摘要:

This paper shows that a conducting spiral behaves as a unipolar machine. As a first approximation, the current in the spiral can be viewed as a superposition of a system of circular currents, which provide a magnetic field perpendicular to the plane of the spiral, and a radial current on which the Ampere forces produce a self-torque. An essential feature of unipolar machines is stressed, i.e., the relevant electromagnetic interactions take place between perpendicular currents and not between parallel ones, as happens in the other machines. A simplified series unipolar machine for laboratory and classroom instruction has been built and is discussed.

ISSN:0002-9505    

DOI:10.1119/1.1976066

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

The form of the divergence operator in rectangular coordinates is derived by use of an infinitesimal spherical volume instead of the usual cubical one. The derivation shows clearly that the expression does not depend on the orientation of axes.

ISSN:0002-9505    

DOI:10.1119/1.1976068

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

In an earlier paper [Amer. J. Phys.36, 735 (1968)] of the same title one of us described a particularly simple method by which symmetry considerations can be applied to determine the possible forms of macroscopic laws. In this sequel we clarify the role of time-reversal symmetry, describe more fully the criteria for the occurrence of spontaneous electric and magnetic moments, discuss the application of the method to magnetically ordered systems, and correct a number of errors in the tables.

ISSN:0002-9505    

DOI:10.1119/1.1976070

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

The dependence of the high-energy large-angle scattering amplitude on the detailed shape of the partial wave distribution or impact parameter shape factor is considered. Transformations of the partial wave series and impact parameter representations are derived which make explicit the dependence on the “smoothness” of these shapes. The transformations are also used to construct examples of partial wave distributions and shape factors leading to analytic expressions for the scattering amplitude showing clearly the dependence on the “surface thickness” of the distributions.

ISSN:0002-9505    

DOI:10.1119/1.1976072

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

Propagation of a particular longitudinal disturbance on a semi-infinite one-dimensional lattice of identical mass particles coupled by identical massless ideal springs is studied. With all but one of the particles at rest and all the connecting springs at equilibrium length att = 0, the end particle is constrained to move with fixed longitudinal velocity for allt ≥ 0. Use is made of a method in which an infinite system of differential equations of motion is replaced by a single ordinary differential equation; the time-dependent Fourier coefficients of the equation's solution are the respective displacements from equilibrium of the individual lattice particles. These displacements and the corresponding velocities are expressed in terms of definite integrals. The results of velocity computations are presented along with asymptotic velocity distributions on the lattice and are discussed in relation to a simplified propagation description posited in a recent introductory textbook. The case of a semi-infinite elastic continuum subject to essentially the same initial and boundary conditions is worked out as a limit of the solution of the problem for the lattice.

ISSN:0002-9505    

DOI:10.1119/1.1976074

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

We give a diagrammatic representation of the diagonal form of the special Lorentz transformation. The null coordinatesx±ctare plotted along a single set of orthogonal axes. Special Lorentz transformations are then represented only by a change of scale along those orthogonal axes. This diagram, which we call a null coordinate diagram, and the Minkowski diagram are closely connected. To demonstrate the use of the null coordinate diagram, we apply it to the linear Doppler effect, time dilation, and Lorentz contraction.

ISSN:0002-9505    

DOI:10.1119/1.1976076

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

Using a method based only in group theory, and having in mind that many of today's experiments in EPR are done with paramagnetic crystals under external stress, we want to give those starting to work with this technique some idea how to write down a complete expression for the total interaction without assuming any model such as the spin Hamiltonian. This matrix interaction will have more parameters than the spin Hamiltonian, and we will decide the contribution of each one solely by experiment. We show the results of some experiments in transition and rare earth ions, and the equivalence between spin Hamiltonian parameters and the matrix interaction one.

ISSN:0002-9505    

DOI:10.1119/1.1976078

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

It is argued that the existence of the Pauli and Touschek transformations for the four-component neutrino field is a simple consequence of the fact that the basic wave function is a direct sum of two elementary spinors.

ISSN:0002-9505    

DOI:10.1119/1.1976080

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

Electromagnetic systems of finite mass(m > 0)and of zero mass(m = 0)are considered. For both cases the electromagnetic energy and momentum are computed and are shown to lead to essentially different formulas. An invariant expression for the electromagnetic mass inm > 0systems is derived. Allm > 0results are then specialized to the electrostatic case. Historical and present day confusion in the literature is discussed.

ISSN:0002-9505    

DOI:10.1119/1.1976082

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

A modification of the conventional driven vibrating string experiment is described which makes use of steel wires of various diameters and shows the effects of the stiffness of the wire on the tension required to make the wire resonate with the driving force.

ISSN:0002-9505    

DOI:10.1119/1.1976084

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP