Table of Content

20 April 2020 Volume 39 Issue 04

  

Interference of diffraction by a double grating

XIAO Guo-hong, ZHONG Xi-hua, ZHANG Qian

College Physics. 2020, 39(04):  1-4.  doi:10.16854 / j.cnki.1000-0712.190341

Abstract ( 1935 )   PDF (948KB) ( 1270 )  

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The effect of interference of diffraction by a double grating is worthy to study theoretically and provides possibilities of application. We calculate the pattern of Fraunhofer diffraction by a cosine-style double grating with a wavefront phase-factors method. Some formulas about intensities of each order diffraction are deduced as one grating translates along another. Some experiment results are shown to coincide with the diffraction patterns by numerical simulation. These formulas form a foundation for experimental applications. One of these obvious applications is to measure the amplitude and the frequency of a micro-vibration.

Strict mathematical theory of normal boundary valuerelationship of electromagnetic field

LUO Ling-xiao

College Physics. 2020, 39(04):  5-9.  doi:10.16854 / j.cnki.1000-0712.190388

Abstract ( 1286 )   PDF (344KB) ( 570 )  

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Expounded though the flux which vector field through the second order infinitesimal plane is also the second order dimensionless，but in particular cases demand the computational accuracy must achieve the third order dimensionless. For this purpose，it needs to divide the second order infinitesimal plane into infinitely many fourth order infinitesimal surface element to calculate the flux，and give the law that followed by the result that obtained through such calculation：The theorem of vector field through second order infinitesimal plane under third order infinitesimal accuracy. It also introduces this theorems application in the divergence theory and in the theory of electromagnetic field normal boundary value relations.

How much work does it take to stop the Earth rotating?——Talking about “wandering Earth”

YU Feng-jun, JIA Shuan-wen, TIAN Jun-long, TANG Zhen-jie

College Physics. 2020, 39(04):  10-12.  doi:10.16854 / j.cnki.1000-0712.190191

Abstract ( 1625 )   PDF (208KB) ( 1007 )  

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Starting from a grand plan of a domestic sci-fi blockbuster “The Wandering Earth”，the minimum mechanical work needed to stop the Earth rotating is deduced and calculated by using the law of conservation of momentum moment，the theorem of kinetic energy and the concept of the first cosmic velocity. The result is about 4.1×1030 J.The problem of feasibility of stopping the Earth rotating is discussed from the viewpoint of energy.

Dimensional solution and consideration of three-line pendulum

SHI Wei-gang, YAN Tian-tian

College Physics. 2020, 39(04):  13-15.  doi:10.16854 / j.cnki.1000-0712.190232

Abstract ( 1125 )   PDF (240KB) ( 528 )  

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Dimensional analysis is a very important content in college physics teaching，but there are still some big deviations in the process of teaching at present. For this reason，taking the dimensional analysis method of rotational inertia of three-line pendulum as an example，this paper compares the results of general dimension solution with the revised after considering the action form of physical quantities，and expounds the contents that should be considered in the process of applying dimension solution.

Rotational inertia of a Mobius ring body

QIU Wei-gang

College Physics. 2020, 39(04):  16-17.  doi:10.16854 / j.cnki.1000-0712.190257

Abstract ( 1494 )   PDF (188KB) ( 727 )  

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The center of a regular triangle translates along a circle while rotate along the axis perpendicular to the triangle plane and through the center. If the rotation angle is an integer multiple of 120 degree，the rotated triangle coincides with the original one just after a round circle. This twisted rigid body is called Mobius ring body and its rectangular coordinates are given in the parameters form. Its rotational inertias are calculated just from the integration definition.

A method for judging the properties and the chiral characteristics of photonic crystals

LI Yan

College Physics. 2020, 39(04):  18-22.  doi:10.16854 / j.cnki.1000-0712.190235

Abstract ( 1346 )   PDF (902KB) ( 387 )  

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By studying the angle relationship between the wave vector and the Poynting vector of the electro-magnetic field in isotropic or anisotropic media，the method for determining the dielectric properties and chiral characteristics of photonic crystals by using the dot product between the unit wave vector and the unit group velocity of

　　the electromagnetic field has been given. It is pointed out that the criterion for the critical value of the chiral charac

　　teristic of photonic crystals can be used to solve the problem of multi-beam combination. At last，the above conclu

　　sions are discussed by analytic calculation. The above results have laid a foundation for further enriching the con

　　tents of electrodynamics and other related course.

