Volume 45, Issue 7, July 1977
 Awards


Response of the Oersted Medalist
View Description Hide DescriptionE d i t o r’s n o t e: Remarks made by H. Richard Crane upon receipt of the 1976 Oersted Medal. Bestowed by the American Association of Physics Teachers ’’for notable contributions to physics education,’’ the Medal was presented to Professor Crane at the ceremonial session of the joint meeting of the American Physical Society and the American Association of Physics Teachers, Chicago, Illinois, 7–10 February 1977. [See J. B. Guernsey, Am. J. Phys. 45, 507 (1977), for remarks made in presenting the Medal.]
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 Papers


Laboratory experiments with silicon solar cells
View Description Hide DescriptionThe uses of silicon solar cells as subjects of experiments in undergraduate teaching laboratories are discussed. The basic theory of these cells is presented, including equivalent circuits and characteristic equations. Fundamental experiments on the power output and efficiency, which are appropriate for non‐science majors’ courses, are detailed, as well as more advanced experiments on cell parameters. Experimental results and agreement with theory are presented for a typical inexpensive cell.

Projectile motion with air resistance quadratic in the speed
View Description Hide DescriptionWe consider two‐dimensional motion of a projectile experiencing a constant gravitational force and a fluid drag force which is quadratic in the projectile’s speed. The equations of motions are coupled nonlinear equations. Their solutions have general properties which are easily visualized, although much different from those obtained when a drag force is neglected. Because of these features a study of these equations would provide an interesting counterpoint to the already familiar case of no drag. In this paper we derive simple approximate solutions to the equations of motion for both short and long times. A numerical example is used to compare these approximate solutions with accurate results obtained by numerical integration from an exact but implicit solution. Finally, the origin of the quadratic drag force is discussed.

Two Van de Graaff experiments for the senior laboratory
View Description Hide DescriptionTwo experiments in nuclear physics for a senior level laboratory course are described. One experiment is a measurement of resonances in a nuclear reaction. Simple electronics, a NaI detector, a system for evaporating thin layers of material onto a metal backing in vacuum, and a method of measuring the magnetic field in the Van de Graaff analyzingmagnet are needed. The other experiment is a measurement of the p+p elastic scattering cross section at a laboratory angle of 45° and at bombarding energies near 400 keV. The interference between Coulomb and nuclear scattering is studied. Two surface barrier detectors, standard coincidence electronics, and a windowless gas target are used.

Nonrelativistic quantum mechanics and the anomalous part of the electron g factor
View Description Hide DescriptionThe departure of the electron g factor from 2 is calculated using a nonrelativistic theory of the electron interacting with the quantized transverse electromagnetic field. Although the magnetic moment correction δμ, due to the radiation field, is antiparallel to the magnetic moment μ_{0} of the bare electron, it is shown that the g factor correction is positive for a reasonable cutoff. This is due to the fact that the g factor is defined as the magnetic moment in units of the ’’physical’’ Bohr magneton. The role of mass renormalization is emphasized in this approach, and it is shown that the experimental g factor emerges for a cutoff of 0.53 electron masses.

Application of the Dirac delta function to electric charge and multipole distributions
View Description Hide DescriptionWe introduce the concept of equivalent volume charge density for all types of charge and multipole distributions, discrete as well as continuous. The equivalent volume charge density for point charges, point dipoles, and point quadrupoles is expressed in terms of the Dirac delta function and its derivatives. The equivalent volume charge density for surface charge distributions and surface dipole distributions is obtained by introducing a ’’surface delta function.’’ The well‐known equivalence between a continuous distribution of dipoles within a specified volume and the volume and surface densities is derived directly by means of the delta function formalism. The same method is also applied to find the equivalent volume and charge distributions for a continuous distribution of quadrupoles confined in a specified volume.

Investigating the physical nature of the Coriolis effects in the fixed frame
View Description Hide DescriptionIt is shown that investigating Coriolis effects in the fixed frame leads to a clearer understanding of their physical nature: the body carries along its initial velocity, larger or smaller than the velocity of its corresponding point during the motion. A simple but thorough calculation of some effects (the Foucault pendulum and the eastward drift of a falling body) is given.

Simple geometrical means of visualizing families of Rayleigh hysteresis loops
View Description Hide DescriptionA simple geometrical means of visualizing and generating families of Rayleigh magnetic hysteresis loops is presented.

