摘要:

The existence of light pressure and its magnitude are of great importance for the various 18th century theories about the physical nature of light. This paper examines the observations and experiments conducted in the 18th century to detect and measure this pressure. The reception of these results reveals another scientific strategy besides confirmation and refutation, namely, estimation of parameters. The author proposes the notion of primary evidence, for phenomena that are taken to confirm or refute theories, and problematic phenomena, for phenomena to which accepted theories are applied.

ISSN:0002-9505    

DOI:10.1119/1.1987899

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

The performance of college students in introductory physics courses has been studied using conventional examination procedures as a measure of content mastery. Retesting over the same physics content using repeatable equivalent examinations results in a significant increase in the students mastery of physics. Students greatly preferred this type of examination procedure.

ISSN:0002-9505    

DOI:10.1119/1.1987900

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

Several hundred students with backgrounds ranging from liberal arts to physics have successfully participated in basic research in The Pennsylvania State University Thermionic Emission Laboratory for the past five years. The value of this involvement to the students and other participants, and the factors leading to the success of the program are described and discussed.

ISSN:0002-9505    

DOI:10.1119/1.1987901

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

Many courses in physics are being developed for non-science majors. If the course is a success it should leave the students with an inquiring mind about the topics covered in class and about the constant discoveries and revisions being added to the mass of physical knowledge. But what courses have been designed with allocations for this type of progress? What alternatives should be available to a student who would like more than just an introductory course in the field of physics? This article proposes a plan that involves undergraduates in research, including undergraduates not majoring in physics. This plan could be incorporated into most universities and many colleges. It has been used at The Pennsylvania State University, where it has been enthusiastically endorsed by both students and faculty.

ISSN:0002-9505    

DOI:10.1119/1.1987902

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

A remote position measuring device with electrical coupling to a computer has been developed for use in the elementary-physics laboratory. Light from a moving object and a fixed-reference lamp is focused by a lens on a hollow, rotating drum with equally-spaced slits. The light passing through a slit is detected with a phototube. The time difference of amplified phototube signals from the object and reference-light sources is a measure of the position coordinate of the object at the time of the object signal. The model constructed has a precision of about 0.03 cm, better than a 3% differential linearity for a 40-cm field of view in the object plane and a sampling rate of30  sec−1.The device can track more than one object simultaneously and has been successful in providing position samples for two colliding gliders on an air-track.

ISSN:0002-9505    

DOI:10.1119/1.1987903

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

The quantum-mechanical energy-time uncertainty relation and the expression for the effect of a gravitational field on the rate of a clock are used in a simple demonstration that a quantum theory of gravitation must place a limit on the smallness of space-time intervals which can be measured.

ISSN:0002-9505    

DOI:10.1119/1.1987904

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

The classical cross section for scattering by a1/r2potential is linear in the strength of the potential, while from the Born approximation to quantum mechanics one might expect it to be quadratic. To resolve this puzzle, we explicitly carry out the passage to the classical limit of the quantum-mechanical partial-wave series for this potential. In the process, we discover the conditions under which quantum scattering becomes classical; under these conditions the Born approximation is not applicable.

ISSN:0002-9505    

DOI:10.1119/1.1987905

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

The variation of atmospheric refraction between the zenith distances 65° and 90° has been observed using a simple achromatic camera. A new formula gives the angle of refraction more accurately at large zenith distances than the familiar tangent ξ formula. The techniques used for camera calibration are also presented.

ISSN:0002-9505    

DOI:10.1119/1.1987906

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

It is pointed out that thep2forces of nuclear physics are structurally similar to the force postulated by Weber in pre-Maxwellian times to be acting between moving electric charges. A brief review of the essential features of the Weber force is accordingly presented, with particular emphasis being placed on the fact that although it is incorrect as a basis for electrodynamics it nevertheless leads to the correct expressions for the force and torque acting between closed circuits. It is in this way that we can understand the quasi-electromagnetic character of certain effects that arise in nuclear scattering in the presence of velocity-dependent forces.

ISSN:0002-9505    

DOI:10.1119/1.1987907

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP

摘要:

A method of dealing with charge conjugation and other discrete symmetries for Dirac particles is presented using a manifestly covariant notation which is simple to work with and which can be used in any representation of the Dirac matrices not explicitly involving the usual “B” and “C” matrices presented in many textbooks. Its use is illustrated by its application to discrete symmetries of the Dirac equation, field operators, and transition-matrix elements, and in defining phase conventions for spinors. The linear-versus-antilinear nature of charge conjugation is also discussed.

ISSN:0002-9505    

DOI:10.1119/1.1987908

出版商:American Association of Physics Teachers    

年代:1974

数据来源: AIP