College Physics

Polarization effect in electron-positron scattering and electron-electron scattering

LIN Qiong-gui

College Physics. 2017, 36(7): 1-4. doi:10.16854 /j.cnki.1000-0712.2017.07.001

Abstract ( 1361 )

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The 16 polarized cross sections for electron-positron scattering are calculated. They can be grouped into three classes according to the behavior of the angular distribution. The three classes have singularities sin-4( θ /2) ，sin-2 ( θ /2 ) and 1 in the forward direction， respectively. The 16 polarized cross sections for electron-electron scattering are also calculated. They can be grouped into three classes according to their singular behavior in either the forward direction or the backward direction. The singularities are similar to those for electron-positron scattering. A simple physical explanation is presented for the singular behavior.

The Goos-Hnchen shift of probability wave

SANG Zhi-fang，ZHANG Kai，GAO Lei

College Physics. 2017, 36(7): 5-8. doi:10.16854 /j.cnki.1000-0712.2017.07.002

Abstract ( 1577 )

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Many transmission properties of probability wave satisfying the Schrdinger equation are similar electromagnetic wave. The exit point of electromagnetic wave totally reflected by interface separating two deferent refractive index media experiences the Goos-Hnchen shift corresponding to the incident point. The Goos-Hnchen shift also takes place in the probability wave. In this paper，the expression of the Goos -Hnchen shift in the probability wave is deduced when it pierces through the rectangular potential barrier，and the relationships with incident angle. The width of potential barrier and electronic energy are also discussed.

Calculation of exciton energy level in two-dimensional transition metal dichalcogenides———Dielectric screened hydrogen model

JIA Guang-yi，HUANG Zhen-xian，ZHAO Guo-zhen，MA Qiao-yun

College Physics. 2017, 36(7): 9-11. doi:10.16854 /j.cnki.1000-0712.2017.07.003

Abstract ( 1621 )

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Binding energy and energy level of an exciton in monolayer MoS2 are calculated by using the dielectric screened hydrogen model. By comparing with the results calculated via Bohr hydrogen model in two -dimensional space，it is found that the dielectric screening gives rise to a larger binding energy in exciton excited states and smaller level spacing between excited states and ground state. As a result，only when the principal quantum number is larger than 8，the quantization disappears and the exciton show a continuous energy level spectrum.

College of Physics and Electrical Engineering，Anyang Normal University，Anyang，Henan 455000，China

YU Feng-jun

College Physics. 2017, 36(7): 12-13. doi:10.16854 /j.cnki.1000-0712.2017.07.004

Abstract ( 1224 )

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Starting from the fact that the speed of light in a vacuum is the largest and the law of refraction ( or ray trace equation) ，it is proved that the initial angle α of the light ray being able to return to the ground in mirage can not be arbitrary. When α is greater than the certain value αm，the light emitted from a point is not able to return to the ground. The other factors affecting αm are also given.

A vibration model for the linear triatomic molecule

CHEN Kui-fu，MIN Shun-geng

College Physics. 2017, 36(7): 14-18. doi:10.16854 /j.cnki.1000-0712.2017.07.005

Abstract ( 1718 )

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A classic mechanics model is presented to account for the vibration of a linear triatomic molecule. In this model，a coil spring loops two chemical bonds. The coil spring possesses the potential energy in the bending mode，rather than the longitudinal spring along the bonds. The ordinary differential equation system of this model is formulated. By solving equation system，three eigenvibration frequencies and the corresponding modes are obtained.This model is validated by the literature data of three molecules，carbon dioxide，carbonyl sulfide and hydrogen cyanide. The results indicate that three eigenfrequencies of the presented model fit the literature data well.

An analytic solution of the locus of tracking problem

LI Li，ZHANG Yin

College Physics. 2017, 36(7): 19-20.

Abstract ( 808 )

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For tracking problem，general literatures just compute the time of catching up with object or under the known position，where tracker catches up and the ratio of velocity between them is calculated. Obviously，it is more important to obtain analytic solution. This paper obtains the general expression about the question by establishing and solving 2nd-order ODE. It deduces the same conclusions with other literatures under the known onditions at last.

The visual image of a moving object in special relativity

LIU Jia-ming， JIANG Jun-qin

College Physics. 2017, 36(7): 21-24. doi:10.16854 /j.cnki.1000-0712.2017.07.007

Abstract ( 1387 )

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We propose a more exact model for the study of the visual image of the moving object by considering

a pinhole imaging process on the base of the point observed model. We derive the exact theory formulas for the

calculations. Considering the cube for instance，we show the visual images of it with low and high speeds on one

observed direction. The edge of cube with high speed will be bent in the visual image. The difference between the

cases of closing to observer and away from the observer is discussed.

Capacitance of symmetric elliptic cylindrical capacitor

WANG Qiu-yu，CHEN Gang，LIN Xiao-ting

College Physics. 2017, 36(7): 25-27. doi:10.16854 /j.cnki.1000-0712.2017.07.008

Abstract ( 1107 )

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Elliptical plate capacitor made of slots in the elliptical cylindrical plate is a form of capacitor. In this　paper，the conformal mapping method is used to solve the capacitance value of the symmetric elliptic cylinder plate capacitor with different slit width.Using the method of Zhukovsky transformation，we convert a symmetric elliptic cylindrical capacitor to a symmetrical arc - cylindrical capacitor. The capacitance of slotted elliptic cylindrical capacitor with different slit width is found out in terms of the results of the symmetrical arc-cylindrical capacitor reference from the literature.

New method of measuring damping constant via damping vibration

HUANG Yu-hong，ZHANG Suo-bin，ZHOU Wen-fei，YANG Zong-li，ZHANG Zong-quan

College Physics. 2017, 36(7): 28-32. doi:10.16854 /j.cnki.1000-0712.2017.07.009

Abstract ( 1904 )

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The formula of maximum velocity attenuation is derived by using the damping vibration model of springs and slider on the air track，then the damping constant of the air track is deduced. Moreover，the damping constant is inferred from the perspective of quality factor and the method can be considered as an approximation of maximum velocity attenuation method if the damping is small enough. By two designed damping vibration experiments on the air track，the damping constants corresponding to above-mentioned different algorithm are obtained by using measured amplitude，cycle and light shielding time，et al. and the results agree well with each other. Furthermore，the video of moving slider is recorded by playing slowly the video，the attenuated vibration amplitudes and the corresponding damping constants are obtained by using the method of maximum amplitude attenuation. The results show will agreement with those values obtained from the methods of maximum velocity attenuation and quality factor. Therefore the proposed methods to measure the damping constant are proved to be reliable from another point of view. Such methods are practicable and easy to operate in experiment，also the results are tested to be reliable.These proposed methods have provided new ways of thinking to measure the damping constant.

Experimental scheme design of steady state characteristic of RC filter circuit

QIAN Jun，HUI Wang-wei，LIU Li-jun，ZHANG Zun-yue，ZHANG Chun-ling

College Physics. 2017, 36(7): 33-36. doi:10.16854 /j.cnki.1000-0712.2017.07.010

Abstract ( 1154 )

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Based on the experiment of the steady state characteristic of the traditional RC series circuit and combined with the relevant contents of electromagnetic theory courses，we propose the experimental scheme design of steady state characteristics including the second order RC filter circuit. The amplitude-frequency and phase-frequency characteristics of the first order and the second order RC filters are compared and analyzed. This experiment is very helpful to students to understand the principle of filtering，and to master the knowledge of the Kirchhoff equations in the AC circuit.

Discovery and early research on nuclear magnetic resonance by Edward

Mills Purcell

YIN Xiao-dong，WANG Xin-yan，LIU Zhan-cun

College Physics. 2017, 36(7): 37-44. doi:10.16854 /j.cnki.1000-0712.2017.07.011

Abstract ( 1120 )

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The biography of Edward Mills Purcell is sketched. His discovery for the nuclear magnetic

resonance in condensed material and the innovation experiences of early research of NMR are reviewed. How he

seized opportunity，and was good at learning，applied reverse thinking mode ingeniously and made bold attempt is

analyzed.

The establishment，operation and enlightenment of the research team of theoretical physics in University of Michigan

YANG Qing-yu

College Physics. 2017, 36(7): 45-50. doi:10.16854 /j.cnki.1000-0712.2017.07.012

Abstract ( 1348 )

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The latter part of the 1920s is the transition period of American Physics，and the operation mode of the center of theoretical physics of University of Michigan has become a typical case in the history of physics construction.This paper summarizes and analyzes the case，hopes to have a beneficial enlightenment to the construction of our country's current physics research team and the workshop of physics.

Prospect and idea on the construction of online open physics courses group

NI Mu-cui，ZHANG Han-zhuang

College Physics. 2017, 36(7): 51-55. doi:10.16854 /j.cnki.1000-0712.2017.07.013

Abstract ( 877 )

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The background and development status of online open courses and courses group are reviewed. The

necessity of construct online open physics courses group is proposed. Online open physics courses group have distinct

advantages such as clear objects，systematic courses and high-quality resources. The main idea and suggests

about how to project resources of physics courses group are given.

Teaching RL transient state processes using circuit model equivalent transformation

ZHAO Qiang，SUN Dian-ping，GUO Chao-xiu

College Physics. 2017, 36(7): 56-58. doi:10.16854 /j.cnki.1000-0712.2017.07.014

Abstract ( 1075 )

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Using circuit model reconstruction and equivalent transformation，the RL circuit transient process is concisely analyzed with the help of meaningful physical models. When the final and initial states are selected as the reference ones，the full state response of RL circuit is illustrated as 1) a constant coefficient decay process and 2)the superposition of the zero state and the zero input state，respectively. Meanwhile，according to the research of the modern cognitive theory，this teaching process is helpful to active the information from memory，encode information in meaningful ways，form robust knowledge，and consequently，improve the teaching effect.

Application of“Rotation”in physics experiments

CAO Zhen-xin，NING Chang-chun，WANG Ya-ping，ZHANG Hui-jie

College Physics. 2017, 36(7): 59-61. doi:10.16854 /j.cnki.1000-0712.2017.07.015

Abstract ( 1301 )

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Through the analysis of several physics experiments，the paper describes the application of the“Rotation” in several physics experiments. The focus of the paper is on the role that“rotation”plays in the realization of the experiment idea.

Video analysis on two kinds of pendulum

XUE Hui-ling， JIA Yu，LI Zhi-jian

College Physics. 2017, 36(7): 62-64. doi:10.16854 /j.cnki.1000-0712.2017.07.016

Abstract ( 1099 )

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By using the Tracker video analysis and modeling tool，the angular displacement date of a large-angle pendulum and a conical pendulum are analyzed. The law of pseudo-periodicity in a large-angle pendulum is obtained，and the formula of centripetal acceleration is precisely proved.

The relativity of electrostatic field and magnetic field

YU Mo-nong，ZHOU Min，SHI Qing-fan，XING Yan-xia

College Physics. 2017, 36(7): 65-69. doi:10.16854 /j.cnki.1000-0712.2017.07.017

Abstract ( 1277 )

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The electric field and the magnetic field have different forms but the same essence. For different inertial systems，they can achieve mutual transformation，which follow the fundamental principles of mechanics. With the aid of special relativity and basic law of mechanics，this paper attempts to analyze the mutual transformation process and forms of the electric field and magnetic field in a more intuitive way， thus the essence of the electric field and magnetic field coming from the same material can be understood more deeply.

The experiment of measuring electromagnetic radiation by using induction coil

WANG Yu-sen，GAO Hong，LI Hua，WANG Mei，ZHANG Jun-ying

College Physics. 2017, 36(7): 70-73. doi:10.16854 /j.cnki.1000-0712.2017.07.018

Abstract ( 1312 )

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In recent years，electronic devices have been widely spread. Also，the fact that electromagnetic radiation　can do harm to our health has attracted more attention. Thus，the methods of measuring electromagnetic radiation are studied by many people. In this paper，we introduce the method of induction coil. By carrying out different experiments，we prove successfully the feasibility of the method. Finally，a three-dimensional magnetic field sensor is fabricated in terms of this method

Computer simulation of fractal tree structure

FAN De-li，JIANG Shao-zhou，LIN Da-bin

College Physics. 2017, 36(7): 74-76. doi:10.16854 /j.cnki.1000-0712.2017.07.019

Abstract ( 1332 )

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Using the diffusion limited aggregation model in Cartesian grid，equilateral triangle mesh and hexagonal mesh，we simulate the tree fractal structures. For avoiding the impact of the direction of the movement，we simulate the metal ball movement in the electro fields to generate the fractal structures. The results of fractal dimensions of different charge densities are obtained by using the Sandbox method. The fractal dimension decreases when the charge density increases. It confirms to the experimental result

Interpretation of Fourier transformation connecting real lattice and reciprocal lattice spaces

XU Fu-zong，SHI Si-qi

College Physics. 2017, 36(7): 77-81. doi:10.16854 /j.cnki.1000-0712.2017.07.020

Abstract ( 2304 )

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Due to involving some advanced mathematics knowledge，the Fourier transformation connecting the real lattice and reciprocal lattice spaces is one of difficult points in teaching solid state physics. Based on the periodical characterization of crystal structure and the simple mathematical derivation，we attempt to give a detailed interpretation on the Fourier transformation process，in which the physical connotation is paid close attention.

College Physics. 2017, 36(7): 82.

Abstract ( 641 )

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