ISSN:0002-9505    

DOI:10.1119/1.18474

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18109

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The quantum mechanical description of reflection and refraction in terms of photons is further extrapolated. The probability amplitude for a photon to be found inside or outside the medium is derived.

ISSN:0002-9505    

DOI:10.1119/1.18465

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The positrons from β+decaying sources loss energyat a much faster rate than they annihilate. As the energy of the positrons drops, core excitations, plasmon excitation, electron/hole pair creation, and phonon scattering are the dominant processes of further energy loss.

ISSN:0002-9505    

DOI:10.1119/1.18105

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18106

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The following article is a written version of the Richtmyer award lecture given to the annual meeting of the American Association of Physics Teachers in January 1996. I discuss the basic idea of Bose–Einstein condensation in a gas and how it has been produced and examined. To cool the atoms to the point of condensation we use laser cooling and trapping, followed by magnetic trapping and evaporative cooling. These techniques are explained, along with the signatures of Bose–Einstein condensation that we observe. I also discuss how very similar laser cooling and trapping techniques have been incorporated into undergraduate laboratory experiments.

ISSN:0002-9505    

DOI:10.1119/1.18111

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The significance of the surface electric charge densities associated with current‐carrying circuits is often not appreciated. In general, the conductors of a current‐carrying circuit must have nonuniform surface charge densities on them (1) to maintain the potential around the circuit, (2) to provide the electric field in the space outside the conductors, and (3) to assure the confined flow of current. The surface charges and associated electric field can vary greatly, depending on the location and orientation of other parts of the circuit. We illustrate these ideas with a circuit consisting of a resistor and a battery connected by wires and other conductors, in a geometry that permits solution with a Fourier–Bessel series, while giving flexibility in choice of wire and resistor sizes and location of the battery. Plots of the Poynting vector graphically demonstrate energy flow from the battery to the resistive elements. For a resistor with a large resistance, the potentials and surface charge densities around the current‐carrying circuit are nearly the same as for the open circuit with the resistor removed. For such resistors, the capacitance of a resistor and its adjacent elements, defined in terms of the surface and interface charges present while current flows, is roughly the same as the capacitance of the adjacent elements of the open circuit alone. The discussion is in terms of time‐independent currents and voltages, but applies also to low‐frequency ac circuits.

ISSN:0002-9505    

DOI:10.1119/1.18112

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The elements of the Dirac algebra are represented by sixteen 4×4 gamma matrices, each pair of which either commute or anticommute. This paper demonstrates a correspondence between the gamma matrices and the complete graph on six points, a correspondence that provides a visual picture of the structure of the Dirac algebra. The graph shows all commutation and anticommutation relations, and can be used to illustrate the structure of subalgebras and equivalence classes and the effect of similarity transformations. Since gamma matrices are the direct products of two Pauli spin matrices, they provide an appropriate way to describe a system of two spin‐1/2 particles. Such multiparticle spin states are intimately connected with the theorems of John Bell. The graph is helpful in analyzing an important example of the Bell–Kochen–Specker theorem.

ISSN:0002-9505    

DOI:10.1119/1.18113

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

R. P. Feynman’s ‘‘path integral’’ approach to quantum field theory emerged from his discovery that the Schrödinger equation could be derived from an expression of P. A. M. Dirac’s involving the action. Feynman gave the history of his discovery in his Nobel lecture, but withheld most of the details; when he did publish the discovery, he did not provide the framework. This article provides some historical background and puts both of Feynman’s presentations together.

ISSN:0002-9505    

DOI:10.1119/1.18114

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The development of a mechanical, damped, forced, harmonic oscillator system with computer data acquisition and analysis was undertaken. The original aim was to make accurate comparisons of experimental data with the standard textbook analyses, especially with regard to the phase difference between the displacement response and the driving force, and to the functional form of the displacement response versus frequency curve. Accurate measurements of the phase and amplitude for the displacement responses for the system developed indicated that for real systems with damping, the conventional analysis needs to be revised. If electromagnetic damping is used, the effective restoring forces must include the electromagnetic forces resulting from the interaction of the ‘‘eddy’’ currents with the damping magnetic field, and this can be considered as increasing the effective spring constant. When viscous damping is used, fluid adhering to the damping system changes the effective oscillating mass. Both of these effects will change the resonant frequency. Experimental data and analysis are presented to confirm the revised theoretical treatment.

ISSN:0002-9505    

DOI:10.1119/1.18115

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP