摘要:

We attempt to determine the linear charge density on a finite straight segment of thin charged conducting wire. Several different methods are presented, but none yields entirely convincing results, and it appears that the problem itself may be ill‐posed.

ISSN:0002-9505    

DOI:10.1119/1.18236

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Electric fields produced by coplanar point charges have often been represented by field line diagrams that depict two‐dimensional slices of the three‐dimensional field. Serious problems with these ‘‘conventional’’ field line diagrams (CFLDs) have been overlooked. Two of these problems, ‘‘equatorial clumping’’ and ‘‘false monopole moment,’’ occur because a two‐dimensional slice lacks information vital to the accurate representation of an inherently three‐dimensional field. Equatorial clumping causes most CFLDs to exhibit unphysical behavior such as irregular spacing between field lines terminating on negative charges. CFLDs can also mistakenly indicate that a neutral charge distribution has a significant monopole moment. Such phenomena make the visual estimation of local field strengths impossible and render CFLDs of little utility for representing three‐dimensional fields. While these ‘‘projection’’ problems can be avoided by using two‐dimensional field line diagrams to represent two‐dimensional (1/r) electric fields, or by using three‐dimensional field line diagrams to represent three‐dimensional fields, other forms of distortion generally remain.

ISSN:0002-9505    

DOI:10.1119/1.18237

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The Faraday effect (the rotation of the plane of polarization of light as it propagates through a sample parallel to a static magnetic field) is readily detected in room‐temperature rubidium vapor by a diode‐laser experiment near theD2resonance line at 780 nm, and the theoretical treatment of this effect provides an unusually clear insight into the relation between absorption and dispersion in the interaction of light with matter.

ISSN:0002-9505    

DOI:10.1119/1.18356

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The correlation between potential shape and specific heat is generally absent from textbook discussions. We present a detailed analysis of the specific heat contribution due to independent particles subject to one‐dimensional classical and quantum model potentials. For the classical models, we use phase space concepts to develop a clear physical interpretation of the temperature dependence of the specific heat. For the quantum models, we make the interpretation in terms of the differences in quantum levels.

ISSN:0002-9505    

DOI:10.1119/1.18171

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

We describe the design, construction, and acoustical measurements of resonators with nonuniform cross‐sectional areas that are easily altered to yield different resonance frequencies. These resonators are useful as educational demonstrations of symmetry breaking and of an effect of nonuniformity upon standing waves. Resonators that yield two, three, and four pitches are considered, where the relative frequencies are designed to correspond to musical intervals. Agreement is within 2% in all cases and 1% for most. The data reveal a breakdown of the theory, which is shown to be a result of additional kinetic energy, and thus effective inertia, near a discontinuity in cross‐sectional area. The data also reveal that it is more accurate accurate to employ the end correction of an infinite flange rather than that of a thin‐walled tube.

ISSN:0002-9505    

DOI:10.1119/1.18172

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A simple experimental setup to produce true random numbers is described. The experiment involves measuring successive times between decays of a radioactive source. We discuss two different ways of comparing these times: one that generates a string of random zeros and ones, and another that produces numbers derivable from the permutation group. It is shown that the methods used in the experiment produce the same results for any random process and can therefore be used as a test for randomness in other physical systems.

ISSN:0002-9505    

DOI:10.1119/1.18173

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A simple apparatus employing a semiconductor diode laser and PIN photodiode has been used to investigate thermal capillary waves on liquid surfaces. These waves act as a weak, time‐varying diffraction grating for the incident laser light; the diffracted light can be heterodyned with the light directly reflected from the liquid surface to extract fluid properties (surface tension and viscosity). In this paper we present a discussion of the phenomenon of surface waves and describe the construction of an apparatus to observe them. Results of measurements with this apparatus for the surface tension and viscosity of water with and without oil films and of benzyl alcohol at different temperatures demonstrate the effectiveness of the technique as well as environmental effects on liquid properties. This problem provides rich ground for a study of wave and thermal phenomena as well as an introduction to a variety of experimental techniques.

ISSN:0002-9505    

DOI:10.1119/1.18174

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Nine of the 30 experiments performed by students in our 1‐year general physics laboratory involve computer‐assisted experimentation. Experiments are interfaced to the computer via conditioning circuits and an inexpensive 8 bit ADC/DAC card. Software is written for each experiment.

ISSN:0002-9505    

DOI:10.1119/1.18175

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

About a century before Young’s celebrated two‐slit experiment, Isaac Newton quantitatively investigated the diffraction of light from a wedge aperture, but failed to understand the implications of his findings. We have reexamined this unusual system theoretically within the framework of the Fresnel–Kirchhoff scalar diffraction theory, and experimentally using a laser light source with pinhole spatial filter and CCD camera. Both the far‐field shadow region and near‐field directly illuminated region reveal aesthetically striking images that are deducible from the mathematical analysis, but whose interpretation is subtle and best elucidated by an alternative and less widely known perspective of diffraction.

ISSN:0002-9505    

DOI:10.1119/1.18278

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Lifetimes of metastable levels of chromium in ruby are determined using an unusual technique. The fluorescence from the chromium is measured using an ac technique in which the excitation is modulated and the fluorescence is detected synchronously. The novelty lies in the measurement of the dependence of the signal on the modulation frequency and extracting the lifetime from the frequency dependence. The experiments and data analysis demand a detailed understanding of the methods of lock‐in amplification and synchronous detection and hence they can serve as a useful primer on the subject. The observed values for the lifetimes show excellent agreement with previous measurements.

ISSN:0002-9505    

DOI:10.1119/1.18176

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP