ISSN:0002-9505    

DOI:10.1119/1.17352

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

This is the edited text of the Klopsteg Lecture delivered to the Summer Meeting of the AAPT on August 13, 1992. It sketches the current state of knowledge about the violin—at least as seen by the author—in two parts,PhysicsoftheBowedStringandTheViolinasaRadiatorofSound, punctuated by a number of ‘‘meditations’’ about the nature of scientific knowledge.  

ISSN:0002-9505    

DOI:10.1119/1.17353

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

An analysis of Brownian motion based upon a ‘‘Langevin equation’’ form of Newton’s second law provides a physically motivated introduction to the theory of continuous Markov processes, which in turn illuminates the subtle mathematical underpinnings of the Langevin equation. But the Langevin approach to Brownian motion requires one toassumethat the collisional forces of the bath molecules on the Brownian particle artfully resolve themselves into a ‘‘dissipative drag’’ component and a ‘‘zero‐mean fluctuating’’ component. A physically more plausible approach is provided by a simple discrete‐state jump Markov process that models in a highly idealized way the immediate effects of individual molecular collisions on the velocity of the Brownian particle. The predictions of this jump Markov process model in the continuum limit are found to precisely duplicate the predictions of the Langevin equation, thereby validating the critical two‐force assumption of the Langevin approach.

ISSN:0002-9505    

DOI:10.1119/1.17354

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

A method due to Copson for treating the electrostatics of a disk is modified so that each step can be understood physically. Using this method we easily find the capacitance 2a/π and the electric polarizability 4a3/3π of a conducting disk. We also find in closed form the Green’s function along the axis and the self‐force (the force due to induced charges) on a point charge on the axis. We similarly treat magnetic problems, finding the normal polarizability of a superconducting disk and the ‘‘levitating’’ force on a point monopole or vertical point dipole on the axis. All results are in closed form.

ISSN:0002-9505    

DOI:10.1119/1.17355

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

A popular demonstration which often accompanies the introduction of magnetic induction is that in which a strong button‐shaped magnet is dropped through a long copper or aluminum tube. The induced currents cause a retarding force which dramatically slows the descent of the falling magnet. Here, we describe methods of calculating and measuring the terminal velocity and magnetic forces in the magnetic braking experiment. The techniques are quite accurate, inexpensive to perform, and are suitable for introductory courses in electricity and magnetism.

ISSN:0002-9505    

DOI:10.1119/1.17356

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

After a short introduction to response functions, the force‐acceleration response function is calculated for a forced classical semi‐infinite linear chain. This response function, which can be called a frequency‐dependent inverse effective mass, allows a thorough and graphical discussion of motions and energy transport in the chain. The nature of extended motions for forcing frequencies within the band and of localized surface modes for high frequencies is clearly shown by this treatment.

ISSN:0002-9505    

DOI:10.1119/1.17357

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

The random walk in one dimension can be effectively used to introduce or reinforce a number of advanced mathematical and physical concepts. Here the behavior of an ensemble of particles executing random walks is discussed as an eigenvalue problem, and as a system for which entropy can be calculated in a nonequilibrium state.

ISSN:0002-9505    

DOI:10.1119/1.17443

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

Measurement of energy distribution curves (EDCs) is one of the more powerful techniques for investigating the electronic band structure of solids. It would be profitable for undergraduate students to perform an experiment introducing them to this aspect of modern spectroscopy. In this paper we describe an arrangement we use in our course of modern physics for engineering students utilizing a commercial photocell. After a theoretical background on the photoemission process in metal, we present measurements on the EDCs obtained by graphical differentiation of theI–Vcharacteristics of the photocell and by using an ac method where the differentiation is performed electronically.

ISSN:0002-9505    

DOI:10.1119/1.17358

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

The problem of scattering in one dimension by a potential which consists ofNidentical cells is solved in a transparent manner. TheN‐cell transmission and reflection amplitudes are expressed in terms of the single‐cell amplitudes and the Bloch phase. As examples the results are applied to a row of delta‐function potentials, and to a row of square wells, and it is shown that these expressions provide an immediate understanding of the results of detailed calculations.

ISSN:0002-9505    

DOI:10.1119/1.17306

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

A new integrated computer‐assisted personalized assignment (CAPA) system that creates individual assignments for each student has been developed and found to be a powerful motivator. The CAPA system allows students to enter their answers to personalized assignments directly via networked terminals, gives immediate feedback and hints (allowing challenging questions), while providing the instructor with on‐line performance information. The students are encouraged to study together which is known to be an effective learning strategy, but each must still obtain his/her own correct answers. Students are allowed to re‐enter solutions to the problems before the due date without penalty, thus providing students with different skills levels the opportunity and incentive to understand the material without being judged during the learning process. The features and operation of the system are described, observations on its use in an introductory general physics class are reported, and some of the highly favorable student reactions are included.

ISSN:0002-9505    

DOI:10.1119/1.17307

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP