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Table of Content
21 April 2018 Volume 37 Issue 4
Can use the equipartition theorem in the transition state of Brownian motion?
BAO Jing-dong
College Physics. 2018, 37(4): 1-4. doi:
10.16854 /j.cnki.1000-0712.170493
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The Brownian motion is a basis subject in non-equilibrium statistical physics. However，the current textbooks have inappropriate problems for explaining this subject，namely，by using the particle's coordinate to multiply the Langevin equation and then averaging over the two sides of the equation，thus the time-dependent mean squared displacement of the force-free particle is calculated. We think that the expression proposed by the moment method of this kind is not rigorous and the explanation for the mechanism of ballistic diffusion motion is also incorrect. Based on the accurate solution of the linear Langevin equation，this paper proposes the expressions of variances of velocity and coordinate of the particle. We also modify the moment method used in the present textbooks and make it give the correct result of the mean squared displacement of the force-free particle.
Realization of quantum XOR gate by using quantum game of two coins
WANG Qing-liang，REN Heng-feng
College Physics. 2018, 37(4): 5-7. doi:
10.16854 /j.cnki.1000-0712.170433
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1527
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First of all，it is introduced that quantum strategies are successful more than classical ones in basic knowledge of quantum game theory of two coins. Secondly，based on the logical relationship and the truth table in classical Exclusive-OR gate，and combing with quantum theory，quantum Exclusive-OR gate is defined. Lastly，we put forward a new operable scheme on how to realize quantum XOR gate using the model of two-coin quantum game.
Derivation of reflection wave，transmission wave and half wave loss of mechanical waves
DING Gui-jun
College Physics. 2018, 37(4): 8-10. doi:
10.16854 /j.cnki.1000-0712.170048
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3363
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We have derived the expressions of reflection wave and transmission wave when a mechanical wave reaches perpendicularly an interface of two media. It is shown that half wave loss appears when a mechanical wave propagates from sparse medium to dense medium. Our analyses are helpful to understand the key concepts and physical laws of the interfacial behavior of mechanical waves.
Study of the input resistance in the circuit without independent source
WANG Wei-gang1，TU Zhen-zhen2
College Physics. 2018, 37(4): 11-15. doi:
10.16854 /j.cnki.1000-0712.170415
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1465
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615
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The one port network which only contains resistors or controlled sources，not including independent source，can be divided into pure resistors circuit and controlled sources circuits. As to pure resistors circuit，we propose a method of“searching roads by marking points”. As to the circuit with controlled sources，it can be resolvedby the external excitation method and internal excitation method. External excitation method includes the traditional method of “calculating current by inputting voltage”and“calculating voltage by inputting current”. As to internal excitation method，we also propose a new method named“open-short”.
Potential induced by one-dimensional arbitrary charge distribution
RU Guo-ping
College Physics. 2018, 37(4): 16-22. doi:
10.16854 /j.cnki.1000-0712.170215
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1191
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Three methods such as potential superposition，integration interval transformation and doping moment，are introduced to calculate the potential induced by one-dimensional arbitrary charge distribution，taking a MOS structure with non-uniformly distributed oxide charges as an example. The equivalence of the three methods is verified. As a focus，the doping moment method is employed in C-V characterization of a non-uniformly doped n+p junction and threshold voltage calculation of MOSFETs with a non-uniformly doped channel. The principles of varactors and retrograde doping in MOSFET are discussed.
Several physical considerations about unidirectional optical transmission and reciprocity principles of optics
GAO Hua1，2，WEI Guo-guo1，XU Ling-ling3，ZHANG Qiang3
College Physics. 2018, 37(4): 23-26. doi:
10.16854 /j.cnki.1000-0712.170374
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1700
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Unidirectional optical transmission，also named optical diode，it permits optical wave to transmit from one incident direction while prohibit it when wave incidents from the reversed direction. It is one of the most important optical elements of the optical calculation and optical connections. While in linear and non -magnetic material system，the optical wave has to obey the reciprocity principle of the optics and the propagation path must be reversible. So it raises the questions that: Whether the unidirectional transmission can be obtained in linear and non -magnetic material system? If the answer is yes，what is the obtaining way? And what is the relationship between the reciprocity principles and the unidirectional transmission in linear and non-magnetic material system? In this paper，the unidirectional transmission effect is obtained at multiple frequencies based on the guided mode resonance occurred in the substrate of a dielectric grating inspired by grating diffraction. And taking it for an example，we prove that in linear and nonmagnetic system，asymmetric optical transmission is also available and the reversibility of light is still effective. Besides，through further analysis，it is found that in this kind of linear and on-magnetic system，the unidirectional optical transmission is attributed to the asymmetric propagation channels of the optical path.
Exact solution of three-dimensional Schrdinger equation for generalized Kratzer potential
FU Mei-huan
College Physics. 2018, 37(4): 27-30. doi:
10.16854 /j.cnki.1000-0712.170424
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1273
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Using super - symmetric quantum mechanics arguments，the shape invariance of the generalized Kratzer potential is discussed，and its energy eigenvalues are calculated. Both the traditional Kratzer potential and the modified Kratzer potential are the special cases of the generalized Kratzer potential. On this basis，the exact eigenvalues of the diatomic molecules such as CO and NO for various values of radial quantum number nr and angular quantum number l are calculated numerically.
Two new approximate formulas of energy levels in finite depth symmetric square potential well
HU Zong-yuan
College Physics. 2018, 37(4): 30-33. doi:
10.16854 /j.cnki.1000-0712.170345
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1542
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745
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By introducing an angle parameter，we get two new approximate formulas of energy levels in finite depth symmetric square potential well，and error analysis is carried out. The two new approximate formulas are applicable to low energy and high energy levels respectively. From the comparison with numerical results，we find that the two approximate formulas obtained in this paper have higher accuracy and better applicability.
Study of the survival time of droplet on the liquid surface under vertical excitation
WU Ling1，XUN Zhi-peng1，QIU Liang1，YAO Lei2
College Physics. 2018, 37(4): 34-36. doi:
10.16854 /j.cnki.1000-0712.170311
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1098
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423
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Drop in liquid surface of vertical excitation is possible to stay in the surface for a long time. Based on the experiment，we study the effects of various factors on the survival time of the droplets. The results show that the droplets may survive for a long time under appropriate values of the driving frequency，driving amplitude and liquid drop height. In addition，the survival time of the droplets depends on the liquid concentration.
Numerical simulation of capillarity in triangular capillary
LU Li-ping，WEI Liang-shu， JIANG Xi-ping
College Physics. 2018, 37(4): 37-40. doi:
10.16854 /j.cnki.1000-0712.170140
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1446
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Based on the surface tension of curved liquid surface，the capillarity in triangular capillary is studied. Using Matlab numerical simulation，the surface tensions of two kinds for liquid surface with different contact angle functions，the height and velocity of liquid in the capillaries are calculated. The results show that as the same caliber，the height in triangular capillary is larger than that in circular capillary. Considering the impact of friction f = 1.732×10-2y N the velocity of liquid in capillary is consistent with the actual situation.
Method and setup for determining the polarization parameters of optical elements
LIU Ming-qiang1，2
College Physics. 2018, 37(4): 41-46. doi:
10.16854 /j.cnki.1000-0712.170099
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1539
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Based on the polarized light theory，the polarization change of a linearly polarized light after reflected from one or more optical elements is investigated theoretically. It is found that through appropriately setting the amplitude reflection coefficients ( rs ，rp ) of optical elements，the polarization deterioration of the polarized light induced by several optical elements can be lower than that induced by one element. A method for determining the incidence plane of a light ray is given. In the experimental setup，the polarization maintaining ratios of two 780 nm high-reflection mirrors ( with dielectric and metallic coatings，respectively) at 45o( for both polarization angle and incidence angle) are determined to be 1 000 ∶ 1 and 40 000 ∶ 1，respectively. The amplitude coefficient ratio rp /rs and phase difference δ are in good agreement with those measured by the ellipsometry. This method and setup can， on the one hand，provide theoretical and experimental guidance for polarization-related physics experiments，and on the other hand，can be applied in scientific research and engineering fields for in-situ measurement of the reflection parameters ( rp /rs and δ) and polarization maintaining ratio of optical elements.
Significance of academic ability training for talent students in physics ———Boling class of physics，Nankai University，as an example
WU Qiang，YU Hua，BO Fang，LIU Zhi-bo，LIU Song-fen，LI Chuan-yong
College Physics. 2018, 37(4): 47-50. doi:
10.16854 /j.cnki.1000-0712.170472
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1881
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544
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In this paper，we discuss the significance of academic ability training for talent students in physics， using Boling Class of Physics，Nankai University，as an example. We introduce our opinions to the academic training system: pay more attention to academic foundation，emphasize academic spirit，increase academic interest，improve team spirit and cooperation ability，master osmotic learning method，and cultivate basic scientific research ability. We also introduce our practices: the relevant courses，as the backbone，coupling with the related academic activities，formed the academic ability training system for the outstanding physics students. To evaluate the results of this training system，we also carry out research for some related issues.
Correction and analysis of transmission line equations of the lightning electromagnetic field
YE Gen
College Physics. 2018, 37(4): 51-53. doi:
10.16854 /j.cnki.1000-0712.170377
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1133
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Considering the finite conductivity of the earth，the horizontal electric field of the near earth is more significant influence on the power cord and electronic equipment. Therefore，the earth conductor is supposed to be a noble ideal，in this case，the transmission line equation of the lightning electromagnetic field is derived，which needs to be revised. We use the modified transmission line equation and the various parameters of the earth and get the spread of lightning overvoltage on the transmission line. The impact on the limited earth conductivity is discussed and analyzed.
Study on the range of free flight section of ballistic missile
YU Lan，YANG Zong-xian
College Physics. 2018, 37(4): 54-57. doi:
10.16854 /j.cnki.1000-0712.170600
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1804
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The range formula of free flight section of ballistic missile is derived by using the elliptic equation. When the initial velocity of the free flight section is given，the maximum range and corresponding trajectory inclination angle are deduced by the range formula. And several examples of estimating ballistic parameters are given.
The study of single-beam optical tweezers in theory and experiment
ZHAO Zi-jin1，XU Chun-yu1，WANG Yue-fei2，LV Tian-xiang1，SUN Mei-yu1
College Physics. 2018, 37(4): 58-63. doi:
10.16854 /j.cnki.1000-0712.170124
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1352
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A single-beam optical tweezers experimental system is presented，which can be used to trap some tiny particles stably and also realize microscopic imaging. Based on this system， the dynamic capture process of single silica microspheres is studied.It is found from experiments that the focal plane of the objective lens and the imaging plane of the CCD must be in a same plane when the particles are captured and imaged at the same time.In addition， the effect of the numerical aperture of the focusing objective lens and the power of the laser for stable trapping of the particles are also found in the experiment.Both experimental results and theoretic analyses indicated that the larger of the numerical aperture and the greater of the laser power leaded to enlarge the capture force of the particles，so the particles can be stably captured.This study is helpful in the field of college physics teaching and biological micro-manipulation.
Simulation analysis of triangular prism deviation angle
LI Xuan，ZHANG Xue
College Physics. 2018, 37(4): 64-67. doi:
10.16854 /j.cnki.1000-0712.170515
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3661
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The formula of the deviation angle is deduced. The influence of the prism angle and the refractive index on the relationship between the angle of incidence and the angle of refraction are discussed. The angle of inclination and the angle of incidence are discussed. The relationship between the vertex angle and the refractive index，and the physical meaning of the curve are expounded. Finally，the minimum deflection angle is studied.
The measurement of the space magnetic field based on the Faraday magneto-optical effect
YE Zi-mu1，ZHANG Lai1，DONG Guo-bo2，XIONG Chang2，TANG Fang2，LI Hua2
College Physics. 2018, 37(4): 68-73. doi:
10.16854 /j.cnki.1000-0712.170076
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1970
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The Faraday effect is a kind of phenomenon that may cause the rotation of the optical vector when the linearly polarized light is passing through a magneto-optical medium under the influence of an external magnetic field. The angle of rotation of the polarization direction of the light is linearly proportional to component of the magnetic field along the direction of propagation of the light wave. In this paper，the space magnetic field is measured innovatively with the Faraday magneto-optical effect，it can reduce the measurement error of the goniometer and find the exact position of extinction by using the method of the penumbra. The magnetic induction intensity B = 0. 2876 mT of the magnetic field in the laboratory environment is measured and the magnitude of the magnetic declination is θ = 7.6884°. The relative error of the magnetic induction intensity is ηB = 4.6% and the relative error of the magnetic declination is ηθ = 9.8% compared with the data measured using the magnetoresistive sensor.
The numerical solution of nuclear magnetic resonance based on Bloch equations
ZHANG Xin-jie，CAO Yang，SUI Wen-bo，XI Li，YANG De-zheng
College Physics. 2018, 37(4): 75-81. doi:
10.16854 /j.cnki.1000-0712.170382
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1443
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699
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The nuclear magnetic resonance ( NMR) has become one of the most effective tools to study the structure，dynamic processes and physical properties of molecular science，material science，life science and some other fields. We focus on the study of nuclear magnetic resonance according to the Bloch Equation and the related experimental parameters，such as resonance frequency and relaxation time. Meanwhile，the pulse sequences including Single Pulse，Inversion Recovery，Spin Echo，CPMG and etc are simulate. Thus we reveal consequently the physical origins of different pulse sequences.
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