摘要:

A Josephson junction, consisting of two superconductors weakly coupled together, is an example of a very simple macroscopic quantum system. When there is a voltageVacross the junction, the supercurrents flowing through it oscillate at a frequency given very precisely by the relationv = 2eV/h. The general validity of this formula has been used recently by Parker, Langenberg, Denenstein, and Taylor as the basis for a new determination of the fundamental constant ratioe/h. The new value is38±10ppm smaller than the previously accepted value. This result has far-reaching implications concerning the values of the fundamental constants and quantum electrodynamics. This article begins with a simple derivation of the Josephson voltage-frequency relation. Theory suggests that there should be no significant corrections to this equation, a result which is well confirmed by experiment. Various types of junction are then described, together with their applications to the measurement ofe/h. The impact of this measurement upon the fundamental constants and quantum electrodynamics is briefly discussed. It seems likely that Josephson junctions will have an important application in comparing and maintaining standards of electromotive force.

ISSN:0002-9505    

DOI:10.1119/1.1976556

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

An advanced laboratory experiment of Fresnel diffraction is presented. A He-Ne gas laser is used as the source and a wire is used as the opaque diffracting strip. A photograph of the diffraction pattern is compared with the intensity diagram predicted by the Cornu spiral method. Agreement is clear and impressive, although minor differences are detectable.

ISSN:0002-9505    

DOI:10.1119/1.1976557

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

The state representative for a composite system cannot be uniquely reconstituted solely from knowledge of the state of the constituents. Spin and angular momentum examples are used to illustrate this behavior. The need and motivation for holistic principles to allow the determination of a single state is discussed.

ISSN:0002-9505    

DOI:10.1119/1.1976558

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

An introductory physics laboratory concerned with scattering particles off various force centers is reported. The experiment uses simulation techniques and a computer. The scattering is classical, and the student examines plots of computed particle trajectories. The results illustrate the concepts of differential cross section, total cross section, and effective potential. Introductory students understand the calculational method geared to the computer. The response of both students and faculty has been very positive.

ISSN:0002-9505    

DOI:10.1119/1.1976559

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

An interesting extension to the conventional Doppler shift experiment is described. The basic equipment is similar to other X-band systems and is built around a 4-port directional coupler. By using a vibrating mirror in place of the normal constant velocity reflector, the output from the mixer can be observed to occur at both the expected Doppler frequency and at double this frequency, depending on the position of the mirror. This rather surprising result is discussed in terms of a pseudo-standing-wave model and also in terms of mixing the Doppler shifted frequency with the transmitted frequency.

ISSN:0002-9505    

DOI:10.1119/1.1976560

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

It is shown that, contrary claims notwithstanding, apparently no one before Einstein in 1905 ventured the idea that all clocks in motion might go slow. And thus, however logical it would have been, there never existed a theory based on the axioms of length contraction and time dilation relative to the ether.

ISSN:0002-9505    

DOI:10.1119/1.1976561

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

A double pendulum apparatus is described, with which a great variety of figures similar to Lissajous figures can be drawn. This apparatus has great appeal to users of all sorts. In addition to the use of this apparatus for drawing figures, several more advanced physical subjects can be studied with the aid of this instrument.

ISSN:0002-9505    

DOI:10.1119/1.1976562

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

The introductory physics laboratory is examined historially and philosophically. The rationale for the introductory laboratory is established with criteria for improvements.

ISSN:0002-9505    

DOI:10.1119/1.1976563

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

To gain insight into some biological processes in which a subsystem becomes ordered while gaining energy, an extremely simple physical process having these characteristics is analyzed. Each cycle of the process considered is formally the same as the description of the dynamic polarization of nuclei (Overhauser effect). In the biological process a crucial role is played by an “organizer,” a physical system which puts the subsystem of interest into improbable high-energy states. The role of the organizer, a close relative to the Maxwell demon, is played by the electron spin in the Overhauser effect. The role of feedback is investigated and relaxation times are evaluated in the Appendix.

ISSN:0002-9505    

DOI:10.1119/1.1976564

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP

摘要:

It is shown in this paper that analog computer simulation can be used as a convenient tool to demonstrate visually some fundamental properties of plasma physics. In this study, it is also observed that a new plasma drift mechanism exists in a nonstatic anisotropic plasma.

ISSN:0002-9505    

DOI:10.1119/1.1976565

出版商:American Association of Physics Teachers    

年代:1970

数据来源: AIP