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    18 July 2024 Volume 43 Issue 06
      
    Time-reversal invariance in the quantum wolrd
    YANG Shi-jie
    College Physics. 2024, 43(06):  1.  doi:10.16854/j.cnki.1000-0712.230330
    Abstract ( 198 )   PDF (443KB) ( 249 )  
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    By comparing the similarity of diffusion equation and the Schrödinger equation, the paper addresses the time-reversal invariance of the physical equations. Although the diffusion of a quantum wavepacket exhibits the same characteristics as the classical particles, it is essentially different. The diffusive matter wave remains diffuse even though the time is reversed while the time-reversal invariance holds. As two wavepackets overlap, it reveals the phenomenon of interference.

    On Nernst's theorem and heat capacity statement at absolute zero temperature
    SU Shan-he, CHEN Jin-can
    College Physics. 2024, 43(06):  3.  doi:10.16854/j.cnki.1000-0712.230208
    Abstract ( 115 )   PDF (438KB) ( 98 )  
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    It is proved that the Nernst theorem can be directly used to derive the heat capacity statement at absolute zero temperature, i.e., when the temperature approaches absolute zero, the various heat capacities of thermodynamic systems under different constraints tend to zero. Moreover, the errors in some literatures discussing related issues are pointed out. The results obtained are helpful to the deep understanding of the relationship between the Nernst theorem and the heat capacity statement at absolute zero temperature. 

    Talk about wave speed and wave length  transformation and its physical significance
    ZHOU Qiang, SHEN Qing-hui, LIU Jing
    College Physics. 2024, 43(06):  6.  doi:10.16854/j.cnki.1000-0712.230413
    Abstract ( 180 )   PDF (476KB) ( 205 )  
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    Regarding wave speed and wavelength transformation, although it has been discussed in some literatures, but the obtained expressions is too complex to be remembered, and its physical significance is not involved. This article analyzes this problem by the Lorentz transformation of four-dimensional wave vector, through introducing the concept of wave speed factor and comprehensive velocity factor, the simple expressions that are easy to remember is obtained, and strive to clarify its physical significance, and finally explain its application.

    Thermal entanglement of a two-qubit Heisenberg chain
    MA Ling-yu
    College Physics. 2024, 43(06):  9.  doi:10.16854/j.cnki.1000-0712.230218
    Abstract ( 87 )   PDF (623KB) ( 102 )  
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     Quantum entanglement, as one of the most basic and important physical resources, has shown great practical application prospect in quantum computation and quantum information, and is the foundation of modern quantum computer. In the acquisition of entangled state, some external factors, such as electromagnetic field, temperature and so on, will affect the entanglement state in different degrees. In this paper, the thermal entanglement of the spin-Heisenberg model is calculated by using two different entanglement measures: Concurrence and Negativity.



    Analysis of the absoluteness of event in special relativity teaching——Take the “simultaneous paradox” as an example
    LIU Ke1, LI Chun-yan1, DENG Zhi-jiao2, YU Tong-pu1
    College Physics. 2024, 43(06):  12.  doi:10.16854/j.cnki.1000-0712.230176
    Abstract ( 124 )   PDF (469KB) ( 137 )  
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    The relativistic space-time view is the core content of special relativity teaching. Physical event is an abstract conception in the discussion of relativistic motion. The degree of understanding of event and its absoluteness will affect the establishment of students' relativistic space-time view. By introducing a specific case of “simultaneous paradox” in the teaching of special relativity, this paper emphasizes that the event itself does not depend on the reference frame, and the reference frame is just used to describe the spatio-temporal coordinate of events, which helps students to understand the absoluteness of event and establish the relativistic space-time view.


    Improvement of external scanning measurement method in continuous  field scanning nuclear magnetic resonance experiment 
    HUANG Shui-ping, QIAN Xiao-qing
    College Physics. 2024, 43(06):  16.  doi:10.16854/j.cnki.1000-0712.230374
    Abstract ( 96 )   PDF (719KB) ( 102 )  
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    The main reason for the measurement error of transverse relaxation time by external scanning method in continuous field scanning nuclear magnetic resonance experiment is analyzed. The magnitude of the systematic error is quantitatively estimated. On this basis, the corresponding improvement measures are proposed for the measurement of transverse relaxation time in the external scanning method. The position of the resonance signal in the measurement of the full width at half maximum (FWHM) of the resonance signal is calculated. The results show that the system error caused by nonlinear scanning voltage can be effectively reduced by moving the resonant signal to an appropriate position though adjusting the phase of scanning voltage in the measurement of FWHM of the resonance signal. In addition, the calculation of the magnitude of error and the measurement position of resonance signals can make students' deeply understand the transverse relaxation time and external scanning measurement method.