Discussion on the paper “Analytical solutions of the Madelung constant of double atomic chain on circles”

ZHOU Qun-yi, MO Yun-fei, HOU Zhao-yang, LIU Rang-su

College Physics. 2020, 39(04):  23-27.  doi:10.16854 / j.cnki.1000-0712.190195

Abstract ( 1624 )   PDF (850KB) ( 645 )  

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The Madelung constants of atomic chain is calculated by accumulation method，Evjen method and mean value method，and the results are compared. It is found that the Madelung constants of atomic chain with finite length is different from that of circles. It is also found that the Evjen method is equivalent to the mean value method by means of plotting graph. Two errors in the paper “Analytical solutions of madelung constant of double atomic chain on circles”are revised，and it is proposed to revise the definition of dimerization Madelung constant，so that its physical concept is more obvious.

Study on the drainage time and the flow coefficient in the experiment of the flow velocity of small holes

HUANG Yu-hong, ZHANG Suo-bin, WEI Fen-fen, ZHANG Zong-quan, HOU Yun-bo

College Physics. 2020, 39(04):  28-33.  doi:10.16854 / j.cnki.1000-0712.190271

Abstract ( 2670 )   PDF (688KB) ( 1228 )  

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The tank drainage problems in the experiment measuring the flow velocity of small holes are systematically，theoretically and experimentally studied by taking water as the ideal fluid and considering head loss and or ifice contraction effect. The analytical solution of the cylindrical tank drainage time is theoretically obtained for the first time. Furthermore，the variation of drainage time with free surface velocity and flow coefficient is discussed.Based on this，the equivalent interval of drainage time is proposed. In the experiment，large cylindrical tanks with different sized exit orifice locating at the bottom are designed and fabricated. The tank drainage time varying with the height of liquid surface is measured. The flow coefficient is calculated from the experimental data and the proposal of equivalent time interval is further validated. The experimental results are in good agreement with theoretical calculations.

A short-cut analysis of the first order RC response under square wave excitation

ZHAO Qiang, SUN Dian-ping, ZHANG Wen-qian, GUO Chao-xiu

College Physics. 2020, 39(04):  34-36.  doi:10.16854 / j.cnki.1000-0712.190222

Abstract ( 2418 )   PDF (267KB) ( 710 )  

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When a square wave voltage u with the period T，the amplitude Um and the duty ratio δ is used as the excitation，it is deduced explicitly by a simple method that the values of the response，uc，the voltage across the capacitor，on the rising edge and falling edge will converge monotonically and continuously to Um(1-A1 )A2 / (1-A1 A2)and Um(1-A1 )/ (1-A1 A2 )，respectively (where A1 = e-Tδ / (RC)，A2 = e-T(1-δ)/ (RC)).Moreover，the relationships among the parameters are also discussed. The results are not only useful for understanding and analyzing the experimental phenomena of the first-order RC transient process under square wave excitation，but also helpful for improving the experimental design.

Analysis of grating diffraction by photoelectric detection technique

LANG Xian-zhong, WU Qin, MA Ji, TANG Bin, SU Jiang-bin, JIANG Mei-ping

College Physics. 2020, 39(04):  37-41.  doi:10.16854 / j.cnki.1000-0712.190265

Abstract ( 1290 )   PDF (1363KB) ( 730 )  

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Diffraction characteristics of polycarbonate (PC)layers of recordable optical discs are investigated

by photoelectric detection technique. The results such as diffraction spectrum range，distribution of diffracted light intensity，spectral overlap，free spectral range，relationship between angles and wavelength，angular resolution and grating constant are analyzed，respectively. The experimental results are consistent with the diffraction theory. The method makes up the shortage of traditional grating experiments and it is helpful to improve undergraduates' recognitions on diffraction grating in the college optics.

Achievements and perspectives of  Mössbauer spectroscopy in solid state research

XU Ke, MA Ke-yan, WANG Hai-jun

College Physics. 2020, 39(04):  42-47.  doi:10.16854 / j.cnki.1000-0712.180576

Abstract ( 1355 )   PDF (1850KB) ( 1171 )  

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More than 50 years ago，in his doctoral thesis，the young German physicist Rudolf Ludwig Mössbauer proposed the Mössbauer effect，which developed into Mössbauer spectroscopy. His discovery of the recoilless resonance effect of gamma rays emitted and absorbed energy was awarded the Nobel Prize in physics in 1961. His discovery led to the development of a new test technique for the ultrafine interaction between nuclear moments and electromagnetic fields. This method，with an accuracy of 1013 orders of magnitude，can be used to anayze the valence，symmetry，magnetic behavior，phase transitions，lattice vibrations，and many other solid properties of matter.

Design and application of the mobile learning platform of college physics based on Android

TONG Yu-xuan, TIAN Ze-an, DENG Hui-qiu

College Physics. 2020, 39(04):  48-52 .  doi:10.16854 / j.cnki.1000-0712.190255

Abstract ( 1231 )   PDF (1177KB) ( 679 )  

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As a new learning mode，mobile learning makes learners free from the constraints of time and space

and made the autonomous learning realized in the true sense. Based on the analysis of the current situation of college physics teaching and the needs of students ′learning，a collegebased physical mobile learning platform based on Android system is designed and developed in this paper，and is also appled to the curriculum to carry out in the teaching practice. Application effect of this platform is evaluated through tests and questionnaires.

Density of states of a free particle in infinite potential well

College Physics. 2020, 39(04):  53-55. 

Abstract ( 2408 )   PDF (144KB) ( 1483 )  

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For a free particle in finite container，in some thermodynamic statistics textbooks，the density of energy states is deduced based on momentum discrete values due to de Broglie relations and standing wave conditions from semi-classical quantum images. However，according to quantum theory，the particle in infinite potential well has energy eigenstates rather than momentum eigenstates. In this paper，we derive the state density of free particles in finite volume based on its energy eigenstates，and the results are in agreement with textbook. But our treatment seems to be more nature.

Acoustic resonator experiments based on LabVIEW

RONG Pan-xin, SONG Jun-hao, KANG Xiu-ying

College Physics. 2020, 39(04):  56-59.  doi:10.16854 / j.cnki.1000-0712.190263

Abstract ( 1610 )   PDF (608KB) ( 716 )  

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In order to measure the resonant frequencies of the acoustic resonance tube more efficiently，a frequency sweep program based on LabVIEW is designed. The resonant frequencies of different tube lengths with the front-end and tail-end closed are obtained respectively. In addition，the hypothesis is also validated that the acoustic antinode deviated by drawing the standing wave pattern in the tube. Finally，the influence of the opening and closing of the holes on the resonant frequency is investigated. It is found that the closer the holes to the antinode of the standing wave，the greater the deviation of the resonant frequency.

The dynamic method in Millikan oil-drop experiment

CHEN Shang-ming, LI Liang-feng, PAN Qi

College Physics. 2020, 39(04):  60-66.  doi:10.16854 / j.cnki.1000-0712.190290

Abstract ( 11448 )   PDF (914KB) ( 5412 )  

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In this paper the dynamic method of measuring the electric charge quantity of oil droplets is explored. Through the analysis of the dynamic process model，equations of the dynamic method for solving the charge quantity of oil droplets are obtained. A program of data processing for measuring the micro-electric charges by dynamic method is designed，which makes the dynamic method applied more easily in teaching. In addition，the analysis enriches the physical connotation of Millikan oil-drop experiment and deeps the understanding of the theoretical knowledge. The exploration results have an important and significant reference to the in-depth understanding of the process of oil-droplet electric charge measurement by the dynamic method.

The practice and discussion on the physical experiments with visualized programs designed by students themselves

TANG An-ke, WANG Lin, LIN Wei-hua

College Physics. 2020, 39(04):  67-72. 

Abstract ( 1387 )   PDF (1425KB) ( 651 )  

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The structural design of Tesla valves based on finite element analytical simulation and 3D printing technology

ZHANG Zhi-he, CHEN Zhen , CHEN Ting

College Physics. 2020, 39(04):  73-77.  doi:10.16854 / j.cnki.1000- 0712.190242

Abstract ( 2815 )   PDF (1485KB) ( 1191 )  

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Tesla valve is a passive oneway valve with fixed geometry structure. In recent years，it has gained wide attention and application in the field of microfluid. In this paper the working principle and basic configuration

of the Tesla valves are introduced. Some key parameters which affected the working performance of the Tesla valvesvare analyzed and the split angle is discussed as the main research object. The COMSOL multi-physics simulationvsoftware is used to simulate the internal fluid motion behavior of the Tesla valves. Tesla valves are fabricated by using 3D printing technology，and experiments are designed to verify the correctness of the simulation results. The　relationship between the liquid flow rate，the split angle and the pressure drop ratio are analyzed in details，and the best performance of the Tesla valves is obtained at a split angle of 10o.