Showing papers in "American Journal of Physics in 1951"
1,137 citations
1,082 citations
TL;DR: In this article, the forces acting on an arbitrary portion of an electrically or magnetically polarized body are calculated without introduction of energy arguments, of an atomic model of the polarization, or of assumptions in regard to the physical significance of the macroscopic field vectors within polarized matter.
Abstract: In I, the forces acting on an arbitrary portion of an electrically or magnetically polarized body are calculated without introduction of energy arguments, of an atomic model of the polarization, or of assumptions in regard to the physical significance of the macroscopic field vectors within polarized matter. It is pointed out that a magneto-mechanical formula derived by use of amperian currents and one derived by use of magnetic poles will, in general, require different “stress” systems in a given physical situation, because a part of the force that is included in the long-range force in one calculation is attributed to stresses in the other. In the present treatment, dipole-dipole interactions are taken as fundamental; poles and amperian currents are regarded as purely formal devices; and the two are treated on an equal footing, so that two equivalent sets of formulas are obtained. In II, the general formulas of I are specialized to the case of a fluid. Formulas relating to electrostriction and to the effect of immersing a body in a fluid are derived; their relation to the traditional formulas (based on energy arguments) is discussed.
89 citations
TL;DR: In this paper, the use of the zone plate for focusing transmitted wavelengths ranging from the infrared to the very soft x-ray region is discussed, and an investigation is made of the focal and chromatic properties of a zone plate to be used for visible and near ultraviolet light.
Abstract: Methods of construction of transmission zone plates are considered. The use of the zone plate for focusing transmitted wavelengths ranging from the infrared to the very soft x-ray region is discussed. An investigation is made of the focal and chromatic properties of a zone plate to be used for visible and near ultraviolet light. Photographs of several lines of the mercury spectrum made by using a zone plate as the focusing “lens” are exhibited. The similarity between the optical properties of a transmission zone plate and a converging lens are shown by both theoretical considerations and experiment.
81 citations
TL;DR: In this article, it was shown that the law of sines was experimentally discovered independently in England by Thomas Hariot and his friends, and was used by them several years before 1621.
Abstract: The law of refraction known by the name of Snell's law was circulated in manuscript by him as early as 1621. This paper shows that the law of sines was experimentally discovered independently in England by Thomas Hariot and his friends, and was used by them several years before 1621.
57 citations
39 citations
TL;DR: In this paper, the authors introduce the concept of basic concepts of nuclear physics, including the force between nucleons, nuclear models, and radioactive decay, and apply them to a wide range of applications.
Abstract: BASIC NUCLEAR STRUCTURE. Basic Concepts. Elements of Quantum Mechanics. Nuclear Properties. The Force Between Nucleons. Nuclear Models. NUCLEAR DECAY AND RADIOACTIVITY. Radioactive Decay. Detecting Nuclear Radiations. Alpha Decay. Beta Decay. Gamma Decay. NUCLEAR REACTIONS. Nuclear Reactions. Neutron Physics. Nuclear Fission. Nuclear Fusion. Accelerators. EXTENSION AND APPLICATIONS. Nuclear Spins and Moments. Meson Physics. Particle Physics. Nuclear Astrophysics. Applications of Nuclear Physics.
35 citations
22 citations
TL;DR: In this article, a descriptive and explanatory account of the facts and methods of artificial radioactivity and transmutation, including properties of nuclear radiations, means of detection of nuclear particles, technique of artificial acceleration, energy relationships in reactions, the manufacture and counting of radioactive elements, isotopes, nuclear fission, and kindred subjects.
Abstract: This book offers a descriptive and explanatory account, for class use, of the facts and methods of artificial radioactivity and transmutation, including properties of nuclear radiations, means of detection of nuclear particles, technique of artificial acceleration, energy relationships in reactions, the manufacture and counting of radioactive elements, isotopes, nuclear fission, and kindred subjects.
22 citations
TL;DR: In this article, it is shown that it is not possible to represent the magnetic field of a linear circuit carrying a steady current by such an assemblage of lines of force which are everywhere continuous.
