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Theoretical teaching of the work done by inertia  forces and its practical applications  CHEN Chi-yi College Physics    2024, 43 (11): 26-.   DOI: 10.16854/j.cnki.1000-0712.240156 Abstract （1160）      PDF（pc） （548KB）（398）       Knowledge map    Save This article addresses the calculation of the work done by inertia forces in the teaching of theoretical mechanics. It introduces an equivalent description of inertial forces based on the physics of reference frames. Based on this, the work done by inertia forces is re-examined. Firstly, Newtonian dynamics can be cleverly derived to yield an inevitable description that can be directly applied in a translational (non-rotating) reference frame by applying Newtonian dynamics to the reference object of the reference frame. Therefore, the theoretical expression for inertial forces is obtained through the real force acting on the reference object. Secondly, the traditional form of Newtonian dynamics can in principle be generalized to any translational reference frame and still holds by simply replacing the force terms from full to relative forces. Thus, it leads to a new approach for calculating the work done by the inertial force. Finally, as a check, the typical pedagogical topic of work done by inertial forces was re-examined and self-consistent results were obtained.  Related Articles | Metrics | Comments（0）

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Berry curvature in solid state physics YUAN Zhe, ZHOU Shi-ming College Physics    2024, 43 (5): 1-.   DOI: 10.16854/j.cnki.1000-0712.230289 Abstract （1004）      PDF（pc） （808KB）（954）       Knowledge map    Save Periodic potential and Bloch,s theorem in solid makes Berry curvature different from that in continuousmedia. The Bloch wave function of the n-th energy band at k point in Brillouin zone has its modulation factor unk(r), and the corresponding Berry curvature is given by Ωnk=×Ank with Berry connection Ank=〈unk|ik|unk〉. In the presence of inversion and time reversal symmetries, Berry curvature vanishes at in any k point of Brillouin zone. With broken inversion and time reversal symmetries, or with spin-orbit coupling, or the band degeneracy, Berry curvature can be nonzero. Berry curvature induces an anomalous velocity perpendicular to external electric field, which in turn leads to the intrinsic anomalous Hall effect, the intrinsic spin Hall effect and the nonlinear Hall effect. This work is helpful for a better understanding of Bloch wave function and Boltzmann transport equation. Related Articles | Metrics | Comments（0）

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The four distinct comings of Planck's constant h CAO Ze-xian College Physics    2024, 43 (11): 1-.   Abstract （951）      PDF（pc） （1040KB）（496）       Knowledge map    Save Planck’s constant h, the tag of quantum theory, is one of the universal physical constants. The various distinct comings of Planck’s constant include the derivation of Plank’s spectral distribution formula for black-body radiation, Einstein’s interpretation of the experimental results concerning photoelectric effect, quantization of phase space by Planck (and also by Bohr and Bose), and Schrdinger’s effort to rescue the unified theory of gravity and electricity by Weyl, in which the role of the constant h is either simply a prefactor to make hν of the same dimension as energy or to make hν/kT dimensionless, a quantum of action per se,the volume element of the phase space or the angular momentum, or the energy quantum for light in the form of h , or a factor in the wave theory in the form of ih or i.The distinct comings of the Planck’s constant in the quantum theory rightly justifies its universality.By the way, neither Planck nor Einstein had introduced any revolutionary ideas by applying the energy quantum  h. Related Articles | Metrics | Comments（0）

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Discussion on some problems of solar cells ZHANG Zhi-ming1, 2, HE Shan1, SUN Tie-tun3 College Physics    2024, 43 (5): 25-.   DOI: 10.16854/j.cnki.1000-0712.230209 Abstract （720）      PDF（pc） （763KB）（268）       Knowledge map    Save The following three problems on solar cells are studied in this paper： It is well known that the key element of a solar cell is a PN junction. However, the so called current-voltage characteristics curve (I-U curve) of a solar cell looks very differently with that of a normal PN junction, why? How does the I-U curve of a solar cell change exactly? How do the output current, output voltage, and output power of a solar cell change with the load resistance? The study on these problems has important significance in design and application of solar cells. The research results are as follows: The reason of first problem that the so called I-U curve of a solar cell is, in fact, the I-U curve of the load resistance in a solar cell circuit, not the I-U curve of the PN junction in the solar cell. The answerHYPERLINK"javascript:;" to the second problem is that the current monotonously decreases with increasing the voltage. The answerHYPERLINK"javascript:;" to the third problem is that for a solar cell circuit, with the increase of the load resistance, the output current monotonously decreases, and the output voltage monotonously increases, while the output power does not change monotonousl. There exists a maximum output power which correspods to an optimal load resistance. Related Articles | Metrics | Comments（0）

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College Physics    2024, 43 (8): 1-.   DOI: 10.16854/j.cnki.1000-0712.240138 Abstract （719）      PDF（pc） （448KB）（688）       Knowledge map    Save Related Articles | Metrics | Comments（0）

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Derivation ofthe De Broglie matter wave equation WANG Yang College Physics    2024, 43 (5): 22-.   DOI: 10.16854/j.cnki.1000-0712.230226 Abstract （694）      PDF（pc） （762KB）（784）       Knowledge map    Save The equation for the momentum and the wavelength for the matter wave is derived in two intuitive ways. The first way is to use the Lorentz transformation to obtain the inherent time difference between the head and tail of the moving particles, and then obtain the corresponding wavelength for the material wave through its phase difference and the length of the particle occupied in space. The second way is to obtain the equation by calculating the traveling wave adapted to the phase change of the particle. These two derivation methods are intuitive and helpful to beginners to understand the physical image of the matter wave. Related Articles | Metrics | Comments（0）

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Attosecondpulse laser and electron dynamics-interpretation of Nobel Prize in Physics 2023 WEI Bo-ning1, 2, WANG Li-feng3 College Physics    2024, 43 (11): 7-.   DOI: 10.16854/j.cnki.1000-0712.240349 Abstract （644）      PDF（pc） （1056KB）（756）       Knowledge map    Save The Nobel Prize in Physics 2023 was awarded to three experimental physicists, for their tremendous contribution to "experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter". For the significance and applications of attosecond pulse laser, this paper is organized by the development of human exploration on ultrafast dynamics, the principle and experimental methods of generation and measurements of attosecond pulse laser, typical applications of attosecond pulse laser and future perspectives. Related Articles | Metrics | Comments（0）

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Educational expansion in magnetic charge and its field FU Chun-e1, WEI Shao-wen2 College Physics    2024, 43 (8): 7-.   DOI: 10.16854/j.cnki.1000-0712.230355 Abstract （623）            Knowledge map    Save In physics, due to the symmetry between electricity and magnetism, physicists believe that magnetic charge exist in nature, similar to electric charges. Although experimental evidence for the existence of magnetic charges has not been found, discussion and exploration of this concept have never ceased. The initial focus of this article is to study the covariant form of the Maxwell's equations in the presence of magnetic charges. To do this, we classify the magnetic field into two types, i.e., Bh generated by magnetic charges and Bt produced by changing electric fields and conduction currents. Then we find that by introducing certain constraints for Bh, we can decompose the Maxwell's equations into the Maxwell's equations without magnetic charges and three additional constraint equations satisfied by Bh. The Maxwell's equations without magnetic charges naturally satisfy the principle of covariance in specail relativity theory, and we will not talk about this. We will study the properties of magnetic charges and their magnetic fields as a new form of matter by the three equations concerning Bh. Related Articles | Metrics | Comments（0）

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Exploration and practice of flipped classroom teaching in college physics  under the background of ideological and political education ——Taking "optical instrument resolution ability" as an example ZHANGYing, LIU Wen-po, LIU Hong-peng, YANG Xiong College Physics    2024, 43 (06): 46-.   DOI: 10.16854/j.cnki.1000-0712. 230342 Abstract （600）      PDF（pc） （1216KB）（638）       Knowledge map    Save In this article the flipped classroom teaching mode is focused. Teaching design is carried out with combining with three-stage teaching method and revolving pre class learning, in class discussion, and post class expansion. It deeply explores the design ideas of online content for pre class learning and the way it connects with the physical classroom. Integrating ideological and political elements into the curriculum through traditional culture, life cases, and hot events, makes abstract physical concepts more vivid, intuitive, and practical. With this plan, the class title rate, student participation, and the rate of correct answers to questions have been greatly improved, Through a survey questionnaire, the feasibility of teaching models, teaching methods, and content feasibility are investigated to assess student recognition. It is found that student recognition is extremely high, and this plan has certain reference value for improving teaching quality. Related Articles | Metrics | Comments（0）

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Exploring the schematic diagrams related to Nernst’s equation SU Shan-he, CHEN Jing-yi, CHEN Jin-can College Physics    2024, 43 (8): 10-.   DOI: 10.16854/j.cnki.1000-0712.230378 Abstract （553）      PDF（pc） （495KB）（191）       Knowledge map    Save It is pointed out that the various schematic diagrams related to Nernst’s equation in textbooks are not equivalent, some of which are acceptable, some are imperfect, and some are incorrect. Moreover, the complete schematic diagrams related to Nernst’s equation are given to remedy the deficiencies in many textbooks. The results obtained are helpful to deepen the understanding of Nernst’s equation and low-temperature chemical reactions. Related Articles | Metrics | Comments（0）

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Fluid mechanics analysis of the formation process of the tip of ice-cream JIN Zi-lu, LU Shen-yi, PENG Shi-xiang College Physics    2024, 43 (11): 74-.   DOI: 10.16854/j.cnki.1000-0712.240015 Abstract （551）      PDF（pc） （828KB）（247）       Knowledge map    Save Based on Poiseuille’s theorem, the formation model of ice cream is established to explain the phenomenon that the tip of the cone produced by the ice cream machine often forms a pointed protrusion. We assume that the raw material of ice cream is a homogeneous, incompressible, but viscous fluid. After analyzing the temperature change during the production process and operator’s manipulation, we confirm the rationality of the hypothesis of the formation model. Using computer simulation software to simplify the model, the formation process of the tip of the ice cream is concluded, that is, the ice cream is subjected to the least viscous resistance in the center of the flow tube, and it is easier to fall than other positions, and finally the tip of the ice cream is formed. The establishment of this model and the exploration of the principle can better understand and apply the principle of fluid mechanics, better understand the phenomena in life and promote the progress of industrial production. Related Articles | Metrics | Comments（0）

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Slant motion considering air resistance YANG Yang College Physics    2024, 43 (12): 11-.   DOI: 10.16854/j.cnki.1000-0712.240086 Abstract （548）      PDF（pc） （902KB）（251）       Knowledge map    Save Considering air resistance and buoyancy, the law of slant motion of the object is studied by numerical solution, including the relationship between range and projecting angle, the relationship between the optimal projecting angle. In addition, the relationship between projecting angle and maximum motion height as well as motion time are also studied. Related Articles | Metrics | Comments（0）

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Deep discussion about a mechanics problem of Chinese Physics Olympiad ZHOUZhi-wu1, LIUWen-biao1, 2 College Physics    2024, 43 (11): 16-.   DOI: 10.16854/j.cnki.1000-0712.240109 Abstract （545）      PDF（pc） （591KB）（299）       Knowledge map    Save Starting from a mechanics problem of Chinese Physics Olympiad, this paper delves into the motion of a slider on a smooth hemisphere under the influence of gravity. Beginning with a straightforward application of conservation laws to address the original query, this paper proceeds to derive the slider’s dynamic equations through force analysis using Newtonian mechanics. Furthermore, an analysis is carried out from the perspectives of Lagrangian and Hamiltonian mechanics, as well as the weak field approximation of general relativity, deriving dynamic equations consistent with those obtained via Newtonian mechanics. Numerical solutions are then employed to solve the dynamic equations, allowing for the visualization of the slider’s trajectory. Finally, a comparison is made between the trajectory of the slider’s motion on the smooth hemisphere under gravity and that on a vertical smooth conical surface. Related Articles | Metrics | Comments（0）

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Proving the uniqueness theorem of electromagnetostatic  field by applying action HUANG Zhen-rui, Shi Huan-yu MIAO Rong-xin College Physics    2024, 43 (8): 13-.   DOI: 10.16854/j.cnki.1000-0712.230423 Abstract （544）      PDF（pc） （514KB）（212）       Knowledge map    Save  The uniqueness theorem of the electrostatic field plays an essential role in electrodynamics. It states that the electric field can be determined uniquely, given the charge distribution and dielectric distribution of the area of our concern and given the potential or its normal derivative on the boundary. The proof of uniqueness theorem is tricky. However, most textbooks do not discuss the proof method's physical significance and the generalization to other fields. This paper finds that the action closely relates to the proof of uniqueness theorem. Once one constructs the action obeying the corresponding equations of motion and boundary conditions, one can prove the uniqueness theorem for any field. Furthermore, we discuss more general equations of motion and boundary conditions and study the case violating the uniqueness theorem. Related Articles | Metrics | Comments（0）

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Evaluating summation of series with the resdue calculus YANG Shi-jie College Physics    2024, 43 (8): 4-.   DOI: 10.16854/j.cnki.1000-0712.230445 Abstract （541）      PDF（pc） （518KB）（614）       Knowledge map    Save  By employing the Bose and Fermi distribution functions, we introduce a method to calculate the summation of an infinite series via the residue calculus. With this method we obtain several infinite series sums and further derive the Mittag-Leffler expansions of some important functions. Related Articles | Metrics | Comments（0）

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Measuring the diameter of superfine wire by laser diffraction LIU Jun, ZHOU Rong-hao, ZHAO Song-qing College Physics    2024, 43 (7): 46-.   DOI: 10.16854/j.cnki.1000-0712.230376 Abstract （537）      PDF（pc） （679KB）（268）       Knowledge map    Save Based on the principle of laser diffraction, a method of measuring the wire diameter which is less than 12μm is introduced. Using the least square method fitting the diffraction intensity of the central bright stripe, the wire diameter can be obtained in high-precision. Carbon fiber and Xinjiang long-staple cotton are used as samples, and three lasers with different wavelength are used to carry out the experiment. It is realized that accurate experimental results can also be obtained by using low precision teaching light intensity detectors and smart phone light sensors. Related Articles | Metrics | Comments（0）

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Notes on Retarded and Advanced Green's Function WANG Zi-hao, MENG De-shuo College Physics    2024, 43 (11): 78-.   DOI: 10.16854/j.cnki.1000-0712.230396 Abstract （485）      PDF（pc） （575KB）（142）       Knowledge map    Save  Based on the theory of complex variable function and the basic laws of electromagnetic phenomena, the Lorentz invariant form of the propagator function in quantum electrodynamics is studied first, and the relationship between the propagator function and the delayed and advanced Green function is discussed. Secondly, the delayed and advanced Green's functions are derived by Fourier transform and the properties of ordinary differential equations combined with the boundary conditions. The infinitesimal imaginary part is added to the wave number again and applied to the Fourier transform. The result is reproduced in a more rigorous and simple way by combining the residue theorem and the equivalent lemma. Finally, the specific expression of the Fourier-Laplace integral theorem is given. It provides a new idea for the teaching and research of electrodynamics. Related Articles | Metrics | Comments（0）

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A study on the free falling motion of raindrops with a diameter of 5 mm in still air at 20 ℃ SHAO Yun College Physics    2024, 43 (04): 56-.   DOI: 10.16854/j.cnki.1000-0712.230185 Abstract （480）      PDF（pc） （791KB）（334）       Knowledge map    Save The article adopts the spherical raindrop model and uses the strict expression of the air resistance coefficient CD, namely the Wallis formula, to calculate the v~t image of a raindrop with a diameter of 5 mm when it freely falls from rest in still air at 20 ℃. The article also solves the analytical and universal v(t) function under the approximation of CD being uniformly taken as 0.44, and produces the corresponding v~t image. The results show that these two v~t curves almost completely coincide, indicating that the approximate treatment is completely appropriate. The article explains the reason for this and points out the reason for the limit rate measured in the experiment is 2.00 m/s lower than the theoretical value under the spherical raindrop model is the actual raindrop shape presents a Hamburg shape, and its actual air resistance coefficient is calculated to be about 0.52. We believe that the spherical raindrop model is generally practical. Related Articles | Metrics | Comments（0）

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Method for measuring Young’s modulus by replacing optical levers with optical interference and diffraction devices WANG Guo-you, FAN Qin, ZI Xiong, ZHU Wen-yi, CHEN Guang-wei, CHEN lang College Physics    2024, 43 (04): 44-.   DOI: 10.16854/j.cnki.1000-0712.230126 Abstract （478）      PDF（pc） （1146KB）（450）       Knowledge map    Save A Young’s modulus experimental instrument is designed based on the principles of light interference and single-slit diffraction. According to the change rule of fringes of light interference and diffraction, the tiny length change of metal wire under tension can be measured, and then the high precision measurement of Young’s modulus of metal wire is realized. To satisfy the experimental conditions for interference of light, a pneumatic tension adjusting device is designed to replace weights, in which the shaking problem of the instrument is solved and the stepless adjustment of tension change and the reading of tension directly from the electronic scale are realized. The instrument also make a simple traditional mechanical experiment change into a comprehensive experiment combining mechanics and optics for measuring Young’s modulus, which enriches the experimental content, broadens the students’ vision, and improves their comprehensive ability to analyze and solve problems. Related Articles | Metrics | Comments（0）

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Study on exact classical and quantum dynamics of two coupled driven harmonic oscillators CHEN Kang-kang, LI Hai-feng, OU Zhi-min, ZHANG Kai-feng College Physics    2024, 43 (04): 22-.   DOI: 10.16854/j.cnki.1000-0712.230193 Abstract （477）      PDF（pc） （746KB）（464）       Knowledge map    Save The harmonic oscillator model, which can be analytically solved, takes an important part in physics and is a powerful theoretical model for describing many physical processes. However, the research on driven harmonic oscillator is rarely involved. In this paper, we study the exact classical and quantum dynamics of two coupled harmonic oscillators in the driving external fields. In the framework of classical mechanics, the exact energy values of the time-dependent external fields acting on two coupled harmonic oscillator systems are obtained by virtue of the Hamiltonian canonical equations. If the driven fields are constant, the energy eigenvalues and eigenstates of the system in quantum mechanics are attained. In consideration of the time-dependent driven fields, the expected energy values and wave function of quantum system are derived using operator algebra methods. Because the microscopic particles have wave-particle duality within the framework of quantum mechanics, there are obvious differences between the classical and quantum dynamics for the system consisted of the two coupled harmonic oscillators in the external driving fields. Related Articles | Metrics | Comments（0）