摘要:

A unified treatment of elementary surface phenomena based on the formalism of thermodynamics is presented and compared to more familiar treatments based on the formalism of Newtonian mechanics. Emphasis is put on the surface free energy concept rather than on surface tension, not only because the former is more fundamental, but also because the latter may mislead if pushed too far. The examples discussed (Young–Laplace and Young–Dupré equations, and capillary rise) can be easily described with the help of the Helmholtz function, and clearly show some of the advantages of the thermodynamic approach. In particular, several misleading results appearing in elementary treatments can be avoided by using this approach. It is concluded that: (i) thermodynamics and physical chemistry courses should favor the formalism of thermodynamics rather than mechanics when dealing with surface phenomena; and (ii) when the mechanical approach is still preferred, some weak points in the standard derivations (e.g., the existence of an adhesion force in the explanation of the Young–Dupré equation and the nature and balance of forces in capillary rise) should be properly dealt with.

ISSN:0002-9505    

DOI:10.1119/1.17866

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

In this paper we discuss our study of a string–mass chain and its anology to quantum mechanical systems. Theoretical predictions are made based upon the numerical solution to the wave equation. These predictions are tested experimentally using both normal mode analysis and pulse analysis. The frequency band structures for periodic and disordered string mass chains are studied as well as their corresponding eigenfunctions. The theoretical and experimental results are in accord. This experiment, suitable for advanced physics majors, demonstrates many important features of quantum mechanics: eigenvalues, superposition principle, band structure, gap modes, and Anderson localization.

ISSN:0002-9505    

DOI:10.1119/1.18089

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

We report the design and performance of a simple apparatus for measurement of shot‐noise fluctuations in the current from a vacuum photodiode illuminated with a pilot‐lamp light bulb. After calibrating the frequency‐dependent gain of the measurement electronics, the chargeeof the electron can be obtained by measuring the mean‐square shot noise as a function of the dc photodiode current. We employ op‐amp circuits and a rms‐to‐dc integrated circuit to amplify, filter, and detect the shot noise, so that commercial bandpass filters and rms voltmeters are unnecessary. The apparatus is therefore not expensive and can be built using readily available components. Repeated measurements employing different pilot lamps yield a value ofe=(1.581±0.015±0.032)×10−19C, where the uncertainties represent random (2σmean) and systematic error, respectively. The experiment thus permits reasonably precise measurements of a fundamental constant while allowing the undergraduate student to gain a hands‐on understanding of fluctuation phenomena.

ISSN:0002-9505    

DOI:10.1119/1.17867

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Coherent backscattering of light (CBS) is a phenomenon in which partial waves traversing time‐reversed (momentum‐reversed) scattering paths interfere constructively in the backscattering direction leading to the appearance of an intensity cone. This increase in reflectivity reduces the amount of light transported through the colloidal media. As an advanced undergraduate laboratory CBS introduces the student to low‐level light detection, precision angular resolved measurements, and sophisticated data analysis techniques. Additionally, the concept of photon self‐interference, usually discussed in Modern Physics class in the context of Young’s double slit experiment, is beautifully illustrated by CBS.

ISSN:0002-9505    

DOI:10.1119/1.17868

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

The duality relationship (α+2)(ᾱ+2)=4 between the power law potentials with powers α and ᾱ is studied for the limiting cases α→±∞, which correspond to a hard spherical well and to a hard sphere scattering problem respectively. The related power law potential approaches the inverse square potential.

ISSN:0002-9505    

DOI:10.1119/1.17869

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17870

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17871

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17872

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17874

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17875

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP