ISSN:0002-9505    

DOI:10.1119/1.16858

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16859

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

A novel demonstration of chaos in the double pendulum is discussed. Experiments to evaluate the sensitive dependence on initial conditions of the motion of the double pendulum are described. For typical initial conditions, the proposed experiment exhibits a growth of uncertainties which is exponential with exponent λ=7.5±1.5 s−1. Numerical simulations performed on an idealized model give good agreement, with the value λ=7.9±0.4 s−1. The exponents are positive, as expected for a chaotic system.

ISSN:0002-9505    

DOI:10.1119/1.16860

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

The tunneling probability for majority carriers in an ohmic contact ton‐type GaAs has been calculated by directly solving the Schrödinger equation for the wave functions in the semiconductor depletion region. The direct solution is straightforward and relies on fewer assumptions than previous calculations based on the WKB approximation. It also provides a useful application of undergraduate quantum mechanics to an important area of VLSI semiconductor technology. The direct solution can be performed on an 80286 machine in less than a minute and yields tunneling probabilities roughly twice as large as the WKB approximation at most electron energies. The tunneling probability is then used to calculate the contact resistance as a function of doping for the contact. The contact resistances are approximately one‐half the resistances calculated using the WKB method.

ISSN:0002-9505    

DOI:10.1119/1.16861

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

The behavior of a gyroscope mounted in frictionless gimbal bearings when the outer ring is constrained to rotate at a constant rate is examined. The resulting motion of the rotor axis is described, accounted for by an elementary argument followed by a more complete treatment. The behavior of the rotor in an unusual parameter regime is also discussed. The equations of motion for a motor‐driven rotor are obtained and compared with the frictionless case.

ISSN:0002-9505    

DOI:10.1119/1.16862

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

It is shown that a conducting spheroid, which is moving uniformly along its axis of revolution, produces the same electromagnetic field as a moving line charge or a point charge or a charged disk, depending on the shape of the spheroid.

ISSN:0002-9505    

DOI:10.1119/1.16863

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

It is shown that a rigid rod, suspended horizontally by two springs, may be used to demonstrate all of the principal features of coupled harmonic oscillations. This simple system is easy to set up and analyze and has some interesting features not possessed by other coupled oscillation demonstrations. The coupling between translational motion of the center of mass (c.m.) and rotational motion about the c.m. can be easily adjusted by changing the springs and their points of attachment to the rod. The normal modes have simple interpretations as pure rotations about points away from the c.m. With proper choice of the parameters these points are located at the points of attachment of the springs. Surprisingly it is possible to measure normal mode frequencies without exciting pure normal mode motion.

ISSN:0002-9505    

DOI:10.1119/1.16864

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

Expansions of the volume integrals of strongly localized, continuous, differentiable electric charge and current densities are introduced in terms of the total charge, and variable and moving electric and magnetic dipoles, and conditions under which such expansions are applicable are determined. To enhance an understanding of the effects of external electromagnetic fields acting on very localized densities of electric charges and currents, the resulting Lorentz force, torque, and power are computed by using such expansions. To show how versatile variable and moving dipoles are for building physical models, the following are considered: (a) energy conversions by electric motors, by dielectric and induction heating, and by the magnetic drag force, and (b) relativistic effects in translational movements of steady electric and magnetic dipoles; in particular, the torque on a magnetic dipole moving parallel to a line carrying a steady current and uniformly distributed electric charges.

ISSN:0002-9505    

DOI:10.1119/1.16865

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

The time delay or the time advance in the scattering of simple one‐dimensional systems can be evaluated in a straightforward manner for certain potential models. It is found that when the interacting potential is attractive and has a strength such that it nearly supports an additional bound state, the time delay at small scattering energy is very large. On the other hand, if the potential supports a bound state with nearly zero binding energy, the time advance near threshold is anomalously large. The behavior of a wave packet scattering from the double delta‐function potential is also investigated.

ISSN:0002-9505    

DOI:10.1119/1.16866

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP

摘要:

A simple laboratory experiment is described for tracing light rays in a medium with spatially varying index of refraction. The analysis is at a level appropriate to an introductory optics course.

ISSN:0002-9505    

DOI:10.1119/1.16867

出版商:American Association of Physics Teachers    

年代:1992

数据来源: AIP