摘要:

Velocity-dependent potential functions can sometimes be used to determine the field of force that can be applied in order that particles may move in specified paths. In particular, the electromagnetic field vectorsEandBcan be determined from such a potential function if the paths on which charged particles move are specified.The velocity-dependent potentialUis related to the kinetic energyTand the Lagrangian functionLby the equationU = T − L, whereLis an arbitrary solution of the Lagrange equation(d/dt)(δL/δp′) − (δL/δp) = 0, wherep = constantrepresents the orthogonal trajectories of the curves which describe the paths the particles are to follow. From the velocity-dependent potential functionU, the field of force can be calculated by the definitionQp = −(δU/δp) + (d/dt)(δU/δp′).

ISSN:0002-9505    

DOI:10.1119/1.1933170

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

The number of physicists listed in the 1949 edition ofAmerican Men of Sciencewho have received their undergraduate degrees from various colleges and universities has been tabulated. For each institution the ratio of the number of listings in physics to the total enrollment has been computed. A comparison of these data with those available from previous editions suggests that universities having major graduate programs in physics are becoming increasingly important in the training of undergraduates.

ISSN:0002-9505    

DOI:10.1119/1.1933171

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

This article constitutes a report on an independent experimental study of the variation of the coefficient of sliding friction under very simple laboratory conditions. It is based on nonaccelerated motion involving sliding friction at speeds from 0.25 to 20 cm/sec. The experimental set-up consists of a weighted block resting upon a horizontal surface, subjected to the pull of various weights suspended over a pulley and attached to the block by means of a cord.For all materials tested, including wood, leather, glass, and various metals, it is found that (1) the coefficient of sliding friction varies as the logarithm of the speed of the moving surface, increasing directly as the logarithm of the speed increases, (2) in the case of wood surfaces in contact, the coefficient of sliding friction decreases as the normal force increases, (3) in the case of both wood and leather surfaces in contact with other surfaces, the coefficient decreases with repeated performance, and (4) in the case of metal surfaces in contact, the coefficient of friction increases with repeated performance, unless the product of the abrasive action of friction is removed for each performance. The removal of the loose metallic particles causes a decreased coefficient of friction.

ISSN:0002-9505    

DOI:10.1119/1.1933172

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

A new mechanism for rapidly absorbing the kinetic energy of the cart in Fletcher's apparatus is described, and experiments to determine the physical basis of its operation are discussed. It is shown that the energy is absorbed by viscous flow.

ISSN:0002-9505    

DOI:10.1119/1.1933173

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

A course is described dealing with the basic phenomena of radiation. Knowledge of differential equations is prerequisite. Since no appropriate textbook is available, more than thirty textbooks are mentioned from which a student may draw his material. Laboratory experiments are an important part of the course. Sources of material for these experiments are quoted.

ISSN:0002-9505    

DOI:10.1119/1.1933174

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

This is a brief review article on conductivity crystal counters in which their main properties and basic principles of operation are described. Their present position in the field of nuclear instrumentation is discussed, it being concluded that there are still many serious problems to be solved before the counters can be of practical use. Some of these problems and the present methods of tackling them are surveyed.

ISSN:0002-9505    

DOI:10.1119/1.1933175

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

When an emf, embedded in an electrically conducting medium, is measured by peripherally applied probe electrodes, the ratio of the measured potential drop to the total emf must be known. It is shown how this ratio can be obtained by computation. The specific case of an electromagnetic blood flow meter is used as the basis of computation.

ISSN:0002-9505    

DOI:10.1119/1.1933176

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

A solenoidal spectrometer is described. This instrument has several features which make it especially adaptable to use in an undergraduate laboratory. One is that the coil geometry is such that the student may readily verify that the range of variation of the magnetic field on the principal axis is less than14percent. Secondly, the baffle geometry is of sufficient simplicity to enable the better student to calculate not only the momentum admitted by the baffle system, but as well to predict the line shape for a monoenergetic source, and thus to obtain the theoretical resolution of the instrument. Thirdly, as a result of the first-mentioned features, the instrument is absolute. Construction details are included. For the instrument described, the absolute accuracy is better than 0.4 percent, the resolution is 1.9 percent, and the useful solid angle is 0.8 percent.

ISSN:0002-9505    

DOI:10.1119/1.1933177

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

摘要:

The decomposition of the stress tensor into the spherical stress tensor and the stress deviator found in theories of plasticity is shown to depend upon the postulate that the stress tensor is the tensor sum of two physically independent stress constituents. The decomposition is derived by two different methods, the first method based on energy arguments, and the second method based on cause and effect arguments.

ISSN:0002-9505    

DOI:10.1119/1.1933178

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.1933179

出版商:American Association of Physics Teachers    

年代:1952

数据来源: AIP