ISSN:0002-9505    

DOI:10.1119/1.18554

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

This paper describes experiments performed by undergraduate physics majors to measure the temperature dependence of Doppler-broadening in Rb absorption lines over the interval 290–500 K. We report measurements made with a laser-diode spectrometer on the resolved hyperfine transitions of87Rb(5 2S1/2F=1to5 2P1/2,F=1and 2) near 795 nm, and on the unresolved envelope of the transitions of85Rb(5 2S1/2F=2to5 2P3/2,F=1, 2 and 3) near 780 nm. Agreement between measured and predicted linewidths is very good.

ISSN:0002-9505    

DOI:10.1119/1.18553

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

We present a laboratory experiment designed to show the main characteristics of blue light-emitting diodes. The analyzed devices are based on III–V nitrides (in which the active layer is a direct band gap In0.06Ga0.94N alloy) and SiC (where the active layer is the 6H polytype of this semiconductor, which is of an indirect band gap class). From the measurements, anInrelation could be established between light emission and device current, withnvalues related to both the physical structure and electroluminescence characteristics of these semiconductors. The spectral response measurements allow us to obtain the peak wavelength of emission with reasonable precision (449±4 nm in the former one and 470±4 nm in the last one). It is also possible to accurately obtain the band gap value of the active layer in the device based on III–V nitrides (3.18±0.03 eV) by analyzing its electroluminescence spectra. However, the same analysis is not possible in the SiC-based device due to its extremely low measured luminous intensity values. A comparison of power conversion efficiency of both devices is also given.

ISSN:0002-9505    

DOI:10.1119/1.18547

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

The inverted plane pendulum is re-examined for the cases of horizontal or vertical driving of the pivot by a harmonic force, with principal interest in the computer simulation of the ensuing motions. While the regions of parameter values for which the vertically driven inverted motion is stable are well understood, and numerical simulation itself is quite stable, the situation is not as clear for the case of horizontal driving. We investigate the origins of these differences from the vertically driven case and resolve them. In doing so, some little-known modes of the horizontally driven hanging pendulum are uncovered and some of their properties are discussed.

ISSN:0002-9505    

DOI:10.1119/1.18774

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

We study the Casimir force between a perfectly conducting and an infinitely permeable plate with the radiation pressure approach, used by earlier authors for the case of two perfectly conducting plates. This method illustrates in a very simple context how a repulsive force arises as a consequence of the redistribution of the vacuum-field modes corresponding to specific boundary conditions. We show that the result is independent of the cutoff function used for regularization.

ISSN:0002-9505    

DOI:10.1119/1.18548

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

We present an approach to two-body collision processes which simplifies the algebra and leads to a convenient geometrical visualization of these processes in the velocity plane. Special cases, such as the lab and center-of-mass frames, can easily be extracted from the general solutions without further algebra. The geometric interpretation provides insight into the dynamics of collisions without having to consider numerous special cases. Thus important physics concepts can be illustrated without students becoming lost in the algebra.

ISSN:0002-9505    

DOI:10.1119/1.18549

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

The simple harmonic oscillator plays a prominent role in most undergraduate quantum mechanics courses. The study of this system using path integrals can serve to introduce a formulation of quantum mechanics which is usually considered beyond the scope of most undergraduate courses. However, given the current interest in the interpretation and foundations of quantum mechanics, nonstandard approaches such as Feynman’s path integral formalism can be helpful in developing insights into the structure of quantum mechanics. In this paper we evaluate the path integration appearing in Feynman’s treatment in a natural and direct manner utilizing a symbolic computational program. This approach makes the use of the path integral formulation of quantum mechanics accessible to most undergraduate physics majors. As a by-product of our approach, we find a representation of the reciprocal of the sinc function, sinc (x)≡sin(x)/(x), in terms of an infinite product of partial approximates of a continued fraction. We have not found this representation in the literature.

ISSN:0002-9505    

DOI:10.1119/1.18545

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

The dynamics of a sinusoidally driven pendulum in a repulsive magnetic field is investigated theoretically and experimentally. The experimental data are acquired using a shaft encoder interfaced to a PC which measures the angular displacement of the pendulum as a function of time. Both the theoretical simulations and the experimental measurements exhibit regions of periodic and chaotic behavior, depending on the system parameters. Amplitude jumps, hysteresis, and bistable states are also observed. The simplicity of the apparatus makes this experiment suitable for an advanced undergraduate laboratory.

ISSN:0002-9505    

DOI:10.1119/1.18546

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

It is shown that the operator methods of supersymmetric quantum mechanics and the concept of shape invariance can profitably be used to derive properties of spherical harmonics in a simple way. The same operator techniques can also be applied to several problems with noncentral vector and scalar potentials. As examples, we analyze the bound state spectra of an electron in a Coulomb plus an Aharonov–Bohm field and/or in the magnetic field of a Dirac monopole.

ISSN:0002-9505    

DOI:10.1119/1.18551

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP

摘要:

The barometric formula, relating the pressurep(z)of an isothermal, ideal gas of molecular massmat some heightzto its pressurep(0) at heightz=0, is discussed. After a brief historical review, several derivations are given. Generalizations of the barometric formula for a nonuniform gravitational field and for a vertical temperature gradient are also presented.

ISSN:0002-9505    

DOI:10.1119/1.18555

出版商:American Association of Physics Teachers    

年代:1997

数据来源: AIP