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    20 February 2020 Volume 39 Issue 02
      
    The partyfor Cosmology is over?—Comments on Nobel Prize in physics in 2019
    ZHANG Tong-jie, WEI Xing
    College Physics. 2020, 39(02):  1-4.  doi:10.16854 / j.cnki.1000-0712.190589
    Abstract ( 1002 )   PDF (733KB) ( 556 )  
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    In 2019，the Nobel Prize in physics was awarded to Professor James Peebles of Princeton University，

    Professor Michel mayor of Geneva University，Switzerland，and Didier Queloz of University of Geneva，Switzerlandand professor of Cambridge University，UK for their research on understanding the evolution of the universe and the

    position of the earth in the universe made a great contribution. Based on this，this paper reviews the important con

    tributions of the Nobel Prize in physics to cosmology and exoplanets，the new features of this year’s Nobel Prize.

    Heisenberg's matrix mechanics
    HUANG Yong-yi, SHAO Guo-yun, ZHANG Chun-min
    College Physics. 2020, 39(02):  5-9.  doi:10.16854 / j.cnki.1000-0712.190178
    Abstract ( 1673 )   PDF (220KB) ( 617 )  
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    The paper recalls the theoretical frame of matrix mechanics，including the fundamental commutation

    relation，Heisenberg motion equation of operators and nondegenerated perturbation theory. The matrix mechanical

    treatment of onedimensional harmonic oscillator is also given.

    Weak-field approximation of Brans-Dicke's theory of gravitation
    ZHENG Fu-you, YANG Jin-song
    College Physics. 2020, 39(02):  10-14.  doi:10.16854 / j.cnki.1000-0712.190355
    Abstract ( 1388 )   PDF (197KB) ( 481 )  
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    As one of the most important modified theories of gravity，Brans-Dickes theory of gravitation plays

    an important role in studying the motions of stars and cosmic evolution，as well as in explaining cosmic phenomena.

    There is no doubt that solutions to Brans-Dickes field equations are of great significance in this theory. However，it

    is very difficult to obtain exact solutions to the Brans-Dickes field equations in general cases because of the non

    linearity of these equations，although some special solutions can be obtained in some cases. Fortunately，in these

    cases that the gravitational field is weak and the source of the gravitational field moves slowly，one can easily find

    approximate solutions to these field equations. In this paper，we aim at the weakfield approximate solutions to

    Brans-Dickes field equations. Firstly，based on the weak gravitational field，we expand the Brans-Dickes scalar

    field and spacetime metric in the corresponding background fields. Then，we substitute the scalar field and spacetime

    metric into Brans-Dickes field equations to get these corresponding linearized field equations，and we further

    simplify one of them using a specific gauge condition. Finally，we solve the linearized field equations under the

    slow-motion condition，and obtain the weak-field，slow-motion approximate solutions to Brans-Dicke's field equations. These approximation solutions obtained in this paper can provide useful reference for the teaching and research in Brans-Dicke's theory of gravitation.

    Discussion on the upper limit of electrostatic shielding
    CEN Xian-zhuo, DENG Wei-tian
    College Physics. 2020, 39(02):  15-17.  doi:10.16854 / j.cnki.1000-0712.190077
    Abstract ( 2242 )   PDF (337KB) ( 598 )  
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    The conductor shell in external electric field will produce inductive charge on its outer surface，and

    reach the electrostatic balance. The electric field in its cavity is zero everywhere，this is so called electrostatic shielding. However，if the external electric field is extremely strong，or the number of free electrons in the conductor is

    too small，so that the inductive field cannot offset the external field completely. This is so called the upper limit of

    electrostatic shielding. In this paper，we simplify this problem as a toy model in which the conductor shell，is illustrated as a pair of parallel metal plates. Through calculation quantitatively，we have found that due to the large amount of free electrons in the metal，any macroscopic conductor devices are far from encountering this upper limit

    in non-extreme question.

    The energy loss of viscous flow in a horizontal circular pipe
    ZHOU Yue, ZHANG Guo-feng
    College Physics. 2020, 39(02):  18-20.  doi:10.16854 / j.cnki.1000-0712.190192
    Abstract ( 1135 )   PDF (224KB) ( 442 )  
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    The origin and distribution of the energy loss and heat in a laminar flow of viscous fluid through a

    horizontal circular pipe are analyzed，and a misconception about the energy loss term in Bernoulli’s equation of vis

    cous fluids was corrected.

    Study on the electrical properties of an arbitrary n-order polygonal resistor network
    HUANG Jian-lan, 　TAN　Zhi-zhong
    College Physics. 2020, 39(02):  21-25.  doi:10.16854 / j.cnki.1000-0712.190062
    Abstract ( 949 )   PDF (552KB) ( 474 )  
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    This paper uses Kirchhoff’s law to study the electrical properties (node voltage，branch current，

    equivalent resistance)of an arbitrary n-order polygonal resistor network by establishing a differential equation model. Firstly，the differential equation model is established by using the Kirchhoff current law，and the general and special solutions of the difference equation are also studied，then the voltage formula of each node is obtained.Based on the voltage results，the formulae of branch current and equivalent resistance are derived. The research in this paper is of great theoretical value and practical significance in promoting physical inquiry teaching and cultivating students’ability of scientific inquiry.

    Application of TracePro in polarization experiment of light
    ZHONG Ke-jun, FU Yan-jun, ZHU Quan-shui
    College Physics. 2020, 39(02):  26-30.  doi:10.16854 / j.cnki.1000-0712.190107
    Abstract ( 2006 )   PDF (2238KB) ( 990 )  
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    In order to improve the teaching effect and teaching quality of polarization experiment of light，a professional optical design software，TracePro，is introduced into the teaching to simulate the light.The process and phenomenon of birefringence and the principle of polarizer are established，and the physical model of polarization experiment system of light is established.The parameters and conditions of each component are set up according to the requirements to complete the “whether to save or not”.In the experiment of judging the polarization state of light，the polarization state conversion phenomenon of light passing through the wave plate is simulated，and Marius’law is verified，the optical separation of dielectric film and optical rotation are simulated also.The results show that this method can improve teaching efficiency，stimulating students to explore the subjective initiative of science，and the simulation results are consistent with the theoretical and experimental results.

    Temperature sensing experiment of intensity demodulated fiber Bragg grating
    ZENG Fan-chao, GAO Hong-yun, HU Qi, LI Min
    College Physics. 2020, 39(02):  31-33.  doi:10.16854 / j.cnki.1000-0712.190138
    Abstract ( 985 )   PDF (304KB) ( 382 )  
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    Fiber Bragg grating has been widely used in engineering fields.Because of the complex demodulation system，high cost，and the need to use fiber Bragg grating wavelength interrogating system，fiber Bragg grating is difficult to demonstrate in the experiment teaching of undergraduate courses.In this paper，an intensity demodulation method based on a narrow line-width DFB laser is proposed，which can greatly simplify the demodulation system of fiber Bragg grating sensor and fully meet high resolution and real-time detection system requirements.Properly arranged temperature sensing experiments could intuitively show the linear sensing performance of fiber gratings.The engineering fiber Bragg grating sensing technology could easily demonstrate in undergraduate education. Students should better understand and master the optical fiber sensing technology in engineering application through the experiment.The intensity demodulation system is of great value to promotion and application.

    Introducing extraordinary optical transmission into demonstration experiment in class
    PEI Yan-bo, YAO Feng-feng, ZHANG Yu, ZHAO Yuan
    College Physics. 2020, 39(02):  34-38.  doi:10.16854 / j.cnki.1000-0712.190157
    Abstract ( 1135 )   PDF (960KB) ( 530 )  
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    This paper discusses how to introduce extraordinary optical transmission，which is one of frontiers of optical research，into single slit diffraction experiment demonstrated for University Physics class. Based on numerical simulation，the diffraction phenomenon of nano scale singleslit and micro scale single-slit are compared under Fraunhofer diffraction condition. It is pointed out that such anomalous diffraction charateristics of nano scale single slit originates from the strong interaction between light and matter in nanoscale，which is not significant in the Fraunhofer diffraction from micro scale single slit. Finally，the design of the demonstration experimental system for class is discussed.

    Research on the suppression method of laser speckles in the experiment of measuring the refractive index of plane glasses
    WANG Jing, YANG Yan-dan, LI Chao-rong
    College Physics. 2020, 39(02):  39-42.  doi:10.16854 / j.cnki.1000-0712.180684
    Abstract ( 903 )   PDF (1383KB) ( 283 )  
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    In this paper，the appearance of laser speckles in the experiment of measuring the refractive index

    of plane glasses using laser as the optical source is described. A simple and effective suppression method of the laser

    speckles is obtained. By using statistical rules，the factors influencing the contract of speckles are summarized from

    analyzing the micro-beam interference field caused by laser diffusers. A staticrotated diffuser couple is chosen as

    the reducer in the experiment，in which a static diffuser are added to increase the roughness of the incident laser

    beam，and then the contrast of the speckles can be reduced to around 4% by using a rotating diffuser with a very

    slow speed. As a result，very clear interference fringes can be observed at this situation.

    Research on pro detection of dark matter based on DAMPE
    ZHENG Ying, WANG Run-na, LI Xin, ZHU Feng-rong, HE Yu, CHEN Qi-hui
    College Physics. 2020, 39(02):  43.  doi:10.16854 / j.cnki.1000-0712.190118
    Abstract ( 1087 )   PDF (319KB) ( 349 )  
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    In the 1930s，astronomical observations presented severe challenges to the standard universe model.

    In order to reconcile the contradiction between observational data and theoretical models，theoretical physicists proposed dark matter theory. Since then，experimental physicists have explored various dark matter detection schemes.

    This paper introduces the origin of dark matter concept，the basic properties of dark matter，the principle and method of dark matter detection and the latest progress of DAMPE in detecting dark matter. The focus is on DAMPE data，with electronic spectrum analysis as the core，before based on human research，the multilevel and multidirectional synthesis of DAMPE data and results further elaborates the profound significance of Tev inflection and sharp signal in DAMPE electronic spectrum. Finally，relying on some information obtained during the research process，put forward some opinions and insights on future dark matter detection experiments.

    How to find the centrifugal force by Christian Huygens
    SHEN Xian-yong
    College Physics. 2020, 39(02):  47-50.  doi:10.16854 /j.cnki.1000-0712.190213
    Abstract ( 3157 )   PDF (922KB) ( 540 )  
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     The centrifugal force was first displayed in the appendix of“Horologium Oscillatorium”published in

    1673 by Christian Huygens，and Huygens just wrote down the calculation of the centrifugal force without further explanation.

    However， the derivation from Huygens was published firstly in 1703 when Huygens was dead.And the derivation

    will be viewed in this paper.

    The influence of the new reform of college entrance examination on the physics learning attitude of Zhejiang students
    GE Di, ZHANG Rui, QI Yue-ying, WANG Zu-yuan
    College Physics. 2020, 39(02):  51-55. 
    Abstract ( 946 )   PDF (922KB) ( 503 )  
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    In this paper，Colorado Learning Attitudes about Science Survey ( CLASS) is used to evaluate students' physics learning attitude. It is found that the new reform of college entrance examination has a great influence on the physics learning attitude of Zhejiang students. There are significant differences in the attitudes of the two groups of students in Xue Kao and Xuan Kao. The " college physics AP" course has made some effects on amending these differences. With the college physics AP，the achievements in physics of the students in Xue Kao are improved，and the training of the physics thinking for the students is strengthened，which has offset the influence of the new reform of college entrance examination to some extent.

    Dynamics analysis of Heron's fountain
    PENG Liang-tao, CHEN Ting, YAO Zhen-yu
    College Physics. 2020, 39(02):  56-61.  doi:10.16854 /j.cnki.1000-0712.190123
    Abstract ( 1936 )   PDF (708KB) ( 945 )  
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    In this paper，a Heron's fountain is constructed. The modified unsteady Bernoulli equation and the

    continuity equation are used to solve the dynamic equation under the laminar and unsteady basic assumptions. A

    mathematic software is used to combine the experimental parameters with the numerical solutions. The relationship

    between the height of the jet and the time is deduced theoretically. Its relationship with the height of the bottle on

    　　the right side，the cross-sectional area，the height of the fountain outlet，and the diameter of the pipe is also discussed.

    　　At the same time，tracker software is used to track the maximum jet height of the fountain，and the model of

    　　the air spring is established to complete the mutual verification of theory and experiment.

    A method for measuring linear expansion coefficient of metal 　　based on Fabry-Perot etalon
    DAI Cong-ling, RONG Zhen-yu, YANG Yi-fan, JIANG Yi-mai, HAN Yu-jing
    College Physics. 2020, 39(02):  62-65.  doi:10.16854 /j.cnki.1000-0712.190218
    Abstract ( 1124 )   PDF (623KB) ( 716 )  
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     In this paper，a method for measuring linear expansion coefficient of metal based on the Fabry-Perot

    ( F-P) etalon is proposed. The elongation of metal rod during thermal expansion can be converted into the

    change of interference fringe radius in interference optical field of F-P etalon via optical lever. The linear expansion

    coefficient of metals can be obtained by measuring the distance between interference fringes. It only needs to measure

    the distance between the outer fringes of the interference optical field by the F-P etalon，and the multi-beam equal

    inclination interference of the F-P etalon can produce sharp interference fringes，the measurement process is

    much simpler，and the accuracy of the measurement result is much higher. The experiment results have demonstrated

    the feasibility and reliability of the method.

    The Great Physicist in 20 Century—Niels Bohr
    CHEN Bo, HE Biao, LI You-zhen, XU Fu-xin
    College Physics. 2020, 39(02):  66-68.  doi:10.16854 /j.cnki.1000-0712.190110
    Abstract ( 2938 )   PDF (118KB) ( 616 )  
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    Niels Bohr ( 1885-1962) was a famous physicist in the 20 century. He published his three papers

    which later became famous as“the trilogy”in his early years. Four stories of Niels Bohr were introduced in this paper，

    which were his description of“Frank-Hertz”experiment，foundation of the Institute of Theoretical Physics of

    the University of Copenhagen，good-natured arguments with Einstein，and involvement with the establishment of

    　　the European Organization for Nuclear Research，known as CERN. These stories demonstrated his preeminent intelligence，

    　　respectable personality，profound patriotism and the spirit of his dedication to the human peace.

    Simulation and visualization ofthe orbital motion of celestial body based on VPython
    WU Yong-hao, LIU Yu-ying, SONG Min
    College Physics. 2020, 39(02):  69-73.  doi:10.16854 /j.cnki.1000-0712.190068
    Abstract ( 2642 )   PDF (530KB) ( 1506 )  
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     The concepts of motion，force，momentum，energy of objects are basic and very important in the

    teaching of College Physics. In Newton mechanics，the future motion state can be predicted for an orderly system if

    the initial condition is given. Newton mechanics makes a great success in astronomy. In this paper，by using universal

    law of gravity，the theorem of momentum and combining the VPython software，the motion of the celestial body

    　　is studied. The special examples discussed in detail are the satellite and the moon orbiting with the earth，the Mars

    　　rotating about the sun，and the satellite moving around the binary star，etc. The path and the moving process could

    　　be visualized intuitively in real time. The teaching experience indicated that simulating and visualizing the orbital

    　　motion of celestial body based on VPython is a very powerful method to improve student's ability of understanding

    　　and applying Newton's law of motion and theorem of momentum.

    The topological description of Ampère s circuital law
    TANG Jian-li, LI Yi-wen, ZHU Jun-an, LIANG Qi-feng
    College Physics. 2020, 39(02):  74-77.  doi:10.16854 /j.cnki.1000-0712.190056
    Abstract ( 1388 )   PDF (371KB) ( 518 )  
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    Topology has been widely discussed in quantum mechanics in recent years. In this paper，the integral

    formula of Ampère s circuital law is re-expressed as the integral formula of the first Chern number of a vector

    field defined on the torus parametric surface. The numerical simulation shows that the integral value is an integer，i.

    e.，the first Chen number，which represents the global property of vector field: When the vector field undergoes

    continuous transformation，the local value of the vector field changes，however the integral value，i.e.，the Chern

    number，remains unchanged; if the Chern number changes，it implies the vector field has experienced a discontinuous

    change and there rises the singularity in the distribution of vector field. Furthermore，the vector field is

    mapped from torus parametric surface to the unit sphere by Gauss mapping，and the intuitive geometric meaning of

    the first Chern number is given. The theoretical and numerical results reveal the topological nature of Ampère s circuital

    law，and show that the concept of topology can also be widely applied in classical physics.

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