ISSN:0002-9505    

DOI:10.1119/1.16186

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

This Resource Letter provides a comprehensive guide to the voluminous literature that has developed around Maxwell’s demon, and offers a perspective on issues for which the hypothetical character Maxwell introduced over 120 years ago has inspired continuing research and debate. The code (E) indicates elementary level or general interest material useful to persons just learning the field; (I) indicates intermediate level or somewhat specialized material; and (A) indicates advanced or highly specialized material. No accompanying AAPT reprint book will be available, because an extensive reprint collection (Ref. 29) edited by the authors will be published separately.

ISSN:0002-9505    

DOI:10.1119/1.16187

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

Feynman’s proof of the Maxwell equations, discovered in 1948 but never published, is here put on record, together with some editorial comments to put the proof into its historical context.

ISSN:0002-9505    

DOI:10.1119/1.16188

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A student experiment is described for studying persistent currents in a commercially obtained ring of the ‘‘123’’ superconducting material at liquid‐nitrogen temperature. The currents are easily detected with a standard analog Hall probe. From observations extended over a 3‐week period, an upper limit on the possible resistance of one such ring was set at about 2×10−16Ω. For the rings studied, the induced current saturated at about 2 A as the applied flux change was increased. An ac technique for checking the continuity of the superconducting path around the ring is also described. These experiments provide an interesting supplement for topics in first‐year electricity and magnetism. The effects are striking and easily discussed at an introductory level. For example, the current induced by turning the ring over in the Earth’s field is readily seen.

ISSN:0002-9505    

DOI:10.1119/1.16189

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

As the distinct scientific professions arose in the 19th century, the need for professional societies was felt. Spurred by the momentous discoveries of its last decade (x rays, radioactivity, the electron), the American Physical Society was organized in 1899. The initiative was taken by Arthur Gordon Webster; Rowland and Michelson, the most prestigious physicists in the country, accepted positions as president and vice president. The chief and almost exclusive concern of APS was the encouragement of research in pure physics. This single‐minded behavior resulted in the formation of other societies of physicists: the Optical Society of America in 1916, the Acoustical Society of America and the Society of Rheologists in 1929, and the American Association of Physics Teachers in 1930, with talk of associations for applied physics and mathematical physics. That fragmentation coupled with the financial difficulties of the APS led to the formation of the American Institute of Physics in 1931. AIP played a more active role during the war years than did APS, but after the war the Physical Society grew rapidly. Its 50th anniversary celebration, held at Harvard, was characterized by optimism despite the existence of many new problems.

ISSN:0002-9505    

DOI:10.1119/1.16190

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The variational method is applied to the problem of acxnpotential within an infinite one‐dimensional well. Approximate ground‐ and excited‐state wavefunctions are constructed as linear combinations of two‐term even and odd polynomials. Comparisons are made between calculated approximate wavefunctions and energies, and results predicted from perturbation theory and from the behavior of related systems.

ISSN:0002-9505    

DOI:10.1119/1.16488

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The physics of the forward motion of the flyline during a fly cast is discussed, and a computer model of this motion is proposed which reproduces the main features of this part of the cast.

ISSN:0002-9505    

DOI:10.1119/1.16191

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The Sears–Kestin statement represents a formulation of the second law of thermodynamics, restricted to adiabatic processes, which links equilibrium states and which is cyclic in the work variables (generalized displacements). Two conditions, formulated as axioms, are specified which, together with the Sears–Kestin statement, are necessary and sufficient to derive the Clausius inequality. Because these two additional axioms relate to reversible processes and to compound systems—general items not affecting the second law—the status of the Sears–Kestin statement among all the formulations of the second law is strengthened.

ISSN:0002-9505    

DOI:10.1119/1.16192

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A common laboratory experiment in radiative heat transfer involves measuring the cooling rate of two water‐filled metal cans, one can left unpainted and the other painted black. The shiny unpainted can cools more slowly, and the student can be led to the incorrect conclusion that bodies that are poor emitters (good reflectors) of light are also poor emitters of heat. A variation of this experiment was done with the shiny unpainted can replaced by one painted white. The experiment still compares a good and poor reflector of light, but in this case there is essentially no difference in cooling rates. These results are explained and are discussed in terms of other phenomena involving radiative heat transfer.

ISSN:0002-9505    

DOI:10.1119/1.16496

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

Of common interest to fighter pilots is what maneuver should be flown to accomplish a 360° heading change in the least time. Among the infinite possibilities, analytic expressions for a very commonly used maneuver, a roughly circular planar turn that accomplishes the required heading change, are derived and examined under four realistic assumptions. Contrary to common belief, the time to complete the stated heading change turns out to be independent of the inclination of the plane of the turn.

ISSN:0002-9505    

DOI:10.1119/1.16193

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP