美国物理学杂志 (AJP) 的使命是发表有关物理学教育和文化方面的文章，这些文章对物理学学生、教育工作者和研究人员的不同受众来说是有用的、有趣的和可访问的。我们的读者通常会在他们的专业之外阅读，以扩大他们对物理学的理解，并在本科和研究生阶段扩展和增强他们的教学工具包。

The mission of the American Journal of Physics (AJP) is to publish articles related to physics education and culture that are useful, interesting, and accessible to a diverse audience of physics students, educators, and researchers. Our readers often read beyond their professional fields to broaden their understanding of physics and to expand and enhance their teaching toolkit at the undergraduate and graduate levels.

《American Journal of Physics》（美国物理学杂志，AJP）的使命是发表与物理学教育和文化相关的文章，这些文章对物理学学生、教育工作者和研究人员等不同受众具有实用性、趣味性和可读性。我们的读者通常会在专业领域之外进行阅读，以拓宽他们对物理学的理解，并在本科和研究生阶段扩展和丰富他们的教学工具。

American Journal of Physics

An investigation of students’ knowledge after a traditional advanced high-school course in electromagnetism shows deficiencies of their knowledge in three major areas: (1) the structure of knowledge—e.g., realizing the importance of central ideas, such as Maxwell’s equations (expressed qualitatively); (2) conceptual understanding—e.g., understanding the relationships between the electric field and its sources; and (3) application of central relationships in problem solving. To remedy these deficiencies we propose an instructional model which integrates problem solving, conceptual understanding and the construction of the knowledge structure. The central activity of the students is a gradual construction of a hierarchical concept map organized around Maxwell’s equations as central ideas of the domain. The students construct the map in five stages: (1) SOLVE—they solve a set of problems that highlight the central ideas in the domain; (2) REFLECT—they reflect on the conceptual basis of their solutions; (3) CONCEPTUALIZE—they perform activities that deal with relevant conceptual difficulties; (4) APPLY—they carry out complex applications; (5) LINK—they link their activities to the evolving concept map. This integrative model (experimental treatment) was compared to an isolated treatment of drill and practice or treatment of conceptual difficulties without linkage to the proposed knowledge structure. The comparison shows that students in the experimental treatment performed better than the other students on measures of recall, conceptual knowledge and problem solving. Students in the experimental treatment were also able to transfer and extract central ideas in a domain different than physics.

Esther Bagno

Bat-Sheva Eylon

From problem solving to a knowledge structure: An example from the domain of electromagnetism

The effect of an external magnetic field B on magnetic materials is a subject of immense importance. The simplest and oldest manifestation of such effects is the behavior of the magnetic compass. Magnetization M plays a key role in studying the response of magnetic materials to B. In this paper, an experimental technique for the determination of M of a permanent magnet will be presented. The proposed method discusses the effect of B (produced by a pair of Helmholtz coils) on a permanent magnet, suspended by two strings and allowed to oscillate under the influence of the torque that the magnetic field exerts on the magnet. The arrangement used Newton's second law for rotational motion to measure M via graphical analysis.

B. Barman

A. Petrou

Measuring the magnetization of a permanent magnet

测量永磁体的磁化强度

Contact angle is an important parameter in characterizing the wetting properties of fluids. For this reason, accurate measurement of the contact angle at liquid-solid interfaces is of great importance in industrial and scientific applications. The most common method for measuring the contact angle is to obtain it directly from the profile of a sessile drop. Though convenient, this method suffers from certain inherent drawbacks. Here, we describe an alternative method that uses the height and volume of a sessile drop as constraints to construct its profile by numerical integration of two parametric differential equations. The integration yields, self consistently, the average value of the contact angle along the entire contact line as well as the footprint radius of the drop and its crown radius of curvature. As a test case, the new method is used to obtain the contact angle of pure water on two different substrates, Teflon and Lucite. For each substrate, four drops ranging in volume from 10. to 40 μl are used. The computed contact angles are consistent across the four different drop sizes for each substrate and are in good agreement with the literature values.

F. Behroozi

P. S. Behroozi

Reliable determination of contact angle from the height and volume of sessile drops

This paper theoretically studies a simple system of two identical linear springs connected symmetrically to a mass in a V-shaped configuration, with an additional adjustable external force applied to the mass. As this force is varied, under certain conditions the equilibrium position of the mass demonstrates strong dependence on the history of changes in the external force, exhibiting hysteresis. Mathematically, variations of the external force cause the system to undergo two saddle-node bifurcations at two differing critical points, leading separately to the creation and destruction of branches of stable equilibria. Analysis of the bifurcation diagram shows that the saddle-node bifurcations cause hysteresis in the system, and the behavior is summarized in a hysteresis graph.

Christopher Ong

Hysteresis in a simple V-shaped spring-mass system

简单V形弹簧-质量系统中的滞后现象

The efficiency of a Carnot engine is treated for the case where the power output is limited by the rates of heat transfer to and from the working substance. It is shown that the efficiency, η, at maximum power output is given by the expression η = 1 − (T2/T1)1/2 where T1 and T2 are the respective temperatures of the heat source and heat sink. It is also shown that the efficiency of existing engines is well described by the above result.

F. L. Curzon

B. Ahlborn

Efficiency of a Carnot engine at maximum power output

卡诺发动机在最大功率输出时的效率

There are a few exactly solvable potentials in quantum mechanics for which the completeness relation of the energy eigenstates can be explicitly verified. In this article, we give an elementary proof that the set of bound (discrete) states together with the scattering (continuum) states of the reflectionless potential form a complete set. We also review a direct and elegant derivation of the energy eigenstates with proper normalization by introducing an analog of the creation and annihilation operators of the harmonic oscillator problem. We further show that, in the case of a single bound state, the corresponding wave function can be found from the knowledge of continuum eigenstates of the system. Finally, completeness is shown by using the even/odd parity eigenstates of the Hamiltonian, which provides another explicit demonstration of a fundamental property of quantum mechanical Hamiltonians.

Fatih Erman

O. Teoman Turgut

Completeness of energy eigenfunctions for the reflectionless potential in quantum mechanics

量子力学中无反射势的能量本征函数的完备性

Editor's Note: A straightforward approximate algebraic procedure for introducing locally flat coordinates in a Schwarzschild spacetime is undertaken in this Comment on the recent leading order differential approach elucidated by Steven Balbus in the June 2024 issue. It is very likely that instructors even in special relativity could employ this technique and thereby obtain the correct deflection angle for light in an accelerated frame of reference.

Frank Wang

Comment on “Determining the difference between local acceleration and local gravity: Applications of the equivalence principle to relativistic trajectories” [Am. J. Phys. <b>92</b>(6), 444–449 (2024)]

对“确定局部加速度与局部重力之间的差异：等效原理在相对论轨迹中的应用”[美国物理学期刊<b>92</b>(6), 444–449 (2024)]的评论

We discuss the regions forbidden to classical scattering trajectories by repulsive potentials. We give explicit results for the asymptotic form of these regions, far from the scattering center, in terms of the scattering angle function. We account for divergent total cross sections on the basis of these results.

Thomas Curtright

Gaurav Verma

Scattering shadows

散射阴影

The Poisson spot is a fascinating lecture demonstration. Its simple explanation can lead to further questions, not only the one posed in the title, but also questions such as why the simple model that considers only light passing just outside the spherical object is successful. The Huygens–Fresnel diffraction model is applied to answer these questions.

Jami J. Kinnunen

Why is there no Poisson spot in a solar eclipse?

为什么日食中没有泊松光斑？

“I can't help but see physics everywhere I go now.” This quotation from students' evaluations summarizes what I consider to be the most important learning outcome. I will discuss our efforts to make introductory physics a meaningful and enjoyable journey rather than a survival experience in weed-out classes. There is no single recipe to achieve that, but I'll share some ideas and resources that we have created. Additionally, I will discuss several new outreach programs that we introduced with the help of our students. Outreach is not just a service that we provide for the benefit of the public; it is an integral part of the learning experience for the students.

Tatiana Erukhimova

2024 David Halliday and Robert Resnick Award for Excellence in Undergraduate Physics Teaching Lecture: It's not business, it's personal. Teaching large classes, one student at a time

Abbreviation	Am. J. Phys.
Journal Impact	0.64
Quartiles(Global)	PHYSICS, MULTIDISCIPLINARY(Q3)

ISSN	0002-9505, 1943-2909
h-index	110

Publication Information	Publisher: American Association of Physics Teachers，Publishing cycle: Monthly，Journal Type: journal，Open Access Journals: No
Basic data	Year of publication: 1996，Proportion of original research papers: 99.10%，Self Citation Rate:25.00%， Gold OA Rate: 11.02%
Average review cycle	网友分享经验：平均3.0个月
Average recruitment ratio	网友分享经验：容易

American Journal of Physics

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