摘要:

There are many examples of interesting optical phenomena involving virtual images arising from refraction at the interface(s) between air and some transparent solid or liquid. However, because it is cumbersome to interpret analytical expressions or to sketch diagrams using Snell’s law of refraction, students rarely explore and develop a qualitative understanding of these phenomena. In this paper we introduce a simple‐to‐use linear approximation for single‐surface refraction and show how it leads to qualitatively correct descriptions of some interesting but complex optical phenomena. In particular, we analyze the virtual images formed when looking at objects through both rectangular blocks and triangular prisms. The refraction images observed through a triangular prism are particularly interesting pedagogically and also provide a physical means to distinguish between objects located just outside and just inside, or on, the prism’s surface.

ISSN:0002-9505    

DOI:10.1119/1.18213

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The resonant tunneling of a wave packet is studied, for a one‐dimensional double barrier, by solving the time‐dependent Schrödinger equation. The transmission is determined as a function of the spatial width of the incident wave packet. It is shown that if the double barrier acts as an energy filter, then the spatial width of the transmitted wave packet is increased, due to the trapping of the particle between the two barriers for a time, ℏ/Γ, where Γ is the width of the resonance. The reflected wave packet consists of two components: one corresponding to reflection from the first barrier and the other due to the particle being trapped between the barriers for a time ℏ/Γ.

ISSN:0002-9505    

DOI:10.1119/1.18214

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

We examine the motion of soft drink cans rolling down an incline as a function of the amount of water in the can. Our observations show this behavior to be remarkably complex. We introduce models suggested by the experimental results which describe the limiting cases of a nonviscous fluid and an infinitely viscous fluid, and compare the results of the model calculations to our observations.

ISSN:0002-9505    

DOI:10.1119/1.18215

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

We present a simple and inexpensive calorimetric system that has been implemented in the undergraduate students laboratory of thermodynamics at the Physics Faculty of the University of Barcelona. It is shown that, after proper calibration, the system enables measurement of the relevant thermodynamic quantities at a first‐order phase transition. As an example, the solid–liquid phase transition of water can be studied: Students find that both the change in specific heat and the latent heat (and its temperature dependence) coincide within the experimental scatter with the values given in the literature.

ISSN:0002-9505    

DOI:10.1119/1.18216

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Linear, one‐dimensional, analytical, and numerical models for seiches (standing waves) existing at the surface and on the internal interface between the upper warm and bottom cold layers for a long, narrow lake are developed. Using the specific bathymetric and thermal structures of a lake, Lake Champlain, these models predict the periods, nodal locations, vertical displacements, and current velocities associated with the fundamental and higher‐order modes. Modeled results are compared with historical limnological data obtained from Lake Champlain. Agreement is good for the periods of the first few modes of the surface and internal seiches; however, predicted current velocities associated with the internal seiche are about half as large as those actually observed.

ISSN:0002-9505    

DOI:10.1119/1.18217

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

This paper deals with the problem of obtaining the electric field near a region of magnetic flux, whose geometry has cylindrical symmetry. We derive an expression for a direct calculation of the induced electric field vector in geometric situations where a slowly varying magnetic field is confined to a long solenoid of arbitrary cross section. We check our result in a standard case, then we use it in a nontrivial case to confirm its utility. The developed expression can also be used to provide numerical evaluation of the field within the class of cylindrical symmetry.

ISSN:0002-9505    

DOI:10.1119/1.18218

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A simple method based on the enumeration of all random walk configurations for a very reduced number of steps is used to obtain the critical exponent ν for self‐avoiding random walks in two and three dimensions.

ISSN:0002-9505    

DOI:10.1119/1.18219

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The motion of ions above the earth’s atmosphere is introduced by discussing the nonrelativistic motion of a charged particle in the field of a stationary magnetic dipole. Unlike the Kepler or Coulomb problem, no way is known to separate our problem into one‐dimensional problems andafortiorian exact analytic solution is not known. However, an effective potential can be identified whose study clarifies the qualitative and semiquantitative features of the bound states. We ask about the periodicity of bound states, taken for granted by one exposed only to the Kepler or Coulomb problem, and show how consideration of phase space can provide a partial answer, Poincaré recurrence. The treatment is accessible to students who have a first acquaintance with the canonical formalism and Liouville’s theorem, for example first‐year graduate students.

ISSN:0002-9505    

DOI:10.1119/1.18220

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The use of inexpensive pressure sensors, with minimum installation problems, has allowed several experiments to be designed for the physics class. An experimental device provided with a pressure sensor and a level sensor has now made it possible to verify the fundamental equation of fluid statics. The device has been applied to density measurements of several fluids (water, aqueous solution of NaCl and ethanol) at constant temperature.

ISSN:0002-9505    

DOI:10.1119/1.18221

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

As a continuation of part I of this work, further experiments were designed for the physics class using pressure sensors. An experimental setup using a pressure sensor and two optical fiber sensors makes it possible to verify the Hagen–Poiseuille equation, to measure the viscosity of several gases and, by analogy with an electric current circuit, to verify that the parallel and series association of flow resistance may be solved as if they were electrical resistances.

ISSN:0002-9505    

DOI:10.1119/1.18222

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP