ISSN:0002-9505    

DOI:10.1119/1.15083

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.15086

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.15090

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.15069

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

This Resource Letter provides a guide to the literature on musical acoustics. The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field. The letter I, for intermediate level, indicates material of a somewhat more specialized nature; and the letter A indicates rather specialized or advanced material. An asterisk (*) indicates articles that are especially useful or interesting; a double asterisk (**) indicates those articles to be included in an accompanying Reprint Book.

ISSN:0002-9505    

DOI:10.1119/1.15070

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

What is the thermal efficiency of a heat engine producing the maximum possible work per cycle consistent with its operating‐temperature range? This question is answered here for four model reversible heat engine cycles. In each case, the work is maximized with respect to two characteristic temperatures that are intermediate between the maximum and minimum cycle temperaturesT+andT−. The maximum‐work efficiencies are found to equal or be well approximated by η*=1−(T−/T+)1/2. Because this efficiency is a function solely of the extreme cycle temperatures, it can be compared easily with the corresponding reversible Carnot cycle efficiency ηc=1−T−/T+. Here, η*, which is a much better guide to the performance of actual heat engines than ηc, is the same efficiency found by Curzon and Ahlborn [Am. J. Phys.43, 22 (1975)] for a model irreversible heat engine operating at maximumpoweroutput. The present results show that η* is more ‘‘universal’’ than had been realized previously. If the work output per cycle is keptfixed, the thermal efficiency η of each cycle considered here can be increased by enlarging the heat engine and operating it at less‐than‐maximum work output per cycle. Formally, for such afixedwork output, η can approach the Carnot efficiency ηcin the limit of infinite engine size.

ISSN:0002-9505    

DOI:10.1119/1.15071

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The resonant frequencies of a sinusoidally driven system are usually defined as those for which some physical response is a relative maximum. There is also a tendency to define them as frequencies for which the reactance of the system vanishes, since zero‐reactance frequencies are often approximately equal to maximum‐response frequencies and are sometimes easier to calculate. However, there are many systems for which the two types of frequencies are significantly different. There are also systems for which the reactance does not vanish in certain frequency ranges, though maximum responses still occur. It is concluded that vanishing reactance is not valid as a general criterion for resonance, and students should be warned against its use.

ISSN:0002-9505    

DOI:10.1119/1.15072

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The mechanism by which a traveling transverse wave in a string stores momentum and transports energy is studied. The existence of longitudinal waves with much higher propagation speed is shown to be essential.

ISSN:0002-9505    

DOI:10.1119/1.15073

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

Our teaching of electromagnetism at the noncalculus level, whether in high school or college, should be based upon Maxwell’s equations, just as we customarily base our discussions of mechanics upon Newton’s second law of motion. Both the second law and Maxwell’s equations are differential equations; but each has an algebraic representation which is fruitful in many applications. An algebraic formulation of Maxwell’s equations is presented, along with some suggestions for teaching Maxwell’s equationsabinitiobased upon experiences accrued at Newton South since the 83/84 academic year.

ISSN:0002-9505    

DOI:10.1119/1.15074

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The motion of a simple pendulum in nearly elliptical orbits is studied to determine the direction of precession due to various effects. With a pendulum of small angle, an extra magnetic attraction toward the center of force causes forward precession, whereas a magnetic repulsion causes retrograde motion; both these effects are described by a simple mathematical model. A pendulum with a larger angle of swing undergoes marked forward precession and this effect can be calculated to second order in the angle of swing. By contrast, a two‐dimensional motion with an extra perturbation designed to simulate the effects of a large angle of swing yields a small retrograde effect.

ISSN:0002-9505    

DOI:10.1119/1.15075

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP