摘要:

Null‐length springs, in spite of being apparently simple, reveal several unexpected properties. All of these stem from the fact that these springs, lacking a characteristic length, show no differences between longitudinal and transverse vibrations. Some of these qualities are demonstrated in an elementary way so as to show the underlying physics. The properties proved are used to obtain certain well‐known results of introductory physics. Finally, an experimental setup is described briefly to simulate null‐length springs.

ISSN:0002-9505    

DOI:10.1119/1.16523

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

The threshold amplitude for Compton scattering is known to be proportional to the square of the total charge of the target. A naive application of the impulse approximation would give a result that would depend upon the sum of squares of the charges of the individual particles comprising the target. Resolution of these incompatible results depends upon careful treatment of the center‐of‐mass coordinate of the target. This treatment is presented in the context of nonrelativistic perturbation theory.

ISSN:0002-9505    

DOI:10.1119/1.16524

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

Elementary numerical methods are used to evaluate solutions to Schrödinger’s equation for a variety of one‐dimensional potential barriers and to determine the transmission coefficients of free particles. These techniques are used to study the oscillatory variations in transmission coefficients for both continuous and discontinuous potentials. The amplitude of the variations is found to be strongly increased by discontinuities in the potential function but small variations exist even for a smooth, continuous potential function. The techniques described are suitable for intermediate‐level undergraduate physics students.

ISSN:0002-9505    

DOI:10.1119/1.16525

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

An experiment is described in which the speed of light is measured by time of flight. The equipment in this experiment includes a laser and an acousto–optic modulator. A laser beam was rapidly switched on and off by an acousto–optic modulator and the time that was taken for a light pulse to go a known distance was measured. The group velocity of light was found to an accuracy of about 1.5% using a calibrated oscilloscope as the time reference. Further, by making a least‐squares fit to a set of measurements for different travel times, an uncertainty of 0.5% was obtained. This experiment illustrates acousto–optic modulators, optics, time‐of‐flight instrumentation, and data analysis.

ISSN:0002-9505    

DOI:10.1119/1.16526

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

A widely recognized problem that physics teachers encounter is the difficulty that most students have when solving problems related to magnetic field line distributions in the presence of hard‐ and softmagnetic materials. Two causes of these difficulties are identified: (1) The fact that the hysteresis is introduced as the typical behavior of ferromagnetic materials; (2) the fact that the magnetic field strengthHis almost absent in the electromagnetism course. Proposals to remedy the student’s problems are (a) to introduce four idealized magnetic materials, i.e., unmagnetic, hardmagnetic, softmagnetic, and superconducting materials; and (b) to use the magnetic field strengthH, and not the magnetic inductionB, when discussing problems of magnetostatics.

ISSN:0002-9505    

DOI:10.1119/1.16831

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

The internal energy and chemical potential of a noninteracting Fermi gas has been evaluated in three ways: numerically (applicable to arbitrary temperatures), through an asymptotic power series expansion (suitable for low temperatures), and by means of standard Padé approximants (appropriate for low and moderate temperatures). The main conclusion of this work is that the Padé approximant, which is constructed from the asymptotic series employing only minimal labor, is far superior to the truncated series expansion.

ISSN:0002-9505    

DOI:10.1119/1.16827

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

Using the particle–mesh (PM) method, a one‐dimensional simulation of the well‐known Langmuir–Child’s law is performed on an INTEL 80386‐based personal computer system. The program is coded inturbo basic(trademark of Borland International, Inc.). The numerical results obtained were in excellent agreement with theoretical predictions and the computational time required is quite modest. This simulation exercise demonstrates that some simple computer simulation using particles may be implemented successfully on PC’s that are available today, and hopefully this will provide the necessary incentives for newcomers to the field who wish to acquire a flavor of the elementary aspects of the practice.

ISSN:0002-9505    

DOI:10.1119/1.16527

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

Qualitatively the same experiment can reveal either the particle behavior, or the wave behavior, or even intermediate behaviors, if the experiment is performed in each case with adequate parameters. A simple parametrized double‐slit apparatus can be built for this purpose. This helps to make more explicit the idea of particle–wave duality. An ‘‘interpretation function’’ is also defined to estimate the possibilities of interpretation.

ISSN:0002-9505    

DOI:10.1119/1.16528

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

摘要:

A spreadsheet is used to calculate numerical values for the eddy current/induced electric field distribution produced by a time‐varying magnetic field in a saline solution. The value of each cell corresponds to the current density of a loop in the object. It is related to the current densities in its neighboring cells and the resistivities of their borders. The resulting set of equations is solved by iteration. Comparisons of the two components of the induced field are made with analytical solutions and with experimental values measured by a dual dipole antenna system. Such analyses can be used to provide students with a better understanding of the induced field distribution in irregularly shaped objects.

ISSN:0002-9505    

DOI:10.1119/1.16529

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16530

出版商:American Association of Physics Teachers    

年代:1991

数据来源: AIP