ISSN:0002-9505    

DOI:10.1119/1.19054

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.19034

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.19022

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

We demonstrate a bandpass amplifier which can be constructed from common electronic components and has the surprising property that the group delay is negative in most spectral regions. A pulse propagating through a chain of such amplifiers is advanced by several milliseconds: the output waveformprecedesthe input waveform. Although striking, this behavior is not in conflict with causality, as demonstrated by experiments with pulses which start or end abruptly.

ISSN:0002-9505    

DOI:10.1119/1.18813

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

Student understanding and intuition for direct and reciprocal lattices can be enhanced using computer simulations of two-dimensional crystal structures and their diffraction patterns. Many important relationships can be presented very clearly in two dimensions, thus avoiding the added difficulty of visualizing structures in three dimensions. A number of examples are presented and the extension from two dimensions to three is discussed. The implementation of a program used for teaching is outlined.

ISSN:0002-9505    

DOI:10.1119/1.18816

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

A study of the gravitational interaction of a unit point mass moving external to(r>R)but under the influence of a fixed very thin ring of radiusRand mass ofM(M≫m)is presented. We consider the case when the motion of the point mass is restricted to the plane of the ring. With this restriction, it is possible to find trajectories for which the system has a positive total energy, and yet the point mass is bound to, and doomed to collide with, the ring. An example of a numerically iterated trajectory is included to support and illustrate this conclusion.

ISSN:0002-9505    

DOI:10.1119/1.18817

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

To resolve the challenges (paradoxes) attending the genesis of quantum theory, Niels Bohr in 1927 proposed a generalization of the conceptual framework of classical physics, termed complementarity, which posited pairs of classical concepts that could be manifested only in mutually exclusive experimental arrangements with both needed to embrace the full range of physical experience. In this context particle–wave complementarity has encountered two major obstacles; (1) No formulation of it has commanded a general consensus; and (2) empirical evidence abounds that contradicts the claim of mutual exclusivity of particle and wave properties of quantum objects in a single experiment. These problems are rooted in the unrestricted scope of this claim. It is shown that a restricted version of particle–wave complementarity, here called “which value–interference” complementarity, is consistent with observations, is naturally contained in the mathematical formalism of quantum theory and, in fact, holds in any representation of quantum theory defined by the eigenvectors of a complete set of commuting observables, such as the configuration space position (kinematic) variables or the complementary linear momentum (dynamic) variables. Thus, thewhich value–interferenceform of particle–wave complementarity exists within kinematic–dynamic complementarity, a “layered” complementarity, so to speak. It is hoped that a consistent and valid exposition of particle–wave complementarity will be helpful to those who find the framework of complementarity useful and appropriate for some purpose.

ISSN:0002-9505    

DOI:10.1119/1.18805

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

To remarkable accuracy and under a wide variety of conditions, the trajectories of projectiles under various laws of resistance may be approximated by cubic curves. This allows for the relatively simple calculation of many details of the flight.

ISSN:0002-9505    

DOI:10.1119/1.19023

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

We provide an elementary case study of field-induced quantum tunneling in a realistic three-dimensional environment which exhibits both tunneling and classically allowed motion. An analytic description is presented for ballistic motion in a uniform electric field. From there we derive simple expressions concerning the wave function for field emission from an ultrathin quantum well in the tunneling limit. At the same time a wave-packet description of the tunneling process is obtained. The tunneling time can be read off from the lateral spread of the tunneling current distribution.

ISSN:0002-9505    

DOI:10.1119/1.18806

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP

摘要:

The Fréedericksz transition is a magnetically induced reorientation of the molecules of a liquid crystal. We describe here an experimental investigation of the Fréedericksz effect in liquid crystals for the advanced undergraduate laboratory. Besides introducing students to the novel and fascinating liquid-crystalline state of matter, the experiment serves as a valuable introduction to light propagation in an optically anisotropic medium and to the use of the calculus of variations in a somewhat unusual context. All components for the experiments are readily available and inexpensive.

ISSN:0002-9505    

DOI:10.1119/1.18807

出版商:American Association of Physics Teachers    

年代:1998

数据来源: AIP