ISSN:0002-9505    

DOI:10.1119/1.16502

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16369

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A simple method of measuring the charge induced on a conductor is presented. The method is based on the idea that a charged projectile passing near a conducting object will cause surface charges to be dynamically induced on its surface. By suitably arranging a detector in the surface of the object, the charge drawn onto the conductor during the passage of the charged projectile can be measured and related to the induced surface charge density. The charge is computed by integrating the current waveform. The concept has been used to design a detector that measures the charge induced on a high‐speed projectile such as a pellet fired from an air rifle, the charge induced on a raised hemispherical boss by a uniform electric field, and the surface charge induced on a flat plate by a point charge.

ISSN:0002-9505    

DOI:10.1119/1.16371

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

In an effort to discover what makes the humanities difficult and unpopular with some science and engineering students, 14 Cornell faculty from the disciplines of chemistry, physics, applied mathematics, geology, materials science, and engineering were invited to become ‘‘surrogate learners’’ in a junior/senior level poetry seminar designed expressly for them. Their encounter with humanistic pedagogy and scholarship was meant to be an extension of ‘‘Peer Perspectives on Science’’ [see S. Tobias and R. R. Hake, ‘‘Professors as physics students: What can they teach us?’’ Am. J. Phys.56, 786 (1988)]. The results challenge certain assumptions about differences between scholarship and pedagogy in the humanities and science (as regards ‘‘certainty’’ and models). But the experiment uncovered other problems that affect ‘‘marketing’’ the humanities to science and engineering students. Results are some additional insights into what makes science ‘‘hard’’ for humanities students and why physical science and engineering students have difficulty with and tend to avoid courses in literature, as well as into what can make humanities courses valuable for science students.

ISSN:0002-9505    

DOI:10.1119/1.16372

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The twin paradox of special relativity results from failing to recognize the fundamental asymmetry between the two twins: One and only one twin changes direction and thus undergoes acceleration. What happens if the universe is closed, so that the twin in the rocket can return to Earthwithoutchanging direction? The twin paradox is reformulated in a closed universe (a cylinder) and then resolved by showing that there is still a (much more subtle!) asymmetry between the two twins.

ISSN:0002-9505    

DOI:10.1119/1.16373

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The Bohr–Einstein debate over the ‘‘weighing of energy’’ and the validity of the time–energy uncertainty relation is reexamined in the context of gravitation theories that do not respect the equivalence principle. Bohr’s use of the equivalence principle is shown to be sufficient, but not necessary, to establish the validity of this uncertainty relation in Einstein’s ‘‘weighing‐of‐energy’’ gedanken experiment. The uncertainty relation is shown to hold in any energy‐conserving theory of gravity, and so a failure of the equivalence principle does not engender a failure of quantum mechanics. The relationship between the gravitational redshift and the equivalence principle is reviewed.

ISSN:0002-9505    

DOI:10.1119/1.16374

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A distinction is made between the ‘‘popular many‐worlds interpretation’’ and Everett’s ‘‘relative state’’ formulation of quantum mechanics. This distinction is claimed to be relevant to arguments raised against both schemes.

ISSN:0002-9505    

DOI:10.1119/1.16375

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

If its radius of gyration is properly tuned, a mass attached to a simple helical spring is able to perform longitudinal and torsional oscillations that are coupled with one another and exhibit the beats characteristic to coupled oscillations. The mechanism of coupling as well as the corresponding differential equations are derived. For the case of resonance, the solutions are compared with experimental results.

ISSN:0002-9505    

DOI:10.1119/1.16376

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The small oscillations of a parallelepidal magnet along the axis of a circular coil carrying an electric current have been analyzed theoretically and experimentally. The study of this system (a particular case of a magnetic dipole in motion in a nonuniform magnetic field) involves basic ideas from both mechanics and electromagnetism, and the equipment used in the experiment is very common in an undergraduate laboratory. Comparison with the experiment shows that a very simple theoretical approach gives good results. It is also shown how the introduction of some refinements in the physical model can improve the agreement between theory and experiment, though the theoretical analysis becomes more involved in this case. The use of the principle of superposition to calculate magnetic fields is emphasized throughout the article.

ISSN:0002-9505    

DOI:10.1119/1.16377

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A method to show the temporal evolution of wavefunctions in linear lossless media is developed by using the inverse fast Fourier transform. Sequential images of the wave patterns are obtained by assuming simple phase functions for different dispersion relations, and for any given kind of spectra. The evolution of a wave packet shows the different group and phase velocities, and the deformation and spreading of the envelope in several dispersive media.

ISSN:0002-9505    

DOI:10.1119/1.16347

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP