latent heat is determined from the expansion of the system and the amount of warming which occurs. Students react to the phenomenon with surprise; although the precision is poor, the supercooling experiment is a very effective teaching device.
Optical Absorption in a Kronig-Penney Semiconductor
Authors: Wilsey Neal D. , Goodman R. R.
Published: August 2005

The Kronig-Penney model for the electron potential in a crystal is discussed for a simple cubic lattice. The model is adapted to a semiconductor, and it is shown that quantities such as effective mass and optical absorption coefficients near the absorption edge may be calculated.
How Determinate is the “Billiard Ball Universe”?
Authors: Raymond D. J.
Published: August 2005

It is generally supposed that distinctly quantum-mechanical effects do not show up on the macroscopic level. However, it is shown here that the uncertainty principle imposes a drastic limit on the predictability of the detailed motion of a collection of colliding hard spheres, or “billiard balls.”
Laboratory Notebooks of G. S. Ohm: A Case Study in Experimental Method
Authors: McKnight John L.
Published: August 2005

The attempt to set out an exact codification of “scientific method” would result in a vast over-simplification of the practice of science. G. S. Ohm's laboratory notebooks of 1825 and 1826, in which he records his experiments on current electricity in resistive circuits, afford an excellent example of the procedure of science with its interplay of theory and experiment. In them, improvements in procedure and in apparatus parallel and complement advances in the theory.
Debye Shielding and Virtual Plasma Oscillations
Authors: Schulz Michael
Published: August 2005

It is noted that Debye shielding between charges in a one-fluid plasma, and under certain conditions in a two-fluid plasma, can be represented formally by coupling the charges to a field of isothermal plasma oscillations. The field-theoretic calculation required in such a model would be equivalent mathematically to the coupling of point sources to a field having quanta of nonzero mass, and so the resulting potentials would have the same form, as is known to be the case in the usual thermodynamic model for Debye shielding.
Diffraction of Spark-Produced Acoustic Impulses
Authors: Wright Wayne M. , McKittrick James L.
Published: August 2005

A transient electrical discharge in air serves as a convenient source of acoustic impulses for studies of wave diffraction. “N waves,” with initial shocks about 0.01 atm in magnitude and with durations of less than 30 μsec at 10 cm distance, are produced by sparks having discharge energies of 0.05 J. They are detected with wide-band condenser microphones, which utilize a 14-mil metallized Mylar diaphragm supported partially by the thin layer of air trapped on a machined brass surface. The receiving response is nominally flat to above 12 MHz. Phenomena which are demonstrated here include the diffraction of N waves incident upon circular disks and narrow rectangular plates.
Waveguide Analog of Tunneling through Quantum Potential Barriers
Authors: Campi Morris , Harrison Mark
Published: August 2005

Expressions are derived for the electromagnetic fields of guided waves which are analogous to the quantum-mechanical equations representing barrier tunneling. This analogy is achieved by comparing the propagation constant of the Schrödinger time-independent wave equation with that of the electromagnetic wave equation in waveguide and by comparing the de Broglie wavelength of a particle with the wavelength of the waves that propagate the energy. This results in an expression relating the form of an arbitrary one-dimensional energy barrier to the physical dimensions of a section of waveguide. The analogy is tested by the propagation of energy in the TE10 mode at both the 3- and 6-cm bands for the cases of rectangular and hyperbolic barriers. Although evanescent modes are present at the discontinuous regions, the analog for the rectangular barrier, which is considered to be the worse case, is verified when an effective barrier length leff of about 1.2l is used. This experimental verification demonstrates the possibility of waveguide simulation of quantum-mechanical energy barriers and the practicality of utilizing an electromagnetic analog for demonstrating the tunneling phenomenon and provides a method for measurement of the transmission coefficient through an arbitrarily shaped barrier.
Physical Significance of the Poynting Vector in Static Fields
Authors: Pugh Emerson M. , Pugh George E.
Published: August 2005

Even in static fields, where there is no observable energy flow, Poynting vector momentum must be considered to avoid an apparent violation of the angular-momentum law. This often-neglected aspect of the Poynting vector, is illustrated in an easily calculated example. Two other simple and rigorously solvable pedagogical examples illustrate the role of the Poynting vector in defining the energy flow in static fields.
Resource Letter ColR-1 on Collateral Reading for Physics Courses
Authors: Bork Alfred M. , Arons Arnold B.
Published: August 2005

Prepared at the request of the AAPT Committee on Resource Letters; supported by a grant from the National Science Foundation.

This is one of a series of Resource Letters on different topics, intended to guide college physicists to some of the literature and other teaching aids that may help them improve course content in specified fields of physics. No Resource Letter is meant to be exhaustive and complete; in time there may be more than one letter on some of the main subjects of interest. Comments and suggestions concerning the content and arrangement of the letters as well as suggestions for future topics will be welcomed. Please send such communications to Professor Joel E. Gordon, Chairman, Resource Letter Committee, Department of Physics, Amherst College, Amherst, Massachusetts.

