摘要:

Using thermodynamics as an analogy, an ‘‘electricity machine’’ is constructed and analyzed. This machine runs through a ‘‘Carnot’’ cycle. The analysis leads to the construction of a ‘‘new’’ quantity called ‘‘reduced electricity’’ (charge). The example shows what life in electrodynamics would be without the substancelike quantity which we call electrical charge. (This state of affairs is accepted in thermodynamics.) Imagine the development of the theory of electricity had fallen into the hands of the thermodynamicists. As fairy and other tales go, they have an air of surrealism surrounding them.

ISSN:0002-9505    

DOI:10.1119/1.14787

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

The formal theory of multiple scattering in quantum mechanics is adapted to one dimension and applied to the basic problem of scattering by a double delta‐function potential. The multiple scattering method is shown to provide a much more powerful analysis than is obtained by either the one‐dimensional partial wave approach or by the standard differential solution to the Schrödinger equation.

ISSN:0002-9505    

DOI:10.1119/1.14788

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

In elementary texts, derivations of the equationI=I0[exp(qV/kT)−1] (the ‘‘simple diode’’ equation) all depend on conditions valid when no current flows, an apparently contradictory situation. Because introductory texts justify this only qualitatively, it is desirable to do an explicit calculation which explores the limits of the equation when current actually does flow—a procedure carried out in this paper by manipulating the current density equations and integrating them across the space‐charge layer (SCL). The calculation shows the ‘‘simple diode equation’’ to be valid if the width of the SCL is small compared to the diffusion length of either an elecron or a hole. This implies relatively few collisions in the SCL and thus clarifies why SCL recombination may also be neglected in the ‘‘simple diode’’ regime.

ISSN:0002-9505    

DOI:10.1119/1.14790

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

The field intensity behind a moving (nonrelativistic) occulting object has a rather counterintuitive behavior at sufficiently large distance: finite transit time effects yield two simultaneous shadow paths on a plane, which separate from each other with superluminal velocity.

ISSN:0002-9505    

DOI:10.1119/1.14868

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

A method for determining the band gap in germanium and silicon at 0 K based upon the temperature dependence of the electrical conductivity of ap‐njunction is described. Results are given for the band gaps that are in good agreement with the accepted values.

ISSN:0002-9505    

DOI:10.1119/1.14791

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

The Feynman–Hellmann theorem is employed to derive simple expressions for the expectation values of particular powers of the radial coordinate for a class of central or hypercentral force problems. The results are applied to the Kratzer, the modified oscillator, and the hyperspherical oscillator potentials.

ISSN:0002-9505    

DOI:10.1119/1.14792

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

Through a series of short steps we try to make clear why the classical–quantal dualism is still indispensable, despite the advances in our understanding of quantum physics.

ISSN:0002-9505    

DOI:10.1119/1.14793

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

We give some illustrations and interpretations of supersymmetry in quantum mechanics in simple models. We show that the value of 2 for thegfactor of the electron expresses the presence of supersymmetry in the Hamiltonian for an electron in a uniform magnetic field. The problem is considered both in the Schrödinger and Dirac formulations. We also show that the radial Coulomb problem with orbital angular momentuml, nuclear chargeZ, and principal quantum numbern, is supersymmetrically linked to the similar problem with chargeZ(1−1/n) and quantum numbern−1. Thereby the dependence of Coulomb energies only on the combinationZ/nis seen as a manifestation of the supersymmetry in the radial Coulomb problem. Other examples of supersymmetry we consider are the Morse potential, the three‐dimensional isotropic oscillator, the states of the helium atom and those of the hydrogen atom in an extremely strong magnetic field.

ISSN:0002-9505    

DOI:10.1119/1.14794

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

We discuss an elementary example of how, in a strong gravitational field, the basic kinematical concepts of acceleration and circular motion seem to have paradoxical properties. This allows an insight into the physical significance of space‐time curvature without the use of difficult mathematical formalism.

ISSN:0002-9505    

DOI:10.1119/1.14795

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP

摘要:

An undergraduate experiment is described that illustrates the period doubling route to chaos in a simple dissipative mechanical system, a bouncing ball subject to repeated impacts with a vibrating table.

ISSN:0002-9505    

DOI:10.1119/1.14796

出版商:American Association of Physics Teachers    

年代:1986

数据来源: AIP