摘要:

An exactly solvable model is presented that exhibits a phase transition and that can be exactly described by Landau's phase transition theory. The model is used to elucidate the constructs and assumptions that go into the Landau theory, and also to illustrate the role of fluctuations near an instability in a finite system.

ISSN:0002-9505    

DOI:10.1119/1.1986433

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

The Doppler broadening of gamma rays emitted during the motion of excited nuclei is measured with a high-resolution Ge(Li) detector. Results are interpreted in terms of the excited state lifetime and the processes by which the nuclei are brought to rest in condensed matter. While designed for a senior undergraduate laboratory, the experiment illustrates the principles involved in the various Doppler techniques currently used in nuclear lifetime studies and demonstrates the versatility of the Ge(Li) detector in applications other than direct energy or intensity measurement. The value55±10 fsecobtained for the lifetime of the 477-KeV state in7Liis in good agreement with values reported in the literature.

ISSN:0002-9505    

DOI:10.1119/1.1986434

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

During the decades immediately after its discovery, the Boyle-Mariotte gas law was formulated in terms of pneumatic “springs,” subsumed by Hooke under his own stress-strain relation, and generally regarded as a law of elasticity. The subsequent historical development of Boyle's principle, and that of the concept of elasticity with which it is no longer associated, provide thought-provoking test cases for Thomas Kuhn's notions of paradigm and puzzle solving in physics.

ISSN:0002-9505    

DOI:10.1119/1.1986435

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

A simple pictorial device, the intermolecular force triangleΔv,is introduced, which is capable of representing the structure and the physical content of the theory of intermolecular forces. The structure of the multipole expansion of the interaction potential energy, the first-order interaction energies arising from the interaction of the permanent moments of the interacting species, and the second-order induction and dispersion energies are discussed. Specific interactions are also considered that illustrate the usefulness of the intermolecular force triangle in predicting the various types of interaction energies that can arise in a given atomic or molecular collision.

ISSN:0002-9505    

DOI:10.1119/1.1986436

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

Two experiments were introduced in our senior modern physics laboratory to acquaint students with methods of doing complete experiments. In the “design” experiments, students individually chose, planned, designed, and listed all the apparatus, methods, and people required for a real experiment that might take several years to do. In the “ingenuity” experiments, students individually chose, planned, acquired, built, and assembled the apparatus for a relatively simple experiment and analyzed their measurements. We tested, by special laboratory examinations and other methods, if the half-class of students who had done these experiments were better than the half-class that had not.

ISSN:0002-9505    

DOI:10.1119/1.1986437

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

The effect of superradiance in the decay of coupled harmonic oscillators has been demonstrated in some simple experiments with two tuning forks and resonators. The results show the theoretically predicted shortening and lengthening of the decay times according as the oscillators are initially in phase or in antiphase. When the initial phase difference isπ/2,the decay times appear to be unaffected by the coupling of the oscillators.

ISSN:0002-9505    

DOI:10.1119/1.1986438

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

The question of whether to present the non-physics major with a direct current experiment beyond Ohms law and series and parallel laws has a pleasant solution. Construction of an analog computer for multiplication and division from common rheostats and student-assembled voltmeters leads to a firm grasp of basic series and parallel laws in d.c. circuits.

ISSN:0002-9505    

DOI:10.1119/1.1986442

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

The application of the thermodynamical law of mass action to the calculation of equilibrium conduction electron and hole concentrations in semiconductors is explained. The method can be applied to arbitrarily complicated systems of donors, traps, acceptors, etc., in addition to the intrinsic electron-hole excitation. The discussion is limited to small defect concentrations and quasifree charge carriers, so that the ideal-gas free energy and the Sackur-Tetrode entropy constant can be used. Exact solutions are straightforward but often so complicated that simplifying assumptions are useful. As an example the effect of compensation of donors is calculated as a function of temperature. The Fermi energy is simply related to the electron concentration.

ISSN:0002-9505    

DOI:10.1119/1.1986444

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

The electric field of a point charge moving at relativistic velocities along a single plane of motion may be visualized in a physically intuitive way with the aid of pictures of the electric lines of force. A general derivation of exact parametric equations for these lines of force is described and applied to create the pictures presented here of synchrotron radiation, low-angle high-energy Coulomb scattering, abrupt linear acceleration of a charge, and a charge undergoing simple harmonic motion.

ISSN:0002-9505    

DOI:10.1119/1.1986445

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP

摘要:

It is pointed out that accounts in the literature sometimes misinterpret the Aharonov-Bohm effect, involving the shift in interference pattern for electrons passing a long solenoid. The quantum description and experimental verification of the effect are reviewed, and it is emphasized that both theory and experiment indicate that there is no deflection of the average momentum of the electrons passing the solenoid. There is no average force on the electrons due to the solenoid. It is remarked that the Aharonov-Bohm effect involves the shift of double-slit interference fringes which is independent of the quantum unit of action ħ and yet allows a natural classical limit.

ISSN:0002-9505    

DOI:10.1119/1.1986446

出版商:American Association of Physics Teachers    

年代:1972

数据来源: AIP