Additional copies: Available from American Institute of Physics, 335 East 45 Street, New York, New York 10017. When ordering, request Resource Letter ColR-1, and enclose a stamped return envelope.
Computer-Generated Motion Pictures of One-Dimensional Quantum-Mechanical Transmission and Reflection Phenomena
Authors: Goldberg Abraham , Schey Harry M. , Schwartz Judah L.
Published: August 2005

We describe the details involved in presenting the time development of one-dimensional quantum-mechanical systems in the form of computer-generated motion pictures intended for pedagogic purposes. Concentrating on reflection-transmission phenomena, we formulate the problem in terms of a Gaussian wave packet impinging on a square well or barrier and being reflected and transmitted. The wave equation is solved numerically by methods discussed in detail and photographs of the wave packet vs position at a variety of times and for a range of projectile energies are given.
Invariant Velocity Components: A Key to Newton's Analysis of Keplerian Planetary Motion
Authors: Cronin James L. , Jones Leonard C.
Published: August 2005

A graphical model of Keplerian planetary motion is used to deduce the inverse-square law of force. Invariant velocity components are utilized that reflect the geometric properties of the elliptic planetary orbit and the geometric characteristics of the vector quantities, force, and linear momentum.
Derivation of the Spin-Orbit Interaction
Authors: Farago P. S.
Published: August 2005

Many students find it paradoxical that spin-orbit coupling is discussed in nonrelativistic quantum mechanics although it is usually said to be a consequence of relativity. The resolution of this paradox is discussed. The Thomas precession is related to the commutation properties of the matrices used to describe the resultant of two consecutive Lorentz transformations without rotation; the frequency of the Thomas precession is derived on this basis.
Invariance Principles in Classical and Quantum Mechanics
Authors: Chern Bernard , Tubis Arnold
Published: August 2005

A simple, unified discussion of invariance principles in nonrelativistic classical and quantum mechanics is presented. In particular, space-translation, space-rotation, space-inversion, Galilean, and time-reversal invariance are discussed from the point of view of possible physical motions. In addition, there is a discussion of the classical connection between space inversion, time reversal, and what may be considered a type of “charge conjugation.”
Resource Letter LH-1 on Liquid Helium
Authors: Lane C. T.
Published: August 2005

Prepared at the request of the AAPT Committee on Resource Letters; supported by a grant from the National Science Foundation.

This is one of a series of Resource Letters on different topics, intended to guide college physicists to some of the literature and other teaching aids that may help them improve course contents in specified fields of physics. No Resource Letter is meant to be exhaustive and complete; in time there may be more than one letter on some of the main subjects of interest. Comments and suggestions concerning the content and arrangement of letters as well as suggestions for future topics will be welcomed. Please send such communications to Professor Joel Gordon, Chairman, Resource Letter Committee, Department of Physics, Amherst College, Amherst, Massachusetts.

Notation: The letter E after the item number means that the reference should be mainly useful for elementary courses. In view of the complexity of the subject elementary will normally imply junior courses. The letter I indicates intermediate (senior and first-year graduates) and A indicates advanced (second-year graduates and students beginning research in Physics). An asterisk indicates items particularly recommended for introductory study.

Additional copies: Available from American Institute of Physics, 335 East 45 Street, New York, New York 10017. When ordering, request Resource Letter LH-1 and enclose a stamped return envelope.
On Classification of Curvature Tensor
Authors: Misra R. M.
Published: August 2005

A new method for classification of the gravitational field is presented. It is shown that this scheme leads to exactly the same types of gravitational fields as previously obtained by Petrov, Penrose, and Sachs, etc. Some physical applications are also given.
Wave Patterns in Dispersive Media
Authors: Breeding J. Ernest
Published: August 2005

A comparison is made between wave patterns in dispersive and nondispersive media on the basis of the interference patterns of two sine waves. The sine waves are assumed to be of equal amplitude and to have a common direction of propagation. For the dispersive medium, it is shown that the wave pattern observed as time varies at a given position is not the same as that found when considered as position changes for an instant of time. For corresponding intervals of space and time it is found that the snapshot contains a different number of individual oscillations than the sample at a single location. The difference is seen to increase as the component frequencies become more nearly the same.
Double Layers and Solid Angle in Potential Theory
Authors: Djurić Jovan
Published: August 2005

The paper discusses the erroneous interpretation of the double layer as a source of a presumed nonconservative field, and traces back that very old mistake to works of Ampere, Gauss, and Maxwell. That mistake is repeated by all authors up to the present time. It is shown that the magnetic double layer creates a strictly conservative field, which is not completely equivalent to the field of a filamentary current loop, since that field is nonconservative. It is further shown that the solid angle is a single-valued function with the step discontinuity, and by no means a multiple-valued function.
Strain-Gauge Transducer for Fluctuating Pressure Study
Authors: Gill B. S. , Modi V. J. , Tong K. L.
Published: August 2005

A strain-gauge transducer suitable for measuring acoustic-level pressure fluctuations is described here. The wind tunnel determination of Strouhal number and fluctuating-pressure coefficients associated with a circular cylinder due to shedding vortices showed satisfactory agreement. The simple and inexpensive transducer has proved useful in the aeroelastic instability study of bluff cylinders.
Normal Shock Waves in a Compressible Fluid
Authors: Blum Ronald
Published: August 2005

The fundamental principles and relations governing normal shock waves in a compressible fluid, in both the classical and hydromagnetic cases, are stated and derived in a manner suitable for inclusion in an undergraduate physics curriculum. Acoustic and magnetoacoustic velocities are derived as limiting cases of very weak shocks, and the second law of thermodynamics is employed to demonstrate that fluid flow through a stationary shock wave always requires a supersonic-to-subsonic transition.
Finite Speed of Propagation in Heat Conduction, Diffusion, and Viscous Shear Motion
Authors: Weymann Helmut D.
Published: August 2005

It is shown that the apparent infinite propagation velocity in heat conduction is the result of neglecting the atomistic structure of matter. A modified differential equation is derived which gives a finite speed of propagation.