Abstract: Assemblages of lines of force are widely used to represent electric and magnetic fields, the density of lines in the neighborhood of a point being proportional to the intensity of the vector at that point. It is not generally recognized, however, that the properties of continuity and individuality of such lines are irrelevant so far as observable electromagnetic phenomenon are concerned.Contrary to widely held views, it is not possible generally to represent the magnetic field of a linear circuit carrying a steady current by such an assemblage of lines of force which are everywhere continuous. This is because the continuous magnetic lines of force do not generally form simple closed curves, which each link the circuit just once. The interlinkage which is significant is that between the circuit and arbitrarily chosen closed paths of integration of the magnetic vector.
TL;DR: The importance of emphasis on ideas rather than facts in physics courses has been emphasized in this paper, except insofar as they are necessary to illustrate the ideas, which is not always the case.
Abstract: Observations upon the teaching of physics, with special reference, in the case of courses intended for cultural purposes, to the importance of emphasis on ideas rather than facts, except insofar as they are necessary to illustrate the ideas.
TL;DR: The mathematical papers of Thomas Hariot (1560-1621) show clearly that Hariot not only experimented with number systems, but also understood clearly the theory and practice of binary numeration nearly a century before Leibniz's time.
Abstract: Though it is frequently stated that binary numeration was first formally proposed by Leibniz as an illustration of his dualistic philosophy, the mathematical papers of Thomas Hariot (1560–1621) show clearly that Hariot not only experimented with number systems, but also understood clearly the theory and practice of binary numeration nearly a century before Leibniz's time.
TL;DR: By introducing the concept of a "dimension space" whose coordinates are the exponents of the basic dimensions of physical quantities, the proof of Buckingham π-theorem is transformed into a simple geometrical problem as discussed by the authors.
Abstract: By introduction of the concept of a “dimension space,” whose coordinates are the exponents of the basic dimensions of physical quantities, the proof of Buckingham π-theorem is transformed into a simple geometrical problem.
TL;DR: In this article, it was shown that unless the body is spherical, the angular momentum vector also nutates in the course of the precession, a phenomenon caused by the deviation of the torque on the body from the customary, but here incorrect, expression M×B.
Abstract: A frequently used classical analog to the quantum precession of a magnetic moment in a magnetic field is the motion in a uniform static magnetic field of a symmetrical rigid body charged so that the ratio of charge to mass density is uniform. In general, the figure axis of such a magnetic top both precesses and nutates, and the mechanism producing the nutation is qualitatively different from that responsible for the nutation of the familiar gravitational top. Unless the body is spherical the angular momentum vector also nutates in the course of the precession, a phenomenon caused by the deviation of the torque on the body from the customary, but here incorrect, expression M×B. The uniform precession frequency of the magnetic top is not the Larmor frequency but involves in addition terms depending on higher powers of the magnetic field, a correction which corresponds to the quadratic Zeeman effect.
TL;DR: In this paper, an iron bob swinging as a pendulum along the axis of a coil toward and away from its center is maintained in motion by feeding alternating current from a low resistance source into the coil which forms part of a suitably tuned circuit.
Abstract: An iron bob swinging as a pendulum along the axis of a coil toward and away from its center is maintained in motion by feeding alternating current from a low resistance source into the coil which forms part of a suitably tuned circuit. The iron bob may be replaced by a second coil connected in series. The transfer of energy to the pendulum is shown to be due to the phase difference between the variation in the inductance of the circuit and the corresponding variation in the amplitude of the current with the oscillation of the pendulum: if the variation in the current amplitude lags behind the variation in inductance, the pendulum is driven, otherwise it is damped. In the limit of small amplitude of oscillation the condition for maintenance is that the circuit have predominantly inductive reactance and sufficiently high Q.
TL;DR: Several new popular science magazines, such as Omni z and Science 80, have been established to serve the public's interest in science and have been shown or repeated at different times in different areas of the country as discussed by the authors.
Abstract: Issues and events such as Three Mile Island, I the synthetic fuels controversy, toxic chemical wastes, “test-tube babies, ” artificial insemination projects, the safety of the DC-10, and the crash of Skylab are obviously increasing the public’s interest in science. Recently several new popular science magazines, such as Omni z and Science 80, have been established to serve thk interest. TMs upsurge in printed science journalism is being paralleled by the growth of science programs on television. In this essay, I will briefly describe the new science TV shows. Figure 1 lists the networks’ addresses, since many of the programs can be rented or bought for classroom use. The programs are shown or repeated at different times in different areas of the country. Current
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TL;DR: In this article, the problem of describing the state of order in a binary alloy is considered and a set of order parameters is defined in the following way: pi is the probability that if a given site is occupied by a B atom, then a site which is its ith neighbor is not occupied by an A atom.