Quantitative angular momentum experiment on the rotating chair
View Description Hide DescriptionThe popular rotating chair and hand‐held weights demonstration on the conservation of angular momentum has been adapted to the lower division laboratory. The demonstration has been made quantitative by adding radial tracks to the chair along which calibrated masses may be positioned without extension of the occupant’s arms. The conservation of angular momentum can be tested and the moment of inertia of the student in various sitting positions can be determined.

Polarization characteristics of scattered light
View Description Hide DescriptionAn undergraduate experiment investigating the polarizationcharacteristics of light scattered from a dielectric cylinder is presented. Students generally find the results surprising; however, the observations support the predictions of classical electromagnetic theory.

Properties of an infinite linear array of atoms based on a Morse pairwise potential
View Description Hide DescriptionProperties of an infinitely long, linear array of atoms are described assuming the atoms interact with each other via a Morse pairwise potential. The equilibrium lattice parameter for a regularly spaced array is calculated, as is the potential function pertinent to vacancy migration. A specific numerical example is considered using the Girifalco and Weizer parameters for the pairwise interatomic potential characterizing body‐centered‐cubic iron.

Generalized Doppler formula in a nonstatic universe
View Description Hide DescriptionThe general Doppler formula in a nonstatic universe is derived, relating the expansion of the universe and the peculiar velocity of the light‐emitting object to the shift of spectral lines measured by a fundamental observer. No reference to the Riemannian metric of general relativity is required; the only assumptions needed are special relativity, homogeneity, and isotropy of the universe. A few examples of applications to physical cosmology are given.

Paradox and resolution in electrostatics
View Description Hide DescriptionA closed conducting surface possessing both conduction electrons and muons is hypothesized. A simple and persuasive proof is given, entirely in the framework of classical electrostatics and Newtonian gravity, to show that the region interior to such a surface is shielded from gravity. The resolution of the paradox is explained and a solution is given for the gravitational and electrostatic forces inside a spherical surface of the type hypothesized.

Results of a remedial laboratory program based on a Piaget model for engineering and science freshmen
View Description Hide DescriptionEngineering and science freshmen who enter our institution with algebra deficiencies have a very low probability of performing satisfactorily in the required college‐level calculus course. Two years ago, a remedial one‐semester program was conducted for 36 freshmen who were identified by an entrance examination as being weak in algebra. The course was based on the assumption that the students were ’’concrete’’ in the Piagetian sense. The main part of the course required a general physics laboratory that provided selected experiences to bridge the concrete–formal gap. After three semesters, 31% of the participants in the course were receiving grades of C or above in calculus courses, as compared to 16% of those students who did not take the remedial program.

Transformation theory, accelerating frames, and two simple problems
View Description Hide DescriptionAn operator which transforms quantum state functions from inertial to certain noninertial reference frames is presented. This operator is applied to solve two well‐known problems: (1) the stationary state wave functions for a particle in a uniform gravitational field; (2) the motion and spreading of a Gaussian wave packet in a uniform gravitational field. The salient features of both analyses are discussed.

Particle spectrum
View Description Hide DescriptionData on elementary particle states are analyzed in a way that makes a number of regularities apparent. It is helpful to use a mass unit of approximately 1050 MeV, in terms of which the masses of a number of series of meson and baryon states can be represented approximately by M ^{2}=^{J}+const, where the constant is characteristic of a particular series. Individual series exhibit a remarkable regularity in the signs of space parity,Gparity,I spin, charge conjugationparity, and relative signs of resonant amplitudes.

Measurement of dielectric constants and capacitor dissipation using resonant circuits
View Description Hide DescriptionUsing basic theory of resonant R L C, equivalent capacitor circuits, and primarily uncalibrated, readily available apparatus, one can determine the dielectric constants of liquids and measure capacitor dissipation. The experiment described is suitable for both an intermediate level electricity and magnetism laboratory course and, with extensions, a more advanced course in dielectric theory.

Tumbling motion of free three‐dimensional wave packets
View Description Hide DescriptionA ’’moment of inertia’’ tensorI is defined for a quantum‐mechanical wave packet. The time evolution of I is investigated. It is shown that, for a free wave packet, the evolution of I is identical in form to that for a system of noninteracting classical particles. Several results involving the tumbling motion of the principal axis system of I are obtained.
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 Notes and Discussions


Comment on ’’Effect of the mass of the cord on the period of a simple pendulum’’
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The zilch cycle: An application of the first law of thermodynamics
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