摘要:

Dr. Immanuel Estermann was engaged in writing a book on the History of the Molecular Beam Method when he died in Haifa, Israel on 31 March 1973. The original plan of the manuscript was to cover three distinct historical periods: the first, the years 1911–1933, when the center of research in molecular beams was at the University of Hamburg; the second, from 1933 to the outbreak of World War II, when the most active laboratory working in the field was at Columbia University; and the postwar period, when many laboratories on both sides of the Atlantic became actively engaged in this field. The material in this paper deals primarily with the early historical period and would have formed the essence of the first two chapters of the book. In addition to presenting interesting historical facts on a crucial period in the development of quantum physics, it contains some amusing historical sidelights on the research personalities that dominated that period.

ISSN:0002-9505    

DOI:10.1119/1.9747

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

Two complementary, thin screens treated in the Babinet principle have one thing in common, the line of their edges. Employing the assumption that scattering of electromagnetic waves from a thin, conducting screen is solely from the elements of the edges, we have made a simple derivation of the Babinet principle in electromagnetic form. We needed to treat but one element of edge with the aperture and conductor interchanged. The factors which affect the amplitudes and phases of the electric and magnetic scattered wavelets reaching any point of observation from the common element of edge of the complementary screens are identical except for phase factors of 0° or 180° caused by polarization effects at the conducting edge. Symmetry conditions from electromagnetic theory yield those factors. We have illustrated the Babinet principle in electromagnetic form by tabularly expressing the scattered waves from two complementary half‐planes. These results also were based on the assumption that scattering by a thin screen is solely from the edges.

ISSN:0002-9505    

DOI:10.1119/1.9748

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

Non‐Hermitian Hamiltonians are used in many research areas as approximate models of physical systems, for example, the optical‐model potential in nuclear physics. Such Hamiltonians are rarely treated in introductory quantum mechanics. Here the quantum scattering problem of a two‐state system is treated exactly for the case of one‐dimensional square‐well potentials. By introducing an appropriate optical‐model potential, an approximate solution for one of the two states is obtained. The exact and approximate solutions are compared for a realistic example.

ISSN:0002-9505    

DOI:10.1119/1.9749

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

The filamentary current loop of magnetostatics is naturally associated with toroidal topology rather than the usual cylindrical or spherical topology. The field near the wire is best explored in toroidal coordinates, but even the far magnetic dipole field may be found this way. The loop field becomes infinite near the wire just as does the endless straight wire field, but another, not well‐known logarithmic infinity occurs that is proportional to the curvature. We demonstrate these facts and, in addition, mention a certain duality with the electric field of a ring of charge.

ISSN:0002-9505    

DOI:10.1119/1.9750

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

If the Hamiltonian for the motion of a charged particle in a magnetic field has one or more cyclic coordinates, it may often be viewed as representing the motion of a particle subject to a potential V. The use of V provides qualitative insight about the motion even in some cases where a solution of the motion cannot be obtained. Several examples using this concept are reviewed and discussed.

ISSN:0002-9505    

DOI:10.1119/1.9714

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

A one‐semester course in introductory stellar astrophysics at the advanced undergraduate level is described. The course aims to integrate all previously learned physics by applying it to the study of stars. After a brief introductory section on basic astronomical measurements, the main topics covered are stellar atmospheres, stellar structure, and stellar evolution. Problem assignments are designed to encourage the use of the computer and of current astronomical literature.

ISSN:0002-9505    

DOI:10.1119/1.9715

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

The reciprocal lattice is frequently generated as a by‐product of the direct lattice or as a convenient abstraction which satisfies the Laue equations. The dualistic point of view from projective geometry is invoked to characterize the information contained in the reciprocal lattice more precisely. From this point of view the reciprocal lattice is seen as an alternate and equally complete representation of the geometric structure of crystal systems. The Ewald and Bragg constructions are displayed as symmetric constructions in their respective lattices.

ISSN:0002-9505    

DOI:10.1119/1.9716

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

Niels Bohr has often pointed out that already the simplest quantum rule, ΔE = hν, is irrational insofar as ΔE stands for a timeless energy jump, whereas a frequency ν is defined only over a long time span. However, when this irrational relation is accepted as a mainstay of the quantum theory, one cannot reject a corresponding irrationality for momentum jumps Δp connected with periodicities in space, the less so as it yields a unitary mechanical explanation of all wavelike‐looking phenomena of matter, in particular those of the diffraction of electrons, without resorting to any wave interference in space. (This has nothing to do with the complex–imaginary wave function ψ, which has a purely statistical significance.) We therefore propose to regard matter particles as real physical entities as always, in contrast to the matter waves with λ = h/p as a suggestive yet expendable fiction, permitting a return from dualism to unity, a simplification of the customary interpretation of standard quantum effects, also suggesting a long overdue reform in the teaching of the elements of quantum mechanics.Editor’s note: This is the fourth and last in a series of articles begun ten years ago in this Journal. Earlier parts in the series may be found in American Journal of Physics 33, 123 (1965); 34, 1160 (1966); and 37, 541 (1969).

ISSN:0002-9505    

DOI:10.1119/1.9717

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

A simple macroscopic theory of elastic rods is presented in which all assumptions but one are consistent with both Newtonian mechanics and special relativity. The one distinguishing assumption is the inertial equivalence of energy. While invariance of the theory under Lorentz transformations is proved, all physical consequences—including the stress and velocity dependence of the length and inertial mass of a rod as well as the velocities of sound through it—are derived and can be tested in any one inertial frame. Exact wave solutions of the basic equations are obtained for an idealized elastic material in which the velocity of sound is independent of amplitude. These solutions are used to account for the kinematics and dynamics of accelerated rods, including the time‐dependent processes which result in their overall Lorentz contraction.

ISSN:0002-9505    

DOI:10.1119/1.9718

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP

摘要:

A geometric model is developed to interpret the physical meaning of various major characteristics of ’’real’’ holograms. Without invoking highly mathematical principles, but, at the same time, without sacrificing basic physics, the model allows the development of an intuitive understanding of the following characteristics: the virtual image, the real image, redundancy, multiple scenes, white light or Lippmann–Bragg reflection holograms; and then leads into the explanation of the hypothetical ’’thin’’ hologram.

ISSN:0002-9505    

DOI:10.1119/1.9719

出版商:American Association of Physics Teachers    

年代:1975

数据来源: AIP