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    20 February 2021 Volume 40 Issue 2
      
    The contribution for general relativity and black hole theory by R. Penrose
    ZHAO Zheng
    College Physics. 2021, 40(2):  1-11.  doi:10.16854/j.cnki.1000- 712.200476
    Abstract ( 782 )   PDF (1790KB) ( 272 )  
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    This paper presents the important contribution for general relativity and black hole theory given by R. Penrose who was awarded the 2020 Nobel Prize in physics. That includes the famous singularity theorem,Pen-rose diagram,Penrose process and the cosmic censorship hypothesis. The friendship and co-operation between R.Penrose and S.W. Hawking are introduced. The discovery of a supermassive compact object at the center of our gal-axy by R. Genzel and A. Ghez who were also awarded the 2020 Nobel Prize in physics,is briefly introduced.

    Teaching development of the nonlinear characteristics of forced vibration
    DING Hong-sheng, WANG Jia-xi, ZHANG Shi-ping, DONG Jun-jun
    College Physics. 2021, 40(2):  12-17.  doi:10.16854 /j.cnki.1000-0712.200335
    Abstract ( 635 )   PDF (1739KB) ( 378 )  
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     Forced vibration is an important teaching content in both college physics and college physics experiments.In order to make students understand the nonlinear characteristics of the forced vibration more deeply,the nonlinear correction of the forced vibration equation is carried out based on the nonlinear factors and experimental data involved in the Pohl resonator,and the nonlinear characteristics are discussed by numerical analysis. By introducing the Duffing equation of hard spring type,the evolution of the system from periodic motion to chaotic state is discussed. The relatively stable equilibrium point in forced vibration is compared with the singular attractor to expand the teaching content of nonlinear vibration.

    Study of the range of uniform magnetic field of Helmholtz rings
    MO Yun-fei, ZHOU Qun-yi , HOU Zhao-yang, ZHOU Li-li
    College Physics. 2021, 40(2):  18-20.  doi:10.16854 /j.cnki.1000-0712.200137
    Abstract ( 764 )   PDF (1367KB) ( 191 )  
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     The analytical solutions of the magnetic field of Helmholtz rings in the rectangular coordinate are derived,and they are dimensionless. The components of magnetic field are obtained by means of the complete elliptic integral of first and second kinds. The distribution of magnetic field is plotted by means of MATLAB. It is found that the range of uniform field is octopus shape. Furthermore,the change of the range of uniform field with the distance between two current coaxal rings is discussed

    Discussion on image method within dielectic
    FU Chun-e
    College Physics. 2021, 40(2):  21-22.  doi:10.16854 /j.cnki.1000-0712.200300
    Abstract ( 1072 )   PDF (1077KB) ( 391 )  
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    The method of images is a mathematical tool to solve the electrostatic differential problem,i.e.,introducing

    image charge outside the solved space,and making the total field formed by the image charge and the

    source charge satisfy the boundary. When this method is applied to the presence of adielectic,it will be found that

    the choice of image charge is not unique. This also accords with the uniqueness theorem of the electrostatic problem,

    because no matter what kind of image chargeis,the total field is the same. From the total field,the amount of

    bound charge can be obtained. At this time,it will be further found that the reisonly one kind of image charge equal

    to the amount of bound charge.

    Relationship between ground state energy and approximate level in parameter perturbation method
    WU Feng, MENG Li-juan
    College Physics. 2021, 40(2):  23-24.  doi:10.16854 /j.cnki.1000-0712.200121
    Abstract ( 676 )   PDF (947KB) ( 144 )  
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    Combining the parameter perturbation method with the wave functions that obeys space change symmetry, the ground state energy ( GSE) of the helium atom is calculated from the second to the twelfth level approximations. It is found that,with the increase of the level,the ground energy and its change decrease,and the absolute error between the calculated GSE and experiments exists small fluctuation. Therefore,the selection of approximate levels is vitally important for the accurate GSE calculation of the atom.
    An effective method of measuring the velocity of sound in metal rods with DIS
    YAN Qian, ZHU Fei-xia, YUAN Zheng-neng, WANG Kun-lin
    College Physics. 2021, 40(2):  25-31.  doi:10.16854 /j.cnki.1000-0712.200105
    Abstract ( 603 )   PDF (2085KB) ( 187 )  
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    An effective method of measuring the velocity of sound in metal rods is introduced by combining the standing wave method with acoustic sensors. A metal rod is fixed at its midpoint and vibration along its length is excited by rubbing it. A longitudinal standing wave is generated in the rod and sound waves are produced in the air. The digital information system ( DIS) is used to collect the sound signal and directly to display acoustic wave forms on the screen. The velocity of sound in the metal rod is then calculated and determined by measuring the fundamental frequency of sound waves in conjunction with the wavelength. The sound velocity in four different metal materials ( including aluminum,steel,brass,and copper) is measured respectively. The experimental results showed that the sound velocity obtained by this method is consistent in the same material metal rods of different lengths. The relative error of the sound velocity between the measured values and the well-known standard values in various metal materials is less than 6.00%. One advantage of this new method is that it can turn the acoustic signal into visible waveforms.

    Therefore,calculation parameters can be extracted directly and accurately from the waveforms.

    New discussion on data processing of Millikan oil-drop experiment
    ZHENG Xue-li, LI Qiao-mei, WANG Tao, HAN Zhong, LEI Di
    College Physics. 2021, 40(2):  32-35.  doi:10.16854 /j.cnki.1000-0712.200070
    Abstract ( 950 )   PDF (1345KB) ( 213 )  
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    The Millikan oil-drop experiment is one of the classic experiments in university physics,and the

    elementary charge can be calculated by experimental data processing. The experimental methods used by each university

    are basically identical,but the experimental data processing methods are various. The data processing combined

    with multiple methods is put forward to reduce the error caused by the data processing method,in which the

    data is pre-processed by grouping and processed by the least square method based on graphic method and the result

    shows that the error is significantly reduced. The ideas in this paper confirmed by five teaching classes are feasible

    and valid,which can be applied and promoted in actual teaching.

    Re-understanding the experiment of Millikan oil drop
    DONG Jian
    College Physics. 2021, 40(2):  36-41.  doi:10.16854 /j.cnki.1000-0712.200130
    Abstract ( 941 )   PDF (1493KB) ( 296 )  
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    The experiment of Millikan oil drop was considered to be appropriate for demonstrating the charge

    quantization,but the quantity of electric charge is not easy to be accurately measured by it,because there are many experimental difficulties need to be overcome. Many people expected to decorate the results with a late algorithm.The Brown motion of oil droplets was one of the important factors which had an impact on the balance voltage and the free fall time of the oil droplet. If reasonably dealing with it,the accuracy of the measurement could improve. Combining with the charge-numbering graph method,the charge quantization could be demonstrated concisely,and

    the more accurate value of Meta-charge could be obtained. The distribution characteristics of the charge measurement

    error is analyzed,and it is properly explained with the limit of the number of significant digits of the measurement data. It settles a theoretical foundation for selecting the suitable oil droplets.

    Experimental study of refractive index of edible oil based on spectrophotometer
    LI Xiao-kang, XU Shi-jun
    College Physics. 2021, 40(2):  42-47.  doi:10.16854 /j.cnki.1000-0712.200182
    Abstract ( 362 )   PDF (1527KB) ( 91 )  
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    In order to get the optical dispersion specificity of different edible oils,the change characteristics of

    its refractive index with the wavelength must be studied. After ignoring the scattering effect of light,a new doublelayer

    slide model for the spectrophotometer has been established,the slide is used to hold the rapeseed oil,sesame

    oil,kitchen waste oil,adulterated rapeseed oil,adulterated sesame oil,respectively,the transmission spectrum of

    380~1500 nm is obtained experimentally. Further,the change characteristics of the refractive index in the above

    five oil products with the wavelength are studied. The results have shown that the refractive index of five oil products

    is more similar with the change characteristics of wavelength,and the characteristic peaks of refractive index are all

    appeared at 1210 nm and 1400 nm wavelength; the refractive index of each oil product is significantly different at

    its characteristic peak,the refractive index of five oil products at the wavelength of 1210 nm is 1. 512,1. 472,

    1.456,1.576 and 1.612,respectively. This study has confirmed that the new double-layer slide model is feasible,

    the common refractive index characteristic value and the common characteristic spectrum have indicated that there

    are many related components in the different oil products. The refractive index characteristic value of five oil products

    at the wavelength of 1210 nm can be used as an effective index for the identification of oil products.

    Exploration and study of improving course teaching quality based on bottom line management
    LI Chen-xia, SHEN Wei-min, SHEN Chag-yu, KANG Juan, ZHANG Yan,   FEN Gui-lan, JIN Shang-zhong
    College Physics. 2021, 40(2):  48-51.  doi:10.16854 /j.cnki.1000-0712.200212
    Abstract ( 588 )   PDF (1439KB) ( 78 )  
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    Aiming at the problems of outdated teaching methods,lax process management,serious non-rigorous

    exam process,and difficulty of teaching quality control in traditional specialty courses,teachers of optical principles

    at China Jiliang University have explored and reformed the bottom-line management teaching.Through passing exams,

    basic training systems,formative evaluation reforms and other methods,students can truly meet the basic requirements

    of the curriculum,instead of allowing students to pass the curriculum assessment by reducing the difficulty

    of the test papers,narrowing the scope of the exams,and even disguised questions.Solving the problems that

    students,teachers and administrators are most concerned about in the course teaching at present.For students,they

    can solve the basic problems in the course learning in a timely manner without significantly increasing the burden,

    fully understand the basic methods and efforts of the course assessment,and clear ways to improve their ability and

    obtain help from teachers.Practice has shown that teaching reform based on bottom-line management has achieved

    good results in improving student learning efficiency,reducing teachers'repetitive work,and improving the quality of

    curriculum teaching.

    Sharing online teaching cases of college physics course
    WANG Li, CUI Jin-yu
    College Physics. 2021, 40(2):  52-54.  doi:10.16854 /j.cnki.1000-0712.200264
    Abstract ( 809 )   PDF (1962KB) ( 179 )  
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    The setting of college physics course in Yingkou Institute of Technology is introduced in this paper.

    The online teaching cases of college physics course in our university are shared from three aspects: preparation of

    online teaching resources,design of online teaching activities and methods of course assessment.The online teaching

    during the pandemic has opened a new door for the teaching reform of college physics course in our university.This

    teaching attempt will be continuously improved in the future teaching practice.

    A method to improve the online teaching quality of college physics during the pandemic period
    ZHANG Zi-jing, LIU Li-ping, ZHAO Yuan
    College Physics. 2021, 40(2):  55-58.  doi:10.16854 /j.cnki.1000-0712.200281
    Abstract ( 528 )   PDF (1269KB) ( 112 )  
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     For the demand of online teaching during the pandemic period,a new online teaching method based

    on real-time feedback of question choice is proposed by considering the characteristics of large class teaching of college

    physics courses and combined with the application experience of online MOOC courses and students' learning

    habits.In this paper the problems faced in the online large-class teaching of college physics courses are analyzes

    first,then the implementation plan of this method is comprehensively described through the designs of question

    time,question type,assessment methods of choice question.Finally,through one semester's teaching practice,the statistical

    results have showed that this method should effectively improve the quality of online teaching.

    Generalized thermal wavelength: definition,significance and applications
    LI Xin-yu, ZHANG Zi-yi, WANG Xin, LIU Quan-hui
    College Physics. 2021, 40(2):  59-62.  doi:10.16854 /j.cnki.1000-0712.200139
    Abstract ( 1092 )   PDF (1125KB) ( 168 )  
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    Photon gas and highly degenerate quantum gases are not classical ideal gas at all,and each of them has its own mean momentum from which a generalized thermal wave length can be thus defined,and the usual thermal wave length is an irrelevant concept.For a non-degenerate system,this wave length converges to the usual thermal one form a matter particle.For a degenerate system,the dimension of thermodynamic system must be larger than this generalized thermal wavelength,which leads to a criterion on the minimum dimension of the thermodynamic system.For some typical systems,we use the criterion to give their minimum dimensions.

    Virtual simulation and hardware improvements of the laser Doppler velocimetry experiment
    MAO Meng-hui, SONG Zhe-xiang, LUO Tian-hai, CAI Wei,
    College Physics. 2021, 40(2):  63-69.  doi:10.16854 /j.cnki.1000-0712.200297
    Abstract ( 752 )   PDF (2445KB) ( 292 )  
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     Due to the limited sampling rate of hardware and the weak auto-processing performance in the traditional

    laser Doppler velocimetry experimental system,virtual simulation and hardware improvements of the system

    are carried out in this work.To develop the virtual simulation,Unity 3D and Matlab Apps are employed to model the

    experimental principles and the related signal processing methods.In this way,students could gain a deeper understanding

    of the experimental system. Meanwhile,for hardware improvements,a convenient high - speed data

    acquisition system is constructed by using LabVIEW programming and digital oscilloscope.And then the sampling rate of the existing hardware is increased from 50 MSa /s to 2 GSa /s.In the parts of software system,various digital

    processing modules,such as digital filtering and automatic measurement,are realized to highly improve the performance

    of the current experimental system.This work provides a reference for the teaching content and system design of

    laser Doppler velocimetry.

    A brief illustration on some problems in one-dimensional  quantum scattering
    YING Wen-xiang, PENG Kai-yue, CAO Long
    College Physics. 2021, 40(2):  70-74.  doi:10.16854 /j.cnki.1000-0712.200086
    Abstract ( 628 )   PDF (1305KB) ( 266 )  
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    We give a simple discussion on the methodology of one-dimensional quantum scattering problems.

    Some problems and misunderstandings in one-dimensional quantum scattering are explained and clarified.

    Visualization analysis of infinite potential wells
    XIAO Guang-yan, CHEN Feng-xiang, WANG Li-sheng
    College Physics. 2021, 40(2):  75-79.  doi:10.16854 /j.cnki.1000-0712.200289
    Abstract ( 778 )   PDF (2895KB) ( 306 )  
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    With a computation software,many common in finite potential wells are visualized,and a corresponding

    GUI interface is designed to select different potential wells.After a potential well is selected and the corresponding potential

    well parameters and quantum numbers are set,the wave function,probability density function of low dimensionalgrangian function of any system with finite degrees of freedom and the constraints are provided,the approximate solution

    can be found. And this simple method can be applied to the approximate calculation of the bicycle system to

    analyze the motion and stability of the bicycle.

    Computer simulation of bicycle system
    JIANG Xing-yu
    College Physics. 2021, 40(2):  80.  doi:10.16854 /j.cnki.1000-0712.200146
    Abstract ( 668 )   PDF (1713KB) ( 134 )  
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    A bicycle system is a complicated one with non-complete constraints,which can be solved by the

    Euler-Lagrange equation according to least action principle. The approximate calculation is solved by using the

    difference instead of the differential and methods to correct the truncation error. Using MATLAB,as long as Lagrangian function of any system with finite degrees of freedom and the constraints are provided,the approximate solution

    can be found. And this simple method can be applied to the approximate calculation of the bicycle system to

    analyze the motion and stability of the bicycle.