    Virtual simulation platform of Michelson interferometer based on LabVIEW
    ZHENG Wen-li1, CUI Ji-zhao2, CHEN Shuo1, YANG Yu-run3, ZHAO Yi-han1, WANG Wen-lu1
    College Physics. 2024, 43(06):  19.  doi:10.16854/j.cnki.1000-0712.230280
    Abstract ( 169 )   PDF (966KB) ( 193 )  
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    In this paper, a virtual simulation platform of Michelson interference experiment based on LabVIEW software is developed, which can simulate the real Michelson interference experiment and parameters are allowed to be adjusted to visualize the simulation results in real time. At the same time, in order to verify the accuracy of virtual simulation experiment platform, the measurement experiment of light wave wavelength is completed on Michelson interferometer and the virtual simulation platform respectively. The experimental results are compared and analyzed. In addition, the platform can also be used to simulate the relationship between the wavelength of light wave, the intensity of light wave, the thickness of air film and the distribution of interference fringes and light intensity. In the experiment teaching of Michelson interferometer, the virtual instrument can be used directly for teaching demonstration. The characteristics of fringe distribution and light intensity distribution under different conditions can be shown. The platform realizes the combination of experiment and theory and helps students to learn the use of basic optical instruments, to master the operating procedures of optical experiments, and then the goal of improving the teaching effect can be achieved.

    The Nobel Prize in Physics related to cosmic rays
    College Physics. 2024, 43(06):  25.  doi:10.16854/j.cnki.1000-0712.230371
    Abstract ( 109 )   PDF (770KB) ( 176 )  
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    Cosmic rays are high-energy particles from space and are the only samples of matter from outside the solar system that humans can obtain, including nuclei, electrons, photons and neutrinos, as well as other unknown particles that have not yet been detected. They mainly come from cosmic ray sources in space or are the products of cosmic ray interactions with space matter during propagation. In the history of modern physics, the study of cosmic rays plays an important role, and many new particles are first discovered in the study of cosmic rays. As a bridge between the microscopic particles and the macroscopic universe, the study of cosmic rays has made important contributions to both particle physics and astrophysics. This paper focuses on the Nobel Prize in physics won in the process of cosmic ray research, and introduces its experimental principle, experimental instruments and experimental results in detail. 


    Study of the performance optimization of thermoelectric devices under the trade-off criteria
    BAI Long, ZHANG Rong, ZHANG Lei, TANG Jun
    College Physics. 2024, 43(06):  36. 
    Abstract ( 92 )   PDF (628KB) ( 71 )  
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    Thermoelectric devices can realize the direct conversion of heat and electric energy, and have special advantages in the utilization of waste heat and the development of clean energy technology. But, improving the thermodynamic performance of thermoelectric devices has the more practical significance. In this paper, the thermodynamic characteristics of thermoelectric devices are studied by means of trade-off optimization method (also called Ω criterion). On the basis of constructing a trade-off objective function, the expressions of efficiency and coefficient of performance (COP) under trade-off optimization criterion are obtained, and the influence of thermoelectric figure of merit on efficiency COP is explained in detail. In comparison with the maximum power (maximum cooling power) method, it is found that the thermodynamic performance of thermoelectric devices under the trade-off optimization can easily be improved. 

    Practice of ideological and politicaleducation in construction of fantastic found 
    ZHANG Dong, GUO Xia-sheng, ZOU Xin-ye, TU Juan
    College Physics. 2024, 43(06):  40.  doi:10.16854/j.cnki.1000-0712.230305
    Abstract ( 92 )   PDF (701KB) ( 101 )  
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    In this paper, it takes fantastic sound freshman seminar as an example to explore the process of integrating ideological and political education into textbook writing and in-class teaching, stimulating students' interest in acoustic applications and their passion in learning modern acoustics, and building powerful nation of science and technology. The wisdom demonstrated in the application of acoustics in ancient China is integrated into the course to guide students to have a profound understanding of traditional Chinese culture and scientific research, and to ignite students' pride of national inheritance. The vital role of modern acoustics in technological development is emphasized and students sense of responsibility is cultivated. So it can realize the ideological and political education as a link, and truly achieve educating students through the course. Through the design and implementation of fantastic sound freshman seminar, in this paper the integration of academic and ideological political education is delved, and students' innovative spirit and patriotism are cultivated. A reference for subject teaching is provided and students' comprehensive development is promoted.




    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 ( 132 )   PDF (1216KB) ( 163 )  
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    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.


    Using CMOS image sensors on mobile phone to measure spring stiffness coefficient
    HAN Xiao-wen, CAI Gen-wang
    College Physics. 2024, 43(06):  58.  doi:10.16854/j.cnki.1000-0712.230298
    Abstract ( 143 )   PDF (674KB) ( 114 )  
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    Generally there are two methods for measuring the spring coefficient: tension method and harmonic oscillation method. In the traditional stretching method experiments, most indirect measurements are made by adding or subtracting weights. In traditional harmonic oscillation experiments, a photoelectric gate is used to time the period of the spring oscillator. In this article the complementary mental oxide semiconductor (CMOS) image sensor of a smartphone is primarily utilized to measure the position of the oscillator as it varies with time in the harmonic oscillation. The period and damping information are extracted from the image, and thereby the spring coefficient is obtained. After the improvement, the standard deviation and relative error of the experimental data are smaller, which are 0.0037 N/m and 0.26 percent, respectively. The physical image of the weak damping simple harmonic vibration can be observed in detail and the weak damping coefficient in air and water can be measured.


    A new theory of n-order resistor network with feedback circuits
    LIU Ya-hui1, CHEN yun1, TAN Yu1, WANG Hui-ying1, SUN Weng-weng1, TAN Zhi-zhong1, 2
    College Physics. 2024, 43(06):  63.  doi:10.16854/j.cnki.1000-0712.230362
    Abstract ( 92 )   PDF (617KB) ( 92 )  
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    A class of n-order resistor network model with external resistor is studied, and an analytical expression for the equivalent resistance between any two nodes is given to solve a resistor network problem. The method used in the research of the article mainly uses the branch current to establish a difference equation model and a boundary condition constraint equation model, and then solves the difference equation system to derive the equivalent resistance analytical formula. At the end of the article, some special case issues are discussed, and the conclusions of the special case are compared and validated with other relevant results. The research work of this article has a good demonstration role for physics educators to carry out practical and innovative research.


    Analysis of electromagnetic wave refraction in lossy media
    SUN Hao-yi, XIE De-jun, LIU Gang-cheng, ZHONG Fang-chuan, WU Bin-he
    College Physics. 2024, 43(06):  68.  doi:10.16854/j.cnki.1000-0712.230282
    Abstract ( 113 )   PDF (577KB) ( 112 )  
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    The electromagnetic wave after refraction can change its phase propagation direction as well as its amplitude in lossy media. Conventional textbooks usually treat the problem in terms of complex refractive angles or complex wave vectors. However, these complex concepts lack geometrical or physical significance, and the intrinsic relationship between these two treatments is less discussed. In this paper, based on the study of isotropic media,the two methods are discussed in detail and their equivalence is proved from the perspective of refraction angle and Fresnel coefficient. Numerical simulation by the finite-difference time-domain method verifies the reliability of the theoretical analysis. More interestingly, the electromagnetic wave may not change its propagation direction after oblique incidence into a lossy medium. These analyses not only provides a clear understanding of the laws of electromagnetic wave propagation in lossy media, but also helpful on the teaching of electromagnetism.

    Derivation oftheoretical curve of Franck-Hertz experiment
    LU Ke-jia, WANG Shuang
    College Physics. 2024, 43(06):  73.  doi:10.16854/j.cnki.1000-0712.230240
    Abstract ( 190 )   PDF (683KB) ( 271 )  
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    Theoretical prediction models for anode current of Franck-Hertz experiment need to be established urgently. Existing related theoretical works focus on the analysis and interpretation of experimental results, while a small number of theoretical calculation and simulation works either fail to predict the theoretical curve comprehensively, or take too long time. Based on two lemmas and three hypotheses, this paper provides a comprehensive prediction of the theoretical curve within 1 second, and analyzes the reasons for its deviation from experimental results. After introducing corrections of trajectory and passing rate of electrons, we obtain the modified curve, which is highly consistent with the experimental result. Our results not only verify the correctness of Bohr's theory, but also can be applied to predicting the anode current of Franck-Hertz experiment within a certain range.

    Research on diffraction effect and phenomenon based on optical disc diffraction system
    LIU Jun-ran, KANGXiu-ying, JING Peng-fei
    College Physics. 2024, 43(06):  79.  doi:10.16854/j.cnki.1000-0712.230297
    Abstract ( 152 )   PDF (817KB) ( 137 )  
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    Based on the vectorization of grating equation, two-dimensional scope of grating diffraction is extended to three-dimensional space. The predictability of direction of incident light diffracted by optical disc in three-dimensional Euclidean space is quantitatively given. The grating vector is introduced to quantitatively explain the necessity of color line-line structure on the surface of optical disc under the condition of long distance. The spatial light cone is introduced to quantitatively calculate the principal maximum supremum of diffraction, which has a good visualization effect. Combining the dispersion power, overlap phenomenon, deep well effect and parallax angle, in this paper the problem of how to diffract more pure color lines by optical discs is solved, the commonness and difference between CD and DVD is given, and the theory is found to consistent with the experiment result.