ISSN:0002-9505    

DOI:10.1119/1.17730

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17731

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Thermodynamics in introductory physics typically begins with the ideas of temperature and heating and with the first law of thermodynamics. Then the more difficult parts come: entropy and the second law of thermodynamics. This second portion of the course can begin with a microscopic conception of entropy and a qualitative idea of how thermal systems evolve. The key concept is the ‘‘multiplicity of a macrostate:’’ the number of microstates associated with a macrostate. Starting from these notions—a point of departure and a concept—this paper develops the second law of thermodynamics, the relationship ΔS≥(energy input by heating)/T, and the Carnot efficiency. Offer the entire development both as a specific alternative to what appears in typical introductory texts and as a contribution to a continuing discussion of how to teach thermodynamics to various college audiences.

ISSN:0002-9505    

DOI:10.1119/1.17732

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

The famous ‘‘1917 paper’’ of Einstein on the Quantum Theory of Radiation is revisited. Emphasis is placed on the little‐known bulk of the paper dealing with momentum balance. The most difficult part of the calculation is here simplified by regarding the ‘‘drag force’’ on a body moving within a blackbody cavity as due to the same quantized impulses that give rise to random recoil.

ISSN:0002-9505    

DOI:10.1119/1.17737

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Many static configurations involving electrical currents and charges possess angular momentum in electromagnetic form; two examples are discussed here, an electric charge in the field of a magnetic dipole, and an electric charge in the vicinity of a long solenoid. These provide clear evidence of the physical significance of the circulating energy flux indicated by the Poynting vector, as the angular momentum of the circulating electromagnetic energy can be converted to mechanical angular momentum by turning off the magnetic field. Electromagnetic momentum is created whenever electric fields change in the presence of a magnetic field and whenever magnetic fields change in the presence of an electric field. When simple dielectrics are involved, the momentum density can be resolved into two components, a pure‐field component ε0E×Band a component χeε0E×Bassociated with the polarization of the dielectric, the sum being εrε0E×B=D×B. It is argued that the latter component should be considered to be part of the electromagnetic momentum density, whose value then isD×B.

ISSN:0002-9505    

DOI:10.1119/1.17738

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

A demonstration apparatus is described suitable for use in a large lecture hall, in which the ‘‘pinch effect’’ applied to an empty aluminum soft drink can provides a dramatic and instructive example of induction and of the repulsion of oppositely directed current elements. The can is placed in a coil into which a short pulse of electrical current is driven from a charged capacitor. The current in the primary coil induces an oppositely directed current in the can wall, and the portion of the can under the coil is driven violently inward, pinching the can down to form a waist, or with a larger charge on the storage capacitor, separating it into two pieces.

ISSN:0002-9505    

DOI:10.1119/1.17739

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

A problem on the Atwood’s machine is often introduced early in the teaching of dynamics to demonstrate the application of Newton’s laws to the motion of a compound system. In a series of preliminary studies, student understanding of the Atwood’s machine was examined after this topic had been covered in a typical calculus‐based course. Analysis of the data revealed that many students had serious difficulties with the acceleration, the internal and external forces, and the role of the string. The present study was undertaken to obtain more detailed information about the nature and prevalence of these difficulties and thus provide a sound basis for the design of more effective instruction. The context for the investigation is a group of related problems involving less complicated compound systems. Specific examples illustrate how this research, which was conducted primarily in a classroom setting, has served as a guide in the development of tutorial materials to supplement the lectures and textbook in a standard introductory course.

ISSN:0002-9505    

DOI:10.1119/1.17740

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

A mechanical rotating oscillator is used to demonstrate different bent tuning curves with basically the same system. A softening restoring force is realized by operating the oscillator as a gravitational pendulum. A hardening restoring force is realized by a spring acting on the oscillator. Tuning curves which are bent either to the right or to the left, as well as bistability and the jump effect, can be demonstrated. Furthermore, a doubly bent curve of amplitude versus frequency is shown to exist which gives rise to a doubly bent tuning curve and tristability. The experiments are a good introduction to unexpected phenomena related to nonlinear physics.

ISSN:0002-9505    

DOI:10.1119/1.17741

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Analysis of the dynamics of an amusement‐park ride reveals that the passengers experience chaotic motion.

ISSN:0002-9505    

DOI:10.1119/1.17742

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP

摘要:

Simple apparatus, suitable for an undergraduate laboratory, allows precise measurements of the forward characteristics of Si and Ge ‘‘transdiodes’’ at different temperatures in the range 150–300 K. The experimental results are used to obtain a fairly accurate value of the universal constante/k(elementary charge to Boltzmann constant ratio) and of the energy gap of Si and Ge.

ISSN:0002-9505    

DOI:10.1119/1.17713

出版商:American Association of Physics Teachers    

年代:1994

数据来源: AIP