ISSN:0002-9505    

DOI:10.1119/1.17711

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17649

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17653

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17654

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17655

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

The earliest prediction of the Sagnac effect, and of the possibility of detecting the Earth’s rotation with an interferometer of square kilometer area, is by Lodge (1893, 1897). We illustrate the extraordinary range of theoretical motivations for the experimental study of the Sagnac effect, starting with previously unpublished correspondence between Lodge and Larmor, and ending with present (and planned) ring interferometer experiments whose sensitivity to the Earth’s rotation is of the order of parts per million (billion, respectively).

ISSN:0002-9505    

DOI:10.1119/1.17656

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Does the Heisenberg uncertainty principle refer to errors of measurement, or to the spread of values of the physical variables intrinsic to a particle’s state, or to some combination of these? The most commonly quoted form of the uncertainty principle relates the spread of an ensemble of separate measurements of some variable to the analogous spread of its conjugate variable. In contrast, Heisenberg’s original argument for the uncertainty principle involved the perturbation to a particle’s state by a measurement of one variable, which affects one’s ability to predict the outcome of a subsequent measurement of the conjugate variable. The relation between these two views of the uncertainty principle is discussed in this paper. A familiar example is considered: an ensemble of identically prepared particles passing through a slit, and after further propagation being detected. From this arrangement it is possible to infer joint (although necessarily imprecise) information onbothtransverse position and conjugate momentum for each member of the ensemble. It is shown that in this case of joint measurement the product of standard deviations for the measurement outcomes is at least twice as large as the lower bound implied by the usual uncertainty principle. The discussion is meant to help clarify the different roles played in the various statements of the uncertainty principle by the initial state and by measurement error.

ISSN:0002-9505    

DOI:10.1119/1.17657

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

It is widely believed that measurement is accompanied by irreversible entropy increase. This conventional wisdom is based in part on Szilard’s 1929 study of entropy decrease in a thermodynamic system by intelligent intervention (i.e., a Maxwell’s demon) and Brillouin’s association of entropy with information. Bennett subsequently argued that informationacquisitionis not necessarily irreversible, but informationerasuremust be dissipative (Landauer’s principle). Inspired by the ensuing debate, we revisit the membrane model introduced by Szilard and find that it can illustrate and clarify (1) reversible measurement, (2) information storage, (3) decoupling of the memory from the system being measured, and (4) entropy increase associated with memory erasure and resetting.

ISSN:0002-9505    

DOI:10.1119/1.17749

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

The resistance between two adjacent nodes on an infinite square grid of equal resistors can easily be found by superposition. This paper addresses the corresponding problem for two arbitrary nodes. A solution is found by exploiting the symmetry of the grid and using the method of superposition. The mathematical problem involves the solution of an infinite set of linear, inhomogeneous difference equations which are solved by the method of separation of variables.  

ISSN:0002-9505    

DOI:10.1119/1.17696

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

The electric field on the axis of a slowly (v≪c) moving rectangular current loop is calculated using two concepts from introductory level physics textbooks; (1)Lorentz‐contractioninduced charge density, and (2)relativisticflatteningof the electric field pattern of a point charge moving with constant velocity. The correct field, proportional tovI/c2, on the axis of the moving loop is obtained only when both effects are considered and applied separately to the ions and electrons of the loop. Effect (1) is important only for the longitudinal sections of the loop, whereas effect (2) must be considered forallsections of the loop. The latter point is often overlooked in textbooks.  

ISSN:0002-9505    

DOI:10.1119/1.17697

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP