ISSN:0002-9505    

DOI:10.1119/1.18344

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18392

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18447

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18327

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.18328

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

One class of explanations of the null result of the Trouton–Noble experiment uses the ‘‘standard’’ definitions of electromagnetic energy and momentum but is quite complicated. Another class is much simpler but appears to require new definitions of electromagnetic energy and momentum. We reconcile the two sets of explanations and show that they are both physically correct. We use the same arguments that have been used in discussions of the famous ‘‘4/3’’ factor in the electromagnetic mass of the classical electron.

ISSN:0002-9505    

DOI:10.1119/1.18329

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

In a previous paper we described details of the construction of stabilized 670‐nm diode lasers for use in undergraduate physics laboratories. We report here a series of experiments that can be performed using the 670‐nm diode laser, a homemade scanning Fabry–Perot cavity, a helium–neon laser, a simple photodiode, and a few pieces of electronics hardware. The experiments include: (1) an introduction to the scanning confocal Fabry–Perot cavity, and to its use as an optical spectrum analyzer; (2) laser frequency modulation and observation of FM sidebands using the optical spectrum analyzer; and (3) the Pound–Drever method for servo‐locking a Fabry–Perot cavity to a laser. These experiments are relatively easy to set up and perform, yet they demonstrate a number of useful optical principles and experimental techniques.

ISSN:0002-9505    

DOI:10.1119/1.18330

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

Laser spectroscopy of the cesium dimer is presented for use in an undergraduate laboratory. The experimental apparatus consists of near 780‐nm diode lasers, a glass cesium cell, a simple oven, and a monochromator. The experiment can be assembled quickly and at low cost. In the course of this experiment students can observe vibrational structure in molecular emission and learn about potential energy curves and Franck–Condon factors. The first vibrational constant of theX1Σg+ground state is measured to be 42.7±1.6 cm−1.

ISSN:0002-9505    

DOI:10.1119/1.18331

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

A stationary dew drop assumes a shape that minimizes the sum of its gravitational and surface energies. This shape, however, cannot be described by a mathematical function in closed form because the governing differential equations of the drop do not admit of an analytical solution but must be integrated numerically to yield the drop profile. Hence, this problem provides a good case for using the calculus of variations to obtain the governing differential equations and presents advanced students with an opportunity to gain insight and experience in numerical computations involving a real and interesting physical problem. In this paper we obtain the differential equations governing the shape of the drop in two ways: (i) by considering the balance of forces on the drop in static equilibrium; (ii) by seeking the profile which minimizes the total energy of the drop through the use of the calculus of variations. The resulting differential equations are then integrated numerically to obtain the theoretical profile. Two computational strategies, one for each of the two classes of wetting and nonwetting drops, are discussed. Further, it is shown how one may obtain the values of the surface tension and the contact angle for a liquid drop by matching the computed profile to the experimentally observed shape.

ISSN:0002-9505    

DOI:10.1119/1.18332

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP

摘要:

The well‐known discussion on an engine consisting of a ratchet and a pawl in [R. P. Feynman, R. B. Leighton, and M. Sands,TheFeynmanLecturesonPhysics(Addison‐Wesley, Reading, MA, 1963), Vol. 1, pp. 46.1–46.9] is shown to contain some misguided aspects: Since the engine issimultaneouslyin contact with reservoirs at different temperatures, it can never work in a reversible way. As a consequence, the engine can never achieve the efficiency of a Carnot cycle, not even in the limit of zero power (infinitely slow motion), in contradiction with the conclusion reached in theLectures.

ISSN:0002-9505    

DOI:10.1119/1.18393

出版商:American Association of Physics Teachers    

年代:1996

数据来源: AIP