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Table of Content

    28 July 2022 Volume 41 Issue 07
      
    Transverse vibration of thin plate with circular or sector shape(II) Separation of variables of partial differential equation in the problem of transverse vibration of sector plate
    WU Chong-shi
    College Physics. 2022, 41(07):  1.  doi:10.16854/j.cnki.1000-0712.210539
    Abstract ( 640 )   PDF (198KB) ( 322 )  
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    The transverse vibration of sector plate is discussed from the point of view of equations of mathematical physics. The separation of variables applied to the partial differential equation in the eigenvalue problems is sketched. As an example, the eigenfrequencies and corresponding proper vibration modes are given when the boundary of sector plate is fixed.

    Are there limits to electrostatic equilibrium and electrostatic shielding?
    LI Zu-bin, ZHAO Xin, SONG Feng
    College Physics. 2022, 41(07):  4.  doi:10.16854/j.cnki.1000-0712.210533
    Abstract ( 854 )   PDF (588KB) ( 446 )  
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     Electrostatic equilibrium and electrostatic shielding are important knowledge points in electromagnetics. The key point is that there are a large number of free electrons in the conductor, which are form a new charge distribution under an external electric field. The resulting additional electric field offsets the external field and makes the electric field inside the conductor zero everywhere. Then, if the external electric field continues to increase, can electrostatic equilibrium and electrostatic shielding be realized all the time? Are there limits to electrostatic equilibrium and electrostatic shielding? This paper analyzes the process of electrostatic balance from the
    Propagation characteristics of Laguerre-Gaussian beams in high-speed moving layered media
    WANG Ming-jun, WANG Wan-rou, ZHANG Ying, KE Xi-zheng
    College Physics. 2022, 41(07):  8.  doi:10.16854/j.cnki.1000-0712.210302
    Abstract ( 553 )   PDF (348KB) ( 549 )  
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    The vortex beam has special dynamics and quantum properties, so it has great research value in the field of communication and medicine. These properties are closely related to its unique phase structure. With the deepening of research, the propagation characteristics of vortex beams in the medium have also received extensive attention. This paper mainly studies the phase characteristics of vortex beams in layered media. Taking the linearly polarized vector Laguerre-Gaussian beam as an example, according to the method of transmission matrix, wave decomposition and Lorentz transformation, we analyze its phase change in free space, single-layer medium, high-speed moving medium and multi-layer medium. It is found that the phase rotation direction of the reflected vortex beam and the transmitted vortex beam is related to the wave vector, and the phase structure will change with the change of the incident angle.

    Applying the momentum theorem of particle system to solve the motions of soft chain
    SHAO Yun
    College Physics. 2022, 41(07):  13.  doi:10.16854/j.cnki.1000-0712.210500
    Abstract ( 915 )   PDF (280KB) ( 899 )  
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     In this paper, three kinds of soft chain motions are solved by using the momentum theorem of particle system, and their respective characteristics are revealed. At the same time, it is shown that the advantages of the method of momentum theorem lie in the protruding physical thought and the concise calculation process. The specific characteristics of the third motion are analyzed and calculated step by step by iterative method, and the main motion characteristic parameters are used to describe the successive attenuation oscillation of the chain. The necessary diagrams, demonstrations and explanations are given, and some regularity are found. In addition, a practical so-called “dynamic equation of tangential motion of chain particle system” is proposed.

    The critical angular velocity of a rotating spring on a horizontal plane
    ZHAO Dong-qiu, JIA Shuan-wen, QIN Xu-ming, YUAN Di, DONG Hao
    College Physics. 2022, 41(07):  19.  doi:10.16854/j.cnki.1000-0712.210490
    Abstract ( 633 )   PDF (172KB) ( 266 )  
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     This paper points out the problems existing in the current research of critical angular velocity of rotating spring on a horizontal plane, and gives the physical definition of critical angular velocity of rotating spring. On the basis of deriving the elastic force equation of each point inside the rotating spring, the critical angular velocity and critical length formulas of the rotating spring are deduced from the definition. Then the related problems are discussed.

    Improvement and error correction of “Solution of the electric field line equation in two-dimensional complex electrostatic field and numerical simulation”
    ZHOU Qun-yi, ZHOU Li-li, MO Yun-fei, HOU Zhao-yang, LIU Tian-gui
    College Physics. 2022, 41(07):  22.  doi:10.16854/j.cnki.1000-0712.210608
    Abstract ( 430 )   PDF (413KB) ( 405 )  
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    The advantages of literature has been confirmed, some formulas that need improvement have been suggested, the errors of two formulas have been pointed out, and then the correct formulas have been proposed, which have been verified with MATLAB graphics.

    Research on theory and simulation of electrostatic shielding effect
    HUANG Yan-qing, ZHANG Ding-zong, WANG You-wen, WU Fa-mei
    College Physics. 2022, 41(07):  28.  doi:10.16854/j.cnki.1000-0712.210479
    Abstract ( 916 )   PDF (301KB) ( 523 )  
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     For the electrostatic shielding effect, the electric field inside the metal shell is not affected by that outside the shell whether the metal shell is grounded or not. However, it cannot be obtained directly from Gauss theorem that the electric field outside the shell does not affect the electric field at any position inside the shell. In this paper, the electrostatic shielding effect is proved strictly by the uniqueness theorem of electrostatic field. In addition, the electrostatic shielding effect is further verified by numerical simulation. For example, the electric potential of the metal shell changes with the external electric field, which results in the change of the overall electric potential inside the shell while the electric field does not change. Finally, the distribution of the induced charge in the grounded metal shell is numerically calculated, and a large surface density of charge is generated when the metal tip is near the charged objects.

    Research on equivalent transformation for accompanied sources between star and delta connection
    WAN Kai, SHEN Yi-qi,
    College Physics. 2022, 41(07):  32.  doi:10.16854/j.cnki.1000-0712.210520
    Abstract ( 632 )   PDF (331KB) ( 225 )  
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    This paper proposes an efficient method for accompanied sources’ equivalent transformation between star and delta connection. In the deduction, we adopte the comprehensive application of equivalent transformation between accompanied current and voltage sources, the transfer of unaccompanied source, and special treatment of resistances with values of 0 and ∞ Omh. The expansion of equivalent transformation analysis from the active series and parallel circuit to active star and delta connected circuit provides a convenient analysis for practical circuit. 

    Analysis and calculation of inductance coefficient of circular coil with rectangular section
    ZHANG De-gen, WANG Min-zhu
    College Physics. 2022, 41(07):  36.  doi:10.16854/j.cnki.1000-0712.210519
    Abstract ( 954 )   PDF (258KB) ( 688 )  
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    The inductance coefficient of a multilayer tightly wound rectangular circular coil is divided into self-inductance of all single-turn coils and mutual inductance of any two coils, and then the sum of all self-inductance and mutual inductance of the entire winding is obtained. Using Neumann formula and numerical integration software, the inductance coefficient of the multilayer close-wound rectangular section circular coil with an average radius of 10 cm is calculated to be 4.65 mH, while the inductance coefficient of the actual coil with the same size measured by inductance meter is 4.66 mH. The theoretical calculated value is basically consistent with the experimental measured value, and the relative error of the two is only 0.22%. It provides theoretical reference for designing inductance coil.
    Analysis of grating diffraction based on Fourier transform
    WANG Yi-quan, ZHANG Ying, CHEN Xiao, ZOU Bin, WANG Qiong-qianhui, LI Chuan-bo, PENG Hong-shang, LI Yi-yi
    College Physics. 2022, 41(07):  39.  doi:10.16854/j.cnki.1000-0712.210495
    Abstract ( 817 )   PDF (550KB) ( 331 )  
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     Based on the diffraction characteristics of cosine gratings, Fourier analysis is applied to discuss the diffraction pattern of a transmission grating. The diffraction field is the same as the grating diffraction law obtained by the traditional interference diffraction analysis method. The quantitative relationship between grating diffraction field and grating structure is summarized, and a unified method for analyzing grating diffraction is concluded, which is significant for students to correctly understand grating diffraction.

    Application of firstprinciples to crystal structure teaching of solid physics
    YU Yang
    College Physics. 2022, 41(07):  43.  doi:10.16854/j.cnki.1000-0712.210485.210485
    Abstract ( 740 )   PDF (255KB) ( 663 )  
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    Crystal is a fundamental and important concept in solid state physics. But the reason why different element crystals present different crystal types, such as face centered cubic (fcc), body centered cubic (bcc), hexagonal dense packing (hcp), and even simple cubic structure (sc), is not explained in the course. In this paper, the single point energy of metal crystals such as polonium (Po), tungsten (W), aluminum (Al) and magnesium (Mg) is calculated by using the density functional theory and the first principle software quantum Espresso. The energy curves varying with the lattice constant under different crystal structures are obtained. The theoretical lattice structure of each metal crystal is discussed, and the problem of different crystal types of different solid crystals is explained.

    The difference between quantum uncertainty relation and  noise-disturbance uncertainty relation
    ZHENG Xiao, ZHANG Guo-feng
    College Physics. 2022, 41(07):  46.  doi:10.16854/j.cnki.1000-0712.210455
    Abstract ( 463 )   PDF (222KB) ( 392 )  
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    Quantum uncertainty relation and noise-disturbance uncertainty relation are two different concepts, which are the foundational difference between classical and quantum mechanics. This paper reviews the development of quantum uncertainty relation and noise-disturbance uncertainty relation, and introduces the differences between them, hoping to promote the development of quantum uncertainty relation and noise-disturbance uncertainty relation in the future.

    Diagonalization of Lorentz transformation matrix and its significance
    LI Yi-jie, ZHANG Cheng-yuan, SHI Wei, KANG Xiao-shen, GONG Li, XU Guang-zhi
    College Physics. 2022, 41(07):  51.  doi:10.16854/j.cnki.1000-0712.210522
    Abstract ( 1051 )   PDF (157KB) ( 714 )  
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    The significance of eigenvectors and eigenvalues of Lorentz transformation matrix in the process of diagonalization are discussed. The procedure of diagonalizing Lorentz transformation matrix is to transform the general inertial frame of reference into the light-cone coordinate system. The eigenvectors are the vectors on the axis of light-cone coordinate system. The eigenvalues correspond to the scaling factor for the light-cone coordinate components under the reference frame transformation. This paper can help students to deepen their understanding of Lorentz transformation and the space-time characteristics of special relativity.

    Measurement of sound speed based on nearly complete destructive interference of ultrasound
    YAN Zhi-tao, JING Tian-hui, TAN Tan, XU De-fei
    College Physics. 2022, 41(07):  54. 
    Abstract ( 482 )   PDF (219KB) ( 146 )  
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     An ultrasonic interference device is built in this paper, in which two independent and adjustable wave sources are introduced. One is a fixed wave source and the other is a parallel moving one. With this device, the wavelength of ultrasonic waves can be measured based on nearly complete destructive interference of waves, and then the speed of sound can be measured accurately. This method can be regarded as an improvement in the measuring methods of sound speed in the current experimental course of college physics. And this device can also be used to demonstrate the phenomenon of beats caused by the superposition of two waves of slightly different frequencies.

    Concept of optical memory effect in scattering medium imaging and its progress#br#
    WANG Yu-ji, ZHOU Xin, BAI Xing, YANG Zhong-zhuo, YU Zhan, CHEN Xing-yu
    College Physics. 2022, 41(07):  58.  doi:10.16854/j.cnki.1000-0712.210433
    Abstract ( 994 )   PDF (252KB) ( 786 )  
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    Obtaining the information of the target object through an opaque scattering medium is one of the important research topics in the field of optical imaging.The concept of optical memory effect has provided strong support for the research of scattering medium imaging,and has promoted the development of various practical scattering imaging technologies.However,the concept of optical memory effect is mainly proposed on the basis of incident light rotation or spatial translation,and the scattered imaging methods developed on this basis have many limitations such as small imaging range.In this paper,the physical meaning of the concept of optical memory effect is introduced,and the development of the concept is reviewed since it was first proposed from the perspective of spatial translation,and then gradually developed to cover the spatial domain and spectral domain.A prediction is made that the concept will further develop to the spatio-temporal range and becomes an important index helpful to comprehensively describe the spatio-temporal characteristics of point spread function.And the concept of generalized optical memory effect is put forward to provide a new idea for the in-depth study of correlation scattering imaging technology.

    Physics of animal orientation and navigation
    ZHOU Xu-bo, QIU Li-peng, LONG Yun-ze
    College Physics. 2022, 41(07):  63.  doi:10.16854/j.cnki.1000-0712.210560
    Abstract ( 523 )   PDF (179KB) ( 144 )  
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    Abstract:Different kinds of animals can orient and navigate based on different principles.In this paper,echolocation in bats,geomagnetic orientation in birds and orientation of polarized light in insects are briefly reviewed.Environmental changes and human disturbance can affect animal navigation.The principles of animal orientation can inspire humans,and some research results have been applied in peoples production and life.

    A network live broadcast and remote experiment merged with robot vision
    WANG Ye
    College Physics. 2022, 41(07):  68.  doi:10.16854/j.cnki.1000-0712.210384
    Abstract ( 389 )   PDF (379KB) ( 323 )  
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    A network live broadcast technology and remote-controlled experimental system of Michelson interference experiment merged with robot vision is realized.The remote-controlled experiment teaching mode and method merged with robot vision are studied.The interference fringe images and data are transmitted in real time in the way of machine broadcast.The remote control and automatic measurement of the experiment are carried out by mobile platform and client or network user.The system and method will strengthen the network live broadcast and the remote experiment more on-site and operable.

    Visualization of Fresnel ultrasonic lens experiment
    LI Ze-you, ZOU Cao-yi, YU Qi-pan, LI Si-qing, LUO Duan-bin
    College Physics. 2022, 41(07):  73.  doi:10.16854/j.cnki.1000-0712.210484
    Abstract ( 483 )   PDF (240KB) ( 130 )  
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    Fresnel ultrasonic lenses with different focal lengths are designed.The visualization of 40 KHz ultrasonic field distribution passing through a Fresnel ultrasonic lens is realized by using VSchlieren optical path.According to the collimation of sound field distribution after passing through Fresnel ultrasonic lens,the focal length of acoustic lens can be measured in the visualization state like the traditional experiment of measuring the optical focal length.The measurement results of the focal length of acoustic lens by using the experimental device are in well agreement with the design values.The acoustic measurement is completed by optical means,and the combination of optical and acoustic content in college physics experiment is realized.

    Drift phenomena in laser scattering and related numerical simulation method#br#
    XU Lei, LI Ke-yu, GUO Jia-yu, ZHONG Ming
    College Physics. 2022, 41(07):  77.  doi:10.16854 /j.cnki.1000-0712.210447
    Abstract ( 601 )   PDF (402KB) ( 155 )  
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    When a laser beam hits a rough surface,scattered spots are produced.Even though the receiver remains stationary,the collected scatter pattern changes and appears to “drift”.It is found that the main reason for the scattering drift is the phase change of the light due to the heat absorption and expansion of the rough surface,which causes the interference pattern to change.A large amount of experimental data is collected to analyze the dynamics of the scattering using the correlation coefficient and its rate of change.In addition,the scattering drift is also simulated.

    Analysis of β-carotene content in carrot and pumpkin by  resonance Raman mapping
    SHEN Zhao-ting, LIU Sai-yu, ZHANG Yu-xuan, WU Nan-nan, OUYANG Shun-li
    College Physics. 2022, 41(07):  82.  doi:10.16854/j.cnki.1000-0712.210306
    Abstract ( 529 )   PDF (258KB) ( 133 )  
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    Carrots and Pumpkin contain a large number of β-carotene, have a high pharmacological and nutritional value. Because β-carotene contains a large number of delocalized electrons and has photoelectric characteristics, a laser with excitation wavelength of 532 nm can produce resonance Raman effect in the absorption spectrum of β-carotene in Raman scattering. The Raman spectra of carrot and Pumpkin are measured and the image of Raman is made. It is found that the intensity of characteristic Raman peaks of β-carotene in carrot epidermis is higher than that in root core, the intensity of characteristic Raman peaks in the β-carotene of Pumpkin skin is also higher than that in the pulp. This study provides a new method to measure the content of β-carotene by using Raman mapping technique.