ISSN:0002-9505    

DOI:10.1119/1.17397

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

When two magnetic monopole distributions interact, the forces are conservative, and mechanical work is transformed into energy stored in the field, as in electrostatics. However, if a monopole distribution interacts with an electric current distribution, the forces are nonconservative; external work done on a monopole system appears as kinetic energy of the moving electric charges. In this case the magnetic field energy does not change in first order, during a displacement or reorientation of one system relative to the other. Contributions to the energies of interaction are calculated and compared for various combinations of magnetic systems. ‘‘Monopole threading’’ effects are also described, which affect the kinetic energy within an electric current loop when a monopole passes through it.

ISSN:0002-9505    

DOI:10.1119/1.17398

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

The hyperfine contact interaction is examined for a nuclear magnetic dipole moment of polar origin, due to separated monopoles of opposite sign. In the ground state of hydrogen, where the electron distribution overlaps the nucleus, an electron‐nucleus interaction of the form −μN⋅Beleads to hyperfine level shifts in agreement with experiment and in disagreement (by a factor of −2) with calculations based on −μe⋅BN. The latter are brought into accord with experiment by a ‘‘monopole threading’’ contribution arising from the passage of a monopole through the surface bounded by a circulating electric current. Measurements of the 1 s hyperfine splitting in hydrogen apparently do not test for monopole‐pair contributions to nuclear magnetism.

ISSN:0002-9505    

DOI:10.1119/1.17399

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

Cosmological horizons play an essential role in determining the causal structure of spacetime and are of central importance in the inflationary universe scenario. We review the topic of horizons in simple language, pointing out a number of widespread misconceptions. The use of spacetime diagrams plotted in terms of proper time and proper distance coordinates helps sort out some of these difficulties. They complement the widely used conformal diagrams, which show causal relations clearly but severely distort proper distances.

ISSN:0002-9505    

DOI:10.1119/1.17400

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

A solution to the paradoxical problem of a square wheel is presented. Using kinematics, it is shown that the correct roadbed for a square object rolling without slipping is a series of inverted catenaries. The dynamics of the square are revealed by the conservation of energy method. Remarkably, the square is shown to be capable of winning a downhill race against a sphere on a parallel inclined plane.

ISSN:0002-9505    

DOI:10.1119/1.17401

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

Equipment designed for the absolute measurement of voltage is described, suitable for lecture demonstrations or for student laboratory experiments. Although simple and inexpensive it can give results accurate to 1% or 2%. A key element incorporated is a soft drink can.

ISSN:0002-9505    

DOI:10.1119/1.17359

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

Construct a polygon of equal resistors,R, and also connect each vertex to the center with resistanceR. It is shown that for a large number of sides,N, the entire network of 2Nresistors has a vertex‐to‐center resistance ofR/√5. The convergence of the sequence with increasingNis related to the Fibonacci sequence.

ISSN:0002-9505    

DOI:10.1119/1.17360

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

Two of the most common terms employed in discussing cosmological models areopenandclosed. They are occasionally misused either by not recognizing or by not making it clear that each term may be used to characterize,independentlyandsimultaneously, both the dynamic behavior and spatial geometric structure of the model under discussion. In addition, the spatial geometric structure implied by the termsopenandclosedis itself often either misunderstood or misused. Lastly, the role played by the cosmological constant is often improperly slighted. This paper is intended to give several examples of the abuse of terminology and clarify the distinction by means of a brief, elementary overview of Friedmann–Robertson–Walker cosmological models.

ISSN:0002-9505    

DOI:10.1119/1.17361

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

We show that the presently accepted standard model of the Sun exhibits polytropic power‐law behaviorP=Kργover certain regions of the Sun’s interior. We then develop a three‐polytype model that gives a good representation of this standard solar model. The model is easily computable.

ISSN:0002-9505    

DOI:10.1119/1.17362

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP

摘要:

The set of feasible operations of a finite‐time heat engine subject only to thermal losses is described in terms of a new inequality, which sets alowerbound for the time required by a Carnot‐like process in terms of the entropy changes of the reservoirs. This leads to an analogue of the second law of thermodynamics and to a general notion of time efficiency for the class of processes considered.

ISSN:0002-9505    

DOI:10.1119/1.17363

出版商:American Association of Physics Teachers    

年代:1993

数据来源: AIP