摘要:

This paper narrates learning as it evolved through experimental work and interpretation in two distinct investigations: the explorations of permanent magnets and needles conducted by a student, Joann, as I interactively interviewed her, and Faraday’s initial experimenting with diamagnetism, as documented in hisDiary. Both investigators puzzled over details, revisited their confusions resiliently, and invented analogies as ways of extending their questioning; “misconceptions” and conflict were not explicit to their process. Additionally, Faraday formed interpretations—and doubts critiquing them—that drew upon his extensive experience with magnetism’s spatial behaviors. These two cases suggest that physics instruction could include opportunities for students’ development of their own investigatory learning.

ISSN:0002-9505    

DOI:10.1119/1.18675

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

A prescription for computing the symmetric energy–momentum tensor from the field equations is presented. The method is then used to obtain the total energy and momentum for the electromagnetic field described by Maxwell electrodynamics, Born–Infeld nonlinear electrodynamics, and Podolsky generalized electrodynamics, respectively.

ISSN:0002-9505    

DOI:10.1119/1.18676

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

A simple potential model is used to study the contribution of negative energy states to the static electric polarizability of a relativistic particle which is bound by a one-dimensional delta potential. The potential includes both Lorentz scalar and vector components. Contrary to the result based on nonrelativistic physics, we find it possible that the electric polarizability can have a negative sign.

ISSN:0002-9505    

DOI:10.1119/1.18677

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

We consider the statics and dynamics ofNidentical magnetic dipoles, with inertia, pinned at the corners of a regular polygon withNsides. We show that at equilibrium all dipoles are aligned tangent to the circumscribed circle. We find the normal modes and frequencies for oscillations about equilibrium, and discuss the dispersion relation. In the highest frequency normal mode the dipoles oscillate in phase with equal amplitudes, so no magnetic dipole radiation is emitted. In the limitN→∞,the equilibrium energy and the frequency of the symmetric mode are both related to ζ(3), where ζ is the Riemann zeta function.

ISSN:0002-9505    

DOI:10.1119/1.18678

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

An intuitive, straightforward way of finding the metric of a rotating black hole is presented, based on the algebra of differential forms. The representation obtained for the metric displays a simplicity which is not obvious in the usual Boyer–Lindquist coordinates.

ISSN:0002-9505    

DOI:10.1119/1.18679

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

We propose some simple experiments to measure moments of inertia of certain physical pendula having high and low symmetry. Periods of oscillation, mass, and distance of the pivot from the center of mass are used to measureICMfor: (a) the “floating eagle,” an intriguing toy, and (b) a rectangular plate. Values ofICMobtained from measurements about different parallel axes may be checked for consistency.

ISSN:0002-9505    

DOI:10.1119/1.18680

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

A simultaneous mean-field treatment, of both phenomena, ferro- and antiferromagnetism, in the framework of the Bragg–Williams theory, shows the importance of the interplay between the two corresponding order parameters in determining the features of the phase diagram. The problems of phase separation and order–disorder transition in binary alloys are also included in the solution. The different projections of the phase diagram are discussed.

ISSN:0002-9505    

DOI:10.1119/1.18681

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

The magnetostatic field of an infinite rectilinear current placed in the stationary gravitational field of a rotating cosmic string is found. An interesting aspect of this problem is that although the metric is mathematically very simple, its physical meaning is not trivial. It depends only on topological parameters. So, the cosmic string vacuum space–time is locally equivalent to the Minkowski space–time, but not globally. The calculations are so simple that they can easily be shown in the classroom.

ISSN:0002-9505    

DOI:10.1119/1.18682

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

Two experiments are presented to introduce undergraduate students in electrical engineering or physics to modern optical signal processing. Both experiments use an acousto-optic (AO) Bragg cell together with additional electronics to modify the intensity of a laser beam. Specifically, we show how an AO feedback system operating in the Bragg regime can be configured to produce amplitude modulated (AM) and pulse-width modulated optical signals. The basic components of the AO feedback system include a laser, an AO Bragg cell, an electronic AM modulator, a photodetector, an amplifier, and an electronic adder. Except for the laser, the AM modulator, and the Bragg cell, each of these components can be constructed with low cost electronics. A tutorial outlining the principles of acousto-optics is included to provide sufficient understanding of the Bragg cell. The project described in the paper has been used as a demonstration for junior- and senior-level undergraduate students in electrical engineering communications and optics classes.

ISSN:0002-9505    

DOI:10.1119/1.18683

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18686

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP