ISSN:0002-9505    

DOI:10.1119/1.16267

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

In the ‘‘hot chocolate effect’’ the best musical scales (those with the finest tone quality, largest range, and best tempo) are obtained by adding salt to a glass of hot water supersaturated with air. Good scales can also be obtained by adding salt to a glass of freshly opened beer (supersaturated with CO2) provided you first (a) get rid of much of the excess CO2so as to produce smaller, hence slower, rising bubbles, and (b) get rid of the head of foam, which damps the standing wave and ruins the tone quality. Finally the old question, ‘‘Do ionizing particles produce bubbles in fresh beer?’’ is answered experimentally.

ISSN:0002-9505    

DOI:10.1119/1.16268

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

It is a commonly accepted myth that Marie Curie and Lise Meitner were the only women working in the field of nuclear science during the early part of this century. In fact, there were at least 14 others who published work in this field between 1900 and 1915. This paper provides biographical notes on these women and explores the role of the supervisors. Part of the reason for the significant number of women researchers could have been the supportive attitude of Ernest Rutherford toward female physics graduates. In addition, we argue that several of these women provide better role models for potential women physicists than Marie Curie.

ISSN:0002-9505    

DOI:10.1119/1.16269

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A physical explanation for group velocity is given for the very common case of group velocity less than the phase velocity with negligible absorption. The underlying physics is that a nonpropagating or immobilized energy density must be present in the medium associated with the presence of the wave field. The individual waves carry energy forward in a wave packet and energize the medium in the forward portion of the packet. In the rear portion of the packet, the individual waves grow at the expense of the energy immobilized in the medium, the particle motions in the medium being in phase with the wave field and therefore capable of generating new waves in phase with the group of waves that produced them. The physics is conveniently described in terms of deep water waves, but the principles involved apply equally well to other dispersive, nonabsorbing media, including plasmas, dielectrics, and waveguides. The flux of energy can be expressed as the phase velocity times that part of the energy density that propagates with the individual waves or, averaged over a wave period, as the total energy density (including the energy immobilized in the medium) times the group velocity. This eliminates the confusion commonly present when an attempt is made to interpret the Poynting flux for electromagnetic waves in terms of the product of an energy density and the group velocity. The group velocity is just the weighted average velocity.

ISSN:0002-9505    

DOI:10.1119/1.16270

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A novel method for circuit analysis is presented, which can help in the development of intuition about the current distribution in a complicated circuit with an emf source and resistors, and can be used for analytic and numerical calculations.

ISSN:0002-9505    

DOI:10.1119/1.16490

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

An apparatus is described for the measurement of the group velocity of light in transparent media. The apparatus uses a modified He–Ne laser as a stable, amplitude‐modulated light source. With the aid of a single beam oscilloscope, results for the velocity of light in air accurate to ∼0.02% have been obtained. This accuracy is sufficient to enable the relationship between the group and phase velocities in transparent dispersive media to be experimentally verified.

ISSN:0002-9505    

DOI:10.1119/1.16271

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

This article attempts to clarify the role of the magnetic force and the ‘‘rotational’’ component of the electric field in calculating the induced electromotive force in a circuit having a moving part. For this purpose, an example where both terms occur is analyzed.

ISSN:0002-9505    

DOI:10.1119/1.16272

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

This paper describes several relativistic phenomena in two spatial dimensions that can be modeled using thecollisionprogram of Spacetime Software. These include the familiar aberration, the Doppler effect, the headlight effect, and the invariance of the speed of light in vacuum, in addition to the rather unfamiliar effects like the dragging of light in a moving medium, reflection at moving mirrors, Wigner rotation of noncommuting boosts, and relativistic rotation of shrinking and expanding rods. All these phenomena are exhibited by tracings of composite computer printouts of thecollisionmovie. It is concluded that an interactive educational graphics software with pleasing visuals can have considerable investigative power packed within it.

ISSN:0002-9505    

DOI:10.1119/1.16273

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

This article discusses the microcomputer simulation of dynamical systems that have a few degrees of freedom but which illustrate the properties associated with ergodicity and mixing shared by more realistic many‐particle systems. The models discussed are a stadium‐shaped billiard table model, and a particle moving in a regular array of hard disks or two‐dimensional Lennard–Jones particles. The examples show the need for a statistical description and are very useful for pedagogical purposes.

ISSN:0002-9505    

DOI:10.1119/1.16274

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A nuclear experiment has been designed for use in the undergraduate laboratory. Following a theoretical treatment of alpha barrier penetration and the kinematics andQvalue of alpha decay, a semiclassical calculation is made for the half‐life for alpha decay, followed by a more exact quantum mechanical result. The decay schemes of three commercially available sources are studied. The branching ratios to various excited states in the residual nuclei are measured along with the precise energies of the decay. The absolute activity of one source (241Am) is determined from its measured alpha activity, and from its gamma activity as measured by a low‐energy photon detector.

ISSN:0002-9505    

DOI:10.1119/1.16275

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP