ISSN:0002-9505    

DOI:10.1119/1.17876

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17880

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18081

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17881

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17882

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17891

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

An undergraduate experiment is described in which the output of a noise generator is sampled by a computer equipped with a data acquisition board, after which the autocorrelation function is calculated. If the output of the noise generator passes through a low‐pass filter before it is sampled by the computer, then the autocorrelation function is a decreasing exponential function with a decay constant equal to the time constant of the low‐pass filter. The theory necessary to understand this phenomenon involves basic concepts in electrical noise, the analysis of linear systems, and Fourier transforms. In this paper the theoretical background for the experiment is discussed, typical data are presented, and a full analysis of these data is described.

ISSN:0002-9505    

DOI:10.1119/1.17892

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

About 1930, physicists were increasingly frustrated about the infinities of quantum electrodynamics and the strange behavior of what were believed to be nuclear electrons. As a way out of the problems Heisenberg suggested that space be subdivided in cells of finite size, and indicated in a letter to Bohr the essence of his theory. In Heisenberg’s lattice world, the electron could metamorphose into a proton, and the atomic nucleus consisted of protons and heavy ‘‘photons.’’ We analyze Heisenberg’s fascinating (but unpublished) theory in its historical context, and suggest a detailed reconstruction of the lattice world idea contained in the letter to Bohr.

ISSN:0002-9505    

DOI:10.1119/1.17848

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

The design and development of a new method for high school physics instruction is described. Students are actively engaged in understanding the physical world byconstructingandusingscientificmodelsto describe, explain, predict, and to control physical phenomena. Course content is organized around a small set of basic models. Instruction is organized intomodelingcycleswhich move students systematically through all phases of model development, evaluation, and application in concrete situations—thus developing skill and insight in the procedural aspects of scientific knowledge. Objective evidence shows that themodelingmethodcan produce much larger gains in student understanding than alternative methods of instruction. This reveals limitations of the popular ‘‘cooperative inquiry’’ and ‘‘learning cycle’’ methods. It is concluded that the effectiveness of physics instruction depends heavily on the pedagogical expertise of the teacher. The problem of cultivating such expertise among high school teachers is discussed at length, with specific recommendations for action within the physics community.

ISSN:0002-9505    

DOI:10.1119/1.17849

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Quantum field theory predicts a very large energy density for the vacuum, and this density should have large gravitational effects. However these effects are not observed, and the discrepancy between theory and observation is an incredible 120 orders of magnitude. There is no generally accepted explanation for this discrepancy, although numerous papers have been written about it. As usually stated the problem requires a knowledge of quantum field theory and general relativity, topics not normally studied by undergraduates. We have tried to make the problem accessible to undergraduates by using only the simplest ideas of quantum theory, such as the uncertainty principle and the theory of the harmonic oscillator, and classical gravitational theory. We believe that such simplification is not only an amusing pedagogical exercise but clarifies how basic is the conflict between quantum theory and gravitational theory. We do not here discuss various proposed solutions to the problem, beyond the trivial and unsatisfactory one of assuming an ad hoc canceling term in the Hamiltonian or field equations.

ISSN:0002-9505    

DOI:10.1119/1.17850

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP