摘要:

An ohmic ring that rotates with constant angular velocity in an external uniform magnetic field is considered as a simple model for a current generator. Under the assumption that all quantities vary slowly in time, the lowest‐order approximation to the surface charge density is found. The flux of the Poynting vector through the loop surface is also computed. Unlike in the examples that are given in textbooks, this flux is not always incoming: It has the outgoing direction around the loop parts where the electrons are moving against electrostatic forces.

ISSN:0002-9505    

DOI:10.1119/1.18116

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

It is shown that the different patterns of blurriness observed on a photograph of a rolling bicycle wheel give a rather complete picture of the velocity field within a rolling disk.

ISSN:0002-9505    

DOI:10.1119/1.18117

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

As part of an upper‐level laboratory course, the oscillations of one and two mass systems on an airtrack were measured in real time. Both linear oscillations with spring forces and nonlinear oscillations with magnetic forces were analyzed with fast Fourier transforms and compared to theoretical predictions. The results for the coupled linear oscillator agree with the theoretical values to within 0.5%. The coupled nonlinear oscillator results were modeled numerically.

ISSN:0002-9505    

DOI:10.1119/1.18118

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A simple, direct, and inexpensive determination of the speed of sound in air, suitable for an undergraduate laboratory exercise, is presented. The same apparatus is used to demonstrate acoustic pulse reflections from closed and open ended tubes of circular cross section.

ISSN:0002-9505    

DOI:10.1119/1.18119

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Using a sequence of suitably chosen signals and interesting physical examples, Fourier analysis can be taught in an microcomputer based laboratory (MBL) with a minimum of mathematics. Thus, even nontrivial applications like the response of resonance circuits to δ‐function inputs can be treated on a very elementary level.

ISSN:0002-9505    

DOI:10.1119/1.18120

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A simple and didactical method is proposed to make evident the presence of the evanescent wave due to total reflection by introduction of an absorption factor in the optically less‐dense medium. The method permits taking precise quantitative measurements on the totally reflected beam and calculating the path length travelled by the evanescent wave in the optically less‐dense medium.

ISSN:0002-9505    

DOI:10.1119/1.18121

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A simple theory is proposed using Faraday’s law and the Lorentz force to analyze the effect of magnetic damping on an aluminum plate moving on a horizontal air track as it passes between the poles of a horseshoe magnet. The position, velocity, and acceleration of the nonmagnetic conducting plate are measured as a function of time using a motion detector. Using some simplifying assumptions, a theoretical model is obtained in which a single free parameter is used to fit the experimental data. This parameter corresponds to an effective length (LR) in which the eddy current encounters resistance as it moves around a closed path in the conductor. This leads to some interesting, but unexpected, results about the shape and magnitude of induced eddy currents.

ISSN:0002-9505    

DOI:10.1119/1.18122

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

We study the partial‐wave description of scattering of a particle from a one‐dimensional potential in quantum mechanics. There are two partial waves, with even and odd parity. They are decoupled if the potentialV(x) is symmetric, i.e.,V(x)=V(−x). IfV(x)≠V(−x), however, the two partial waves are coupled. This coupled‐channel problem can be handled in terms of two eigenphases and a mixing parameter. This method enables us to shed new light on the transmission and reflection probabilities at threshold.

ISSN:0002-9505    

DOI:10.1119/1.18123

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

White light was injected into a Michelson interferometer to obtain color fringes, which show a succession of dominant colors that we have analyzed quantitatively. For a given interferometric path length difference, ΔL, the resulting color fringe was sent to a diffraction grating spectrometer and light‐sensitive detector, to record its spectral composition. This data enabled us to depict the color in the two‐dimensional color space of thex–yC.I.E. chromaticity diagram. In this analysis, we show the dominant color in the progression of color fringes in interferometric color mixing to reverse the direction with which it sweeps through the visible spectrum, as ΔLis monotonically increased. This phenomenon is represented by spiraling with cusps and reversals of curvature in the C.I.E.x–yplane. Our measurements agree favorably with a theoretical model showing cusp behavior. We show the cusps to signify a transition from in‐ to out‐of‐phase behavior in the relative growth ofxandy. This result is robust, persisting for many trial spectral power distributions (SPDs) of the incident ‘‘white light’’ illuminant.

ISSN:0002-9505    

DOI:10.1119/1.18103

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A model of nonlinear oscillations is developed. The model decouples at once and nonlinear normal modes result. The solutions describe nonisochronous motion on invariant tori in phase space. Among the orbits there is a dense set on which the normal frequencies are in resonance. This oscillating system serves to illustrate many of the ideas of nonlinear dynamics, particularly the concept of integrability. The integrable system also provides the point of departure for an exploration of Hamiltonian chaos.

ISSN:0002-9505    

DOI:10.1119/1.18303

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP