OPAC - Pencarian Artikel Jurnal & Majalah Library USD
Menampilkan semua artikel (Halaman 669 dari 34170, Total: 341698 data)
Snow spheres and ice cubes
klik untuk membaca file PDF
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 156 |
| Abstrak | : | In standard calculus textbooks—usually as a problem on related rates—it is shown that for a snowball melting at a rate proportional to its surface area, its radius decreases at a constant rate regardless of its initial size. A further assumption (usually unstated) is that the snowball remains spherical as it melts. |
Changes in AP Physics courses effective 2024–2025
| Pengarang | : | James Lincoln |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 154-155 |
| Abstrak | : | Taking effect in fall 2024, and showing up on the May 2025 exam, all of the AP Physics courses will be going through some changes. The biggest change is that AP Physics 1 will be gaining a unit on Fluid Physics, transplanted from AP Physics 2 (Fig. 1).1 On the other hand, AP Physics C: Mechanics and AP Physics C: Electricity and Magnetism will be receiving exam length increases and free-response question standardization. In this article, I provide some details of these changes and others, as described by the College Board.1 Because there are so many more of us teaching AP Physics 1, I also provide some extra details about the “new” unit on fluids. In the fall of 2024, when the changes are finalized with additional details, I will provide an update to this article. |
Two famous results of Einstein derived from the Jarzynski equality
| Pengarang | : | Fred Gittes |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 31-35 |
| Abstrak | : | The Jarzynski equality (JE) is a remarkable statement relating transient irreversible processes to infinite-time free energy differences. Although 20 years old, the JE remains unfamiliar to many; nevertheless, it is a robust and powerful law. We examine two of Einstein's most simple and well-known discoveries, one classical and one quantum, and show how each of these follows from the JE. Our first example is Einstein's relation between the drag and diffusion coefficients of a particle in Brownian motion. In this context, we encounter a paradox in the macroscopic limit of the JE which is fascinating but also warns us against using the JE too freely outside of the microscopic domain. Our second example is the equality of Einstein's B coefficients for absorption and stimulated emission of quanta. Here, resonant light does irreversible work on a sample, and the argument differs from Einstein's equilibrium reasoning using the Planck black-body spectrum. We round out our examples with a brief derivation and discussion of Jarzynski's remarkable equality. |
Physics of holiday lights
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 152 |
| Abstrak | : | While “goofing” around with my 365-nm LED flashlight, I happened to accidentally light upon my Christmas tree LED light strand. The incident UV light caused the core of the bulb to glow a bright whitish color, as seen in Fig. 1. Why should that be? It turns out that many “white” LEDs are produced by using a blue LED bulb coated with a yellow phosphor, which produces white light by phosphorescence.1 |
Demonstrating the conservation of angular momentum using spherical magnets
| Pengarang | : | Johan Linden; Joakim Slotte; Kjell-Mikael Källman |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 25-30 |
| Abstrak | : | An experimental setup for demonstrating the conservation of angular momentum of rotating spherical magnets is described. Two spherical Nd-Fe-B magnets are placed on a double inclined plane and projected towards each other with pre-selected impact parameters ranging from zero to a few tens of millimeters. After impact, the two magnets either revolve vigorously around the common center of mass or stop immediately, depending on the value of the impact parameter. Using a pick-up coil connected to an oscilloscope, the angular frequency for the rotating magnets was measured, and an estimate for the angular momentum was obtained. A high-speed video camera captured the impact and was used for measuring linear and angular velocities of the magnets. A very good agreement between the initial angular momentum before the impact and the final angular momentum of the revolving dumbbell is observed. The two rotating magnets, and the rotating electromagnetic field emanating from them, can also be viewed as a toy model for the newly discovered gravitational waves, where two black holes collide after revolving around each other. |
The circular Atwood machine
| Pengarang | : | Arturo Carlos Marti |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 150-151 |
| Abstrak | : | The Atwood machine, a traditional device in physics, has been an invaluable tool for demonstrating and understanding the fundamental principles of Newtonian mechanics, especially Newton’s second law.1 Some time ago, we published in this column a proposal that makes use of the smartphones and their built-in sensors to implement an updated version of the experiment but keeping its essence unchanged.2 Now, we propose a circular Atwood machine designed to study the relationship between the external torque on a rigid disk and its angular acceleration mediated through the moment of inertia. In our proposal, quantitative measuments are achieved by means of a smartphone’s angular velocity sensor. The moment of inertia measured was successfully contrasted with the value obtained from the period of oscillations of the device hanging from a point at its periphery. |
Harmonic oscillator thermal density matrix: First-order differential equations for the position representation
| Pengarang | : | L. F. Barragán-Gil; R. Walser |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 22-24 |
| Abstrak | : | A first-order partial differential equation is derived whose solution enables us to find straightforwardly the off-diagonal matrix elements in the position representation of the harmonic oscillator density operator. This approach constitutes an alternative to techniques that require advanced knowledge of mathematical and quantum mechanical results. |
Physics bachelors’ outcomes
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 149 |
| Abstrak | : | In the Statistical Research Center, we have been collecting data from recent physics degree recipients for decades. Typically, about half of physics bachelor’s degree recipients pursue graduate study. This held true for the classes of 2019 and 2020, with ∼48% matriculating into graduate programs and ∼46% obtaining employment. The remaining 6% reported being unemployed (and pursuing employment) within 12 months of their graduation. Students graduating in 2019 and 2020 were faced with the impacts of the COVID-19 pandemic, so the unemployment rate was a bit higher than it typically is. |
Revisiting the round bottom flask rainbow experiment
| Pengarang | : | Markus Selmke; Sarah Selmke |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 86 (No. 1) |
| Halaman | : | 14-21 |
| Abstrak | : | A popular demonstration experiment in optics uses a round-bottom flask filled with water to project a circular rainbow on a screen with a hole through which the flask is illuminated. We show how the vessel's wall shifts the first- and second-order bows towards each other and consequently reduces the width of Alexander's dark band. We address the challenge this introduces in observing Alexander's dark band, and explain the importance of a sufficient distance between the flask and the screen. The wall-effect also introduces a splitting of the bows that can easily be misinterpreted. |
The Physical Application of a Triangle Approximation Model
| Pengarang | : | Hongbo Fu |
| Nama Majalah/Jurnal | : | The Physics Teacher |
| Volume / Edisi | : | 62 (No. 2) |
| Halaman | : | 145-147 |
| Abstrak | : | In this paper, three approximation laws related to a triangle are proposed, and a specific model is developed. First, when the apex angle of an isosceles triangle tends to zero, the bottom two angles of the triangle are each approximately 90°. Second, the two sides of this triangle are approximately perpendicular to the base. Third, the length of the base in the triangle is approximately the same as the arc length. This model can help teachers explain abstract mathematical limit processes in physical problems through the intuitiveness of geometric figures. We have applied this model to a series of typical physics examples, including centripetal acceleration in uniform circular motion, Ampere’s law, Young’s double-slit interference, and the electric potential of the electric dipole, to prove its validity and practicality. |