ISSN:0002-9505    

DOI:10.1119/1.13655

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.13657

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.4755909

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.4755910

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The following is based upon a talk given at the American Physical Society Meeting in Baltimore, 18–21 April 1983 entitled, ‘‘Sakharov and Society’’ by Andrew M. Sessler. The occasion was the presentation by the Forum on Physics and Society of the 1982 Leo Szilard Award to Andrei Sakharov who was, of course, unable to attend. Dr. Sessler, former Director of the Lawrence Berkeley Laboratory, was Chairman, during 1982, of the American Physical Society Committee on the International Freedom of Scientists. Yvonne Howell is a freelance writer.

ISSN:0002-9505    

DOI:10.1119/1.13624

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The physical origin of the radiation force exerted by an ultrasonic beam on an absorbing target is explained. It is shown that the force may have two sources—a nonzero time‐averaged sound pressure in the ultrasonic beam, and the momentum transported by the beam—but that there is a movement of material out of the ultrasonic beam to prevent a nonzero time‐averaged sound pressure from being established. Consequently, the transfer of wave momentum is the sole cause of the force. The assumptions made in evolving this explanation are discussed, and the resulting change in mean density within the ultrasonic beam is considered. It is pointed out that the acoustic radiation force is but one example of a universal phenomenon associated with all forms of wave motion.

ISSN:0002-9505    

DOI:10.1119/1.13625

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

A student experiment is presented in which α‐particle time‐of‐flight measurements as well as direct α energy measurements are used to determine electronic stopping power parameters. For the time‐of‐flight measurements, α particles from a244Cm source are allowed to pass through a 14.6‐μm ΔEdetector, then a foil, and finally come to rest in anEdetector. The time‐of‐flight signals are obtained from the ΔEandEdetectors. The measured energies and velocities are then used to determine Bloch’s constant in the Bethe stopping power theory for Al, Cu, Ag, and Au. These student results are then compared to the theory. In order to show the feasibility of this technique for other measurements, a252Cf source is used to produce a fission fragment time‐of‐flight spectrum. The time resolution for the α group is 1.17 ns and that of the fission fragment light group is 1.68 ns.

ISSN:0002-9505    

DOI:10.1119/1.13626

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

Using only Newtonian gravity and a little special relativity we calculate most of the important effects of gravitational radiation, with results very close to the predictions of full general relativity theory. Used with care, this approach gives helpful back‐of‐the‐envelope derivations of important equations and estimates, and it can help to teach gravitational wave phenomena to undergraduates and others not expert in general relativity. We use it to derive the following: the quadrupole approximation for the amplitudehof gravitational waves; a simple upper bound onhin terms of the Newtonian gravitational field of the source; the energy flux in the waves, the luminosity of the source (called the ‘‘quadrupole formula’’), and the radiation reaction in the source; order‐of‐magnitude estimates for radiation from supernovae and binary star systems; and the rate of change of the orbital period of the binary pulsar system. Where our simple results differ from those of general relativity we quote the relativistic ones as well. We finish with a derivation of the principles of detecting gravitational waves, and we discuss the principal types of detectors under construction and the major limitations on their sensitivity.

ISSN:0002-9505    

DOI:10.1119/1.13627

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The constraints of classical mechanics are idealizations of stiff elastic forces. They can be derived from such forces in the limit of infinite stiffness, but this derivation presents some difficulties and the limit has to be taken carefully. In statistical mechanics it is no longer possible to idealize stiff potentials by constraints, not even approximately, except under a special and unrealistic restriction on the form of those elastic forces. In quantum mechanics the limit in general does not exist unless the same unrealistic condition is satisfied.

ISSN:0002-9505    

DOI:10.1119/1.13647

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

Compton scattering figures prominently in the introductory chapters of textbooks on quantum mechanics as providing evidence for the ‘‘particulate’’ nature of light. It also arises in discussions of ‘‘Heisenberg’s microscope,’’ in which it is shown that attempts to measure the position and the momentum of an electron simultaneously are governed by the uncertainty principle. However, recent developments in Compton scattering have not yet found their way into the textbooks. In this paper we review the history of the Compton effect and describe briefly some of the modern developments in x‐ray and electron Compton scattering and their application to the study of electron momentum densities which we believe to have a pedagogical value. Finally, we return to Heisenberg’s microscope, and show how it has now become a reality. A complete analysis for all scattering angles depends crucially on the different expressions for the resolution and the depth of focus of the microscope.

ISSN:0002-9505    

DOI:10.1119/1.13648

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP