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Positive and negative birefringence of materials in microwave region
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| Pengarang | : | Sasa Ziherl; Mojca Cepic; Jurij Bajc |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 2) |
| Halaman | : | 110-118 |
| Abstrak | : | We present a set of experiments with microwaves that enable one to distinguish between isotropic and anisotropic properties of wooden materials. We also determine the magnitude and the sign of the birefringence of uniaxial materials. Due to the visible structure of wood and possible direct observation of the effects on the wave propagation, solid wood boards and particle boards can be used as persuasive representatives of positively and negatively birefringent materials, respectively. Suggested experiments can easily be used for demonstration purposes or laboratory work at the undergraduate or graduate level in optics courses. |
A toy model for the yield of a tamped fission bomb
| Pengarang | : | B. Cameron Reed |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 2) |
| Halaman | : | 105-109 |
| Abstrak | : | A simple expression is developed for estimating the yield of a tamped fission bomb, that is, a basic nuclear weapon comprising a fissile core jacketed by a surrounding neutron-reflecting tamper. This expression is based on modeling the nuclear chain reaction as a geometric progression in combination with a previously published expression for the threshold-criticality condition for such a core. The derivation is especially straightforward, as it requires no knowledge of diffusion theory and should be accessible to students of both physics and policy. The calculation can be set up as a single page spreadsheet. Application to the Little Boy and Fat Man bombs of World War II gives results in reasonable accord with published yield estimates for these weapons. |
Rosalind Franklins X-ray photo of DNA as an undergraduate optical diffraction experiment
| Pengarang | : | J. Thompson; G. Braun; D. Tierney; L. Wessels; H. Schmitzer; B. Rossa; H. P. Wagner; W. Dultz |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 2) |
| Halaman | : | 95-104 |
| Abstrak | : | Rosalind Franklin's X-ray diffraction patterns of DNA molecules rendered the important clue that DNA has the structure of a double helix. The most famous X-ray photograph, Photo 51, is still printed in most Biology textbooks. We suggest two optical experiments for undergraduates that make this historic achievement comprehensible for students by using macromodels of DNA and visible light to recreate a diffraction pattern similar to Photo 51. In these macromodels, we replace the double helix both mathematically and experimentally with its two-dimensional (flat) projection and explain why this is permissible. Basic optical concepts are used to infer certain well-known characteristics of DNA from the diffraction pattern. |
Mechanics and statistics of the worm-like chain
| Pengarang | : | Joseph P. Ndenda |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 2) |
| Halaman | : | 86-94 |
| Abstrak | : | The worm-like chain model is a simple continuum model for the statistical mechanics of a flexible polymer subject to an external force. We offer a tutorial introduction to it using three approaches. First, we use a mesoscopic view, treating a long polymer (in two dimensions) as though it were made of many groups of correlated links or “clinks,” allowing us to calculate its average extension as a function of the external force via scaling arguments. We then provide a standard statistical mechanics approach, obtaining the average extension by two different means: the equipartition theorem and the partition function. Finally, we work in a probabilistic framework, taking advantage of the Gaussian properties of the chain in the large-force limit to improve upon the previous calculations of the average extension. |
Coefficient of rolling friction - Lab experiment
| Pengarang | : | Leonid Minkin; Daniel Sikes |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 77-78 |
| Abstrak | : | With rare exception,1–3 the force of friction on a rolling object is not usually a topic discussed in introductory physics textbooks. Although the invention of the wheel is one of the essential world achievements, rolling friction is typically ignored and the inability of students to explain or model the deceleration of a rolling rigid object on a rigid horizontal surface necessitates a mechanism for this phenomenon. (Detailed analyses of this mechanism and measurements of the coefficient of rolling friction can be found in Refs. 4–6.) Every introductory physics textbook discusses kinetic and static friction and many papers are devoted to teaching these forces,7 but it is well known that measuring static and kinetic friction in educational labs is troublesome. |
Race to improve student understanding of uncertainty: Using LEGO race cars in the physics lab
| Pengarang | : | Maria Parappilly; Christopher Hassam; Richard J. Woodman |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 68-76 |
| Abstrak | : | Laboratories using LEGO race cars were developed for students in an introductory physics topic with a high early drop-out rate. In a 2014 pilot study, the labs were offered to improve students' confidence with experiments and laboratory skills, especially uncertainty propagation. This intervention was extended into the intro level physics topic the next year, for comparison and evaluation. Considering the pilot study, we subsequently adapted the delivery of the LEGO labs for a large Engineering Mechanics cohort. A qualitative survey of the students was taken to gain insight into their perception of the incorporation of LEGO race cars into physics labs. For Engineering, the findings show that LEGO physics was instrumental in teaching students the measurement and uncertainty, improving their lab reporting skills, and was a key factor in reducing the early attrition rate. This paper briefly recalls the results of the pilot study, and how variations in the delivery yielded better learning outcomes. A novel method is proposed for how LEGO race cars in a physics lab can help students increase their understanding of uncertainty and motivate them towards physics practicals. |
Parallel programming with Easy Java Simulations
| Pengarang | : | F. Esquembre; W. Christian; M. Belloni |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 54-67 |
| Abstrak | : | Nearly all of today's processors are multicore, and ideally programming and algorithm development utilizing the entire processor should be introduced early in the computational physics curriculum. Parallel programming is often not introduced because it requires a new programming environment and uses constructs that are unfamiliar to many teachers. We describe how we decrease the barrier to parallel programming by using a java-based programming environment to treat problems in the usual undergraduate curriculum. We use the easy java simulations programming and authoring tool to create the program's graphical user interface together with objects based on those developed by Kaminsky [Building Parallel Programs (Course Technology, Boston, 2010)] to handle common parallel programming tasks. Shared-memory parallel implementations of physics problems, such as time evolution of the Schrödinger equation, are available as source code and as ready-to-run programs from the AAPT-ComPADRE digital library. |
Recommendations for the use of notebooks in upper-division physics lab courses
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 45-53 |
| Abstrak | : | The use of lab notebooks for scientific documentation is a ubiquitous part of physics research. However, it is common for undergraduate physics laboratory courses not to emphasize the development of documentation skills, despite the fact that such courses are some of the earliest opportunities for students to start engaging in this practice. One potential impediment to the inclusion of explicit documentation training is that it may be unclear to instructors which features of authentic documentation practice are efficacious to teach and how to incorporate these features into the lab class environment. In this work, we outline some of the salient features of authentic documentation, informed by interviews with physics researchers, and provide recommendations for how these can be incorporated into the lab curriculum. We do not focus on structural details or templates for notebooks. Instead, we address holistic considerations for the purpose of scientific documentation that can guide students to develop their own documentation style. While taking into consideration all the aspects that can help improve students' documentation, it is also important to consider the design of the lab activities themselves. Students should have experience with implementing these authentic features of documentation during lab activities in order for them to find practice with documentation beneficial. |
Geometrical optics of doves
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 157 |
| Abstrak | : | Here, we see doves strolling and drinking in a shallow body of water. They cast a shadow on the bottom and are reflected by the surface of the water. The positions of the two images (shadow and specular reflection) follow different geometries. In particular, the position of the mirror image does depend on the position of the observer, while that of the shadow does not. |
The electric field of a uniformly charged cubic shell
| Pengarang | : | Kaitlin McCreery; Henry Greenside |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 36-44 |
| Abstrak | : | As an integrative and insightful example for undergraduates learning about electrostatics, we discuss how to use symmetry, Coulomb's law, superposition, Gauss's law, and visualization to understand the electric field ?(?,?,?) produced by a uniformly charged cubic shell. We first discuss how to deduce qualitatively, using freshman-level physics, the perhaps surprising fact that the interior electric field is nonzero and has a complex structure, pointing inwards from the middle of each face of the shell and pointing outwards towards each edge and corner. We then discuss how to understand the quantitative features of the electric field by plotting an analytical expression for E along symmetry lines and on symmetry surfaces of the shell. |