Abstract: The problem of describing the state of order in a binary alloy is considered. A set of order parameters is defined in the following way: pi is the probability that if a given site is occupied by a B atom then a site which is its ith neighbor is occupied by an A atom. The relationships of this set to the parameters used by other authors are discussed.
TL;DR: In this paper, it is shown that a heat engine can be made to convert heat to work without other changes in its immediate system, provided that an outside observer creates in the system a negative information entropy equal to the negative entropy change involved in the operation of the engine.
Abstract: The failure of a heat engine to defeat the second law of thermodynamics by using density fluctuations to convert heat to work without leaving other changes in the universe is usually explained by saying that the fluctuations of the engine itself would defeat such an operation or that the microscopic nature of the fluctuations prevents their being put to a macroscopic use. It is shown here that with a proper definition of stored information, a heat engine can be made to convert heat to work without other changes in its immediate system, provided that an outside observer creates in the system a negative information entropy equal to the negative entropy change involved in the operation of the engine. This equivalence of a communication entropy change to a thermodynamic entropy change leads to the definition of the entropy of a nonequilibrium system as the algebraic sum of the thermodynamic entropy which the system would have at equilibrium and the information entropy necessary to construct the specified stat...
TL;DR: In this paper, the authors describe the construction and scale of the standard, the use of Hooke's scale in meteorological diaries of the period 1669 to 1709, and its modification by Francis Hauksbee, the Younger, in the early eighteenth century.
Abstract: Between 1663 and 1665, Robert Hooke designed a thermometer for the Royal Society which served as a standard for the graduation of other seventeenth-century instruments. This paper describes the construction and scale of the standard, the use of Hooke's scale in meteorological diaries of the period 1669 to 1709, and its modification by Francis Hauksbee, the Younger, in the early eighteenth century. It includes a suggestion for interpretation of the barometric observations in Hooke's Guildhall diary. It points out the influence of the Royal Society's meteorological observations in the age of Fahrenheit, Reaumur, and Celsius.
TL;DR: The use of Atwood's machine in illustrating the principles of the application of Newton's second law to a simple physical system, whose connected parts have both rotational and translational motion, is shown in this paper.
Abstract: The use of Atwood's machine in illustrating the principles of the application of Newton's second law to a simple physical system, whose connected parts have both rotational and translational motion, is shown. A diagram which shows the forces acting on all the component masses is drawn, and this picture facilitates the setting-up of the appropriate F = ma and τ = Iα equations. The moment of inertia of the pulley, the friction in its bearings, and the mass of the string are included in the accelerating system in a natural way. The observed acceleration of the hanging masses can be compared with that computed by this method.
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TL;DR: The discovery of neutrons produced by the cosmic radiation is reviewed, and the evidence today available is summarized in this article, where the life history of a neutron in the atmosphere is discussed, as is its eventual capture to form radiocarbon.
Abstract: The discovery of neutrons produced by the cosmic radiation is reviewed, and the evidence today available is summarized. The life history of a neutron in the atmosphere is discussed, as is its eventual capture to form radiocarbon. The latitude effect and altitude dependence are presented. Some of the possible production-processes are discussed.
TL;DR: In this paper, the authors make a complete break with the past and explain the diffraction pattern on the basis of Thomas Young's theory, which is an interference pattern between the incident wave and secondary waves from the edge of the aperture.
Abstract: Measurements of the diffraction pattern of microwaves near circular apertures reveal the quantitative correctness of Kirchhoff's obliquity factor. It has been customary in textbooks of physical optics to assume with Fresnel that the amplitude from zones an infinite distance from the center of the aperture is zero. However, according to Kirchhoff's equation, the amplitude from a zone as the zone number increases without bound is not zero but half the amplitude from the central zone. It is noted that a marginal correction in the textbooks will give results that agree not only with the observed behavior of light, but of microwave diffraction as well, up to the plane of the aperture. The more daring instructor may wish to make a more complete break with the past and explain the diffraction pattern on the basis of Thomas Young's theory. By Young's simple theory that the diffraction pattern of the aperture is an interference pattern between the incident wave and secondary waves from the edge of the aperture, th...