Table of Content

    20 March 2021 Volume 40 Issue 3
    Taking electromagnetics as an example to talk about ideological and political education as a fertile soil for students’growth
    WU Xiao-shan, SUN Liang, ZHANG Hai-jun, LIU Jun-ming, XIN Bei
    College Physics. 2021, 40(3):  1-3.  doi:10.16854 /j.cnki.1000-0712.200328
    Abstract ( 2759 )   PDF (914KB) ( 1096 )  
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    How to construct a better course is discussed in this paper by taking“Electromagnetics”as an example.

    It is also discussed how to embed the three elements of“Materialism”,“From practice to practice”,“Seek

    truth from facts”into the course,and let them rooting and germinating in students’mind.

    Study of the elastic potential energy of a spherical body in micro deformation
    YU Feng-jun, TANG Zhen-jie, TIAN Jun-long, ZHANG Xi-wei
    College Physics. 2021, 40(3):  4-7.  doi:10.16854 /j.cnki.1000-0712.200176
    Abstract ( 1210 )   PDF (1192KB) ( 292 )  
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    In this paper,we study the elastic potential energy of an elastic sphere when it is deformed into a

    long rotating ellipsoid while keeping its volume constant. Firstly,the displacement function is determined by the

    principle of minimum potential energy and physical conditions. Then,according to the relationship among elastic

    potential energy density,strain and displacement,the elastic potential energy is obtained by integral calculation,

    and the beneficial discussion is made.

    The size effect of parallel-plate capacitor
    CAO Xiao-ge, YANG Yang
    College Physics. 2021, 40(3):  8-11.  doi:10.16854 /j.cnki.1000-0712.200308
    Abstract ( 1236 )   PDF (875KB) ( 700 )  
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    It is investigated in this paper how the capacitance of parallel circular-plate and rectangular-plate

    capacitors varies with the size,respectively. For each kind of capacitor,first it is assumed that charge is distributed

    uniformly on the plate,then approximate values of capacitance can be obtained conveniently,afterwards more accurate

    values are obtained via finite element simulation using Ansoft. By comparison,it is discovered that results obtained

    using the approximation of uniform charge distribution can reflect correctly the tendancy how the capacitance

    varies with the size,which is better than the capacitance formula of parallel-plate capacitor in textbooks; however,

    those values are smaller,since charge is not strictly distributed uniformly on the plate,but less in the middle and

    more on the edge.

    Motion analysis of positive charge in uniform obliquely intersecting electromagnetic field under non-relativity
    SHAO Yun, XU Shi-ye
    College Physics. 2021, 40(3):  12-18.  doi:10.16854 /j.cnki.1000-0712.200372
    Abstract ( 1001 )   PDF (1016KB) ( 286 )  
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    In this paper,the dynamic vector analysis of the positive charge +q in uniform obliquely intersecting

    electromagnetic field under non relativity is carried out,and the charge’s motion is decomposed into: 1) uniformlyaccelerated linear motion along the direction of magnetic field; 2) uniform linear motion perpendicular to the direction of electric and magnetic field; 3) circular motion with uniform rate perpendicular to the direction of magneticfield. Therefore the complete kinematics equations of electric charge are deduced. Then,the kinematics equations are reduced and simplified,and the projection trajectories of charge in the xy plane under different initial velocities are made and analyzed,of which characteristics and internal reasons are pointed out. An example is given to illustrate the space trajectory of electric charge,and the commonness of it is pointed out. Three special cases of uniform orthogonal electromagnetic field are discussed. In addition,it is pointed out at the end of the paper that the core idea of the method in this paper is the switching of reference frame.

    Analysis of vectors and their vector derivatives in Electrodynamics
    HU Xiang-ming
    College Physics. 2021, 40(3):  19-24.  doi:10.16854 /j.cnki.1000-0712.200167
    Abstract ( 1680 )   PDF (876KB) ( 1615 )  
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    Of all four courses of mechanics,Electrodynamics is thought to be relatively more difficult to learn

    than others by many students.Depending on my own teaching experience,I make a rough analysis about it. It is

    shown that the difficulty lies in whether learners realize the fundamental role of vectors and their vector derivative

    operations. Since Electrodynamics treats both the time evolutions and the local interactions in the electromagnetic

    systems,any part of the course is based on the vectors and their vector derivative operations. Therefore both the

    physical law expressions and the related mathematical calculations are relatively complicated. Only when the

    learners understand the definitions of the vectors and are good at their vector derivative operations will they express

    the physical laws in a reasonable way and understand their applications.

    Application of geometry in solving problems of relativity theory
    FENG Xiao-ming, CHENG Min-xi
    College Physics. 2021, 40(3):  25-28.  doi:10.16854 /j.cnki.1000-0712.200148
    Abstract ( 859 )   PDF (1459KB) ( 304 )  
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    In solving the problems about reference frame transformation in the theory of relativity,it is often required

    to have a long and complicated calculation. Two-inertial-system mapping is often used to transform the computational

    problem into a geometric problem. This method is quick and intuitive but hard for beginners to grasp. To

    express the dynamic process of Lorentz transformation and transfer physical pursuit invariance values,a new geometric

    method named hyperbolic rotation was put forward. Based on the two inertial system mapping,the hyperbolic

    rotation was carried out based on time-interval invariance and the final geometric results were determined by the restriction

    of causality. There was an example to explain the application of two geometric methods in detail.

    Modification of the standing-wave experiment equipment
    MIAO Yong-ping, SUN Er-ping, LI Zhong-li, DAI Kun,
    College Physics. 2021, 40(3):  29-32.  doi:10.16854 /j.cnki.1000-0712.200178
    Abstract ( 1824 )   PDF (722KB) ( 1642 )  
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    The Analysis on the standing wave experiment is carried out. Reasons are found out and then some

    improvements on the experiment equipment are provided. On the one hand,directly measurement of string tension

    instead of the weights is introduced to measure the string tension; on the other hand,a micro-adjustment

    mechanism is assembled to slightly change the length and the tension of string. Thus,experiments on relations of

    string tension,wavelength,frequency and string density can be carried more accurately and conveniently.

    Analysis of the simple pendulum with smartphone magnetic sensor
    WANG Jin-hui, SUN Cun-ying, ZHOU Hong, WANG Yu-xing
    College Physics. 2021, 40(3):  33-37.  doi:10.16854 /j.cnki.1000-0712.200388
    Abstract ( 1694 )   PDF (2305KB) ( 1540 )  
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    The magnetic sensor ( electronic compass) in the smartphone is used to study the magnetic simple

    pendulum based on the Phyphox APP. The results showed that the behavior of magnetic induction with time varies

    with different amplitude angles. Only when the amplitude angle is less than 1°,the simple harmonic vibration of the

    simple pendulum could occur. The curve of magnetic induction via time at different amplitude angles can be described

    by magnetic dipole model combined with large angle pendulum formula. The local gravity acceleration measured

    by the smartphone magnetic sensor is 9.868 m/s2 . Due to the small air damping of the magnetic pendulum,the

    experimental error is only 0.8%.

    The experiment of sound velocity measurement by air column resonance based on simple device
    JIAN Zhi-jian, ZHOU Yan-ming, XIE Zhong
    College Physics. 2021, 40(3):  38-42.  doi:10.16854 /j.cnki.1000-0712.200165
    Abstract ( 1706 )   PDF (873KB) ( 344 )  
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    A simple set is designed to study the resonance of air column and to measure the sound speed. Because

    of the limitation of the simple equipment used in the experiment,the air column is short and thick,so it is

    necessary to consider the endeffect caused by the acoustic radiation of the orifice during the resonance. The experiment

    is easy to be implemented,and the data processing is helpful for training students’ability of mathematical

    modeling,data mining and extraction.

    Optical beat based on microwave frequency difference conversion
    WANG Yun-xin, WANG Da-yong, YANG Deng-cai, LI Ping-xue, RONG Lu, ZHAO Jie
    College Physics. 2021, 40(3):  43-47.  doi:10.16854 /j.cnki.1000-0712.200269
    Abstract ( 934 )   PDF (1152KB) ( 195 )  
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    Optical beat frequency is an important teaching content in college physics and optical experiment.

    Due to the central wavelength drift of the laser,it is difficult to produce observable beat signal in the experiment.

    Inspired by the transformation between electric domain and optical domain in microwave photonic technology,an

    optical beat frequency method based on microwave frequency difference conversion is proposed. By means of intensity

    modulation and phase modulation,two microwave signals with small frequency difference are modulated to the

    same optical carrier. Two stable optical signals with minimum frequency difference are obtained by combining with

    optical filter. Optical beat is realized by using photoelectric detector. Visual low-frequency beat signal is obtained

    by the simulation and experiment. This method provides an experimental scheme for college physics and optical experiments

    combined with the cutting-edge of science. It can expand the teaching content and depth,and can also

    help to cultivate students’scientific literacy.

    Exploration on the online teaching mode of university physics in engineering colleges during the COVID-19 epidemic
    NIU Jin-yan, LIU Jia, MU Li-juan, HE Jian-li, CHEN Wei-li
    College Physics. 2021, 40(3):  48-50.  doi:10.16854 /j.cnki.1000-0712.200426
    Abstract ( 876 )   PDF (2245KB) ( 482 )  
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    In order to meet the online teaching requirements during the COVID-19 epidemic and ensure the implementation of university physics teaching,the online teaching mode is explored in the beginning of this semester. After investigating the characteristics of online teaching on different teaching platforms,it was decided to use Dingding and Rain Classroom as the main teaching software,and the network teaching platform as the teaching resource uploading platform to ensure that students have online resources. Rain Classroom is taken as the unit test and classroom test platform because of its function of data recording and analysis. Through implementing the whole process of the teaching mode of pre - class preparation,live discussion and learning in class,and after - class review,not only the online teaching is effectively carried out,but also the student’s learning data is collected to master the student’s learning situation and provide guarantee for online teaching of university physics.
    Practice of online and offline blending-learning mode of college physics based on the construction of golden course
    WANG Hui, WU Ping, ZHU Hao, ZHANG Xiao, XIE Dong
    College Physics. 2021, 40(3):  51-55.  doi:10.16854 /j.cnki.1000-0712.200379
    Abstract ( 967 )   PDF (1628KB) ( 400 )  
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    In this paper,the teaching reform and practice of online and offline blending-learning mode are

    continued to be carried out in the course of college physics in the recent years. During the practice,according to the

    student-centered education concept and the construction standard of golden course,not only the reform of teaching

    methods based on information technology is carried out,but also the high-level and challenging degree of teaching

    content are improved and the practice of a new teaching mode of knowledge inquiry,speculation,and expansion are

    promoted.Through the design and practice of online and offline blending - learning mode of college physics,

    students’deep and personalized learning is effectively enhanced. In the post-epidemic era,it is of important reference

    value for teachers and students to achieve high-quality online and offline hybrid teaching.

    Improvement of the experiment using a single pendulum to determine gravitational acceleration
    LIU Yu-qi, TAN Yu-sha, WEI Xian-tao, ZHANG Quan, ZHAO Wei, ZHU Ling
    College Physics. 2021, 40(3):  56-61.  doi:10.16854 /j.cnki.1000-0712.200215
    Abstract ( 4174 )   PDF (715KB) ( 597 )  
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    In the experiment of measuring the gravity acceleration by a single pendulum,it is difficult to determine

    the pendulum length very accurately. Under the better measurement conditions,the measurement accuracy

    could generally reach the order of millimeter,and the relative error of the measured gravity acceleration is generally

    about 1%. In order to solve this problem,in this paper the measuring precision was improved to 0.02mm by using

    avernier caliper connected with a cycloid to accurately measure the change of pendulum length instead of directly

    measuring the pendulum length. At the same time,the swing period of the pendulum ball is measured by a photoelectric

    gate,and the different cycloid material and diameter are compared and analyzed.The measurement error of

    acceleration is controlled within 0.1%.

    Dynamic behavior demonstrator of spring pendulum
    HE Yu-ji, WANG Jin-zhi, LIANG Zhuo-fan, LI Qing-feng
    College Physics. 2021, 40(3):  62-65.  doi:10.16854 /j.cnki.1000-0712.200224
    Abstract ( 909 )   PDF (1166KB) ( 354 )  
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    In the non-linear conservative system,the spring pendulum has simple structure and

    typical motion characteristics. In this paper,the motion equation of the spring pendulum system is

    obtained through the theoretical analysis of the Lagrangian equation,and the motion is

    decomposed in the radial and tangential directions. The spring pendulum demonstrator and

    experimental software are designed by using image processing technology to visu- alize the motion

    track and time sequence diagram The trajectory drawn by the software is in good agreement with the

    theoretical results.

    The equilibrium stability of two connected bubbles
    SHENG Tian-shuang¹, YU Qiu-yu²
    College Physics. 2021, 40(3):  66-68.  doi:10.16854 / j.cnki.1000-0712.200184
    Abstract ( 893 )   PDF (797KB) ( 362 )  
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    To study the equilibrium stability of the bubble connecting device,the concept of bubble

    coordinate is introduced.Basedon this,the minimum energy method is used to quantitatively analyze

    the influence of bubble's initial state on bubble's equilibrium stability. The results are in full

    agreement with the qualitative analysis. Mean- while,the experiment shows that the error between

    the results of numerical computation and the experiment results are very small. So the validity

    and accuracy of the equilibrium stability analysis of the bubble connecting device by using the

    minimum energy method are verified.

    An electric dipole and a mechanical pendulum
    JING Yu-wei, WU Pu-xun
    College Physics. 2021, 40(3):  69-71.  doi:10.16854 / j.cnki.1000-0712.200396
    Abstract ( 1093 )   PDF (643KB) ( 712 )  
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    The electric dipole,as one of the basic models of electromagnetism,has an exotic field

    distribution, which in the normal textbooks is given by either the gradient of the

    electric potential or the vector superposition method. These mathematical approaches are

    hardly helpful for students to understand the features and the unique picture of the

    dipole field distribution. Here,based on an analog of the mechanical pendulum and the

    electric di- pole,we give the two forms of the dipole field,especially the free-of-coordinate

    one,and practical applications of this analog. Our paper can benefit beginners in seeing the inner

    relation of knowledges,understanding the features of the dipole,and appreciating the power of

    analogy thinking.

    Influence of interference on optical properties of ITO films
    LIU Zi-jian, ZHAO Ya-li, LI Xiao-yun, LUO Xiang-yu
    College Physics. 2021, 40(3):  72-78.  doi:10.16854 / j.cnki.1000-0712.200222
    Abstract ( 1254 )   PDF (1264KB) ( 446 )  
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    In order to reveal the influence of ITO film thickness on optical transmittance

    and colouration,the visible transmittance, average transmittance and the transmittance

    at 550 nm ( the human eyes sensitive wavelength) were calculated by mean of

    TFCalc optical film design software. The influence of thickness and incident angle on the

    transmittance and colouration of ITO films was investigated by the theory of film interference. The

    results suggested that a series of transmission peaks appear with increasing the ITO film

    thickness. With the in- crease of the film thickness,the optical transmittance of ITO films is

    serrated as well as the average transmittance and transmittance at 550 nm. Accordingly,the

    colouration of ITO film changes periodically. When the incident an- gle increases from 30 to 60

    degree,the colouration of the ITO films with thickness of 300 nm changes from dark

    purple to bright purple. The color chart of ITO films was established in this paper,which provides

    technical support for industrial control and improvement of colouration of ITO films.

    Solving the Schrodinger equation with the relaxation method
    LIU Guan-fu, YU Cong
    College Physics. 2021, 40(3):  79.  doi:10.16854 / j.cnki.1000-0712.200219
    Abstract ( 1197 )   PDF (1415KB) ( 295 )  
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    The most common method to solve ordinary differential equations is the shooting

    method based on Runge Kutta method. The shooting method is commonly used,but the calculation

    time is long. When the boundary conditions are more complex or more sensitive,the relaxation

    method is better.In this paper,the Schrodinger equa- tion is solved by the relaxation method and

    compared with the analytical solution. It is found that the numerical so- lution obtained by

    relaxation method is in good agreement with the analytical solution,and the accurate solution can

    be obtained quickly by relaxation method.