Table of Content

15 June 2024 Volume 43 Issue 5

  

Berry curvature in solid state physics

YUAN Zhe, ZHOU Shi-ming

College Physics. 2024, 43(5):  1.  doi:10.16854/j.cnki.1000-0712.230289

Abstract ( 591 )   PDF (808KB) ( 481 )  

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Periodic potential and Bloch^,s theorem in solid makes Berry curvature different from that in continuousmedia. The Bloch wave function of the n-th energy band at k point in Brillouin zone has its modulation factor unk(r), and the corresponding Berry curvature is given by Ωnk=×Ank with Berry connection Ank=〈unk|ik|unk〉. In the presence of inversion and time reversal symmetries, Berry curvature vanishes at in any k point of Brillouin zone. With broken inversion and time reversal symmetries, or with spin-orbit coupling, or the band degeneracy, Berry curvature can be nonzero. Berry curvature induces an anomalous velocity perpendicular to external electric field, which in turn leads to the intrinsic anomalous Hall effect, the intrinsic spin Hall effect and the nonlinear Hall effect. This work is helpful for a better understanding of Bloch wave function and Boltzmann transport equation.




From the Lissajous figure to the periodic orbits of particles in the background of black holes

WEI Shao-wen1, FU Chun-e2

College Physics. 2024, 43(5):  6.  doi:10.16854/j.cnki.1000-0712.230246

Abstract ( 221 )   PDF (974KB) ( 209 )  

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Starting from the classical Lissajous figures formed by the simple harmonic vibrations in the transverse and longitudinal directions under the classical Cartesian coordinate system, we study the Lissajous figures formed by the vibrations in the radial and angular directions under the polar coordinates. The features of the Lissajous figures are analyzed when the equilibrium point is located at the origin of polar coordinates and the equilibrium point moves in a circular motion. These results are further extended to the periodic orbits formed by the bound motion of particles in the background of black holes. This further enriches and expands our knowledge and understanding of the Lissajous figures.




Application of Fermi^,s golden rule in teaching of absorption and emission of solid physics

HU Yan-qing

College Physics. 2024, 43(5):  9.  doi:10.16854/j.cnki.1000-0712.230228

Abstract ( 193 )   PDF (792KB) ( 166 )  

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 Fermi^,s golden rule is a theory describing the probability of wave function of a system changing from one characteristic state to another, which can well elaborate the absorption and emission of solid luminescent materials. However, the derivation process of Fermi^,s golden rule is relatively complex, and students do not understand the results of the derivation, which affects the follow-up teaching progress and the overall teaching quality. In this work, the derivation of the Fermi^,s golden rule formula is reviewed. Based on this rule, an energy transfer rate between electric dipoles of a donor-acceptor system is derived, which demonstrates that the energy transfer between the electric dipoles is inversely proportional to both the square of dielectric constant and the sixth power of coupling distance. This result provides a theoretical basis for regulating the energy transfer rate between electric dipoles. In addition, an ion dipole-atom dipole energy transfer model is established according to the Fermi^,s golden rule formula and their energy transfer rate is derived. The proposed theory clarifies the energy dissipation mechanism of excited states of emitting centers, and provides effective measures to enhance the emission efficiency. This application example enables students to better understand the physical meaning of the Fermi^,s golden rule.



On the Shrinkage time and upper end motion of magic springs

YU Feng-jun1, ZHANG Xi-wei1, TANG Zhen-jie1, JU Lin, TIAN Jun-long2

College Physics. 2024, 43(5):  13.  doi:10.16854/j.cnki.1000-230251

Abstract ( 208 )   PDF (839KB) ( 244 )  

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 Several issues related to the study of magic springs are explored and clarified. A model of pre retracting force spring is established and its deformation law is derived. According to the motion theorem of the center of mass, the time for the spring to shrink to the original length, the equations of motion of its upper end and the speed formula are derived when the spring falls freely, and the applicable conditions of the contraction time formula in some current literatures are given. Research has shown that for the magic spring commonly used in demonstrations, during the contraction phase of free fall, its upper end does not move uniformly in a straight line



The motion of an electron emitting electromagnetic radiation around atomic nucleus

GUO Xue-peng

College Physics. 2024, 43(5):  19.  doi:10.16854/j.cnki.1000-0712.230258

Abstract ( 259 )   PDF (792KB) ( 575 )  

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The accelerative motion of electrons around the nucleus radiates electromagnetic waves that make atoms unstable. In this paper, the differential equation of the radius of electron motion is established on the assumption that an electron moves in a uniform circle around the nucleus for a short time. The trajectory equation of electron in polar coordinate system and the time expression of electron falling to the nucleus are obtained. It is concluded that an electron moves in a spiral around atomic nucleus and falls to the nucleus in about 10-10 s.



Derivation ofthe De Broglie matter wave equation

WANG Yang

College Physics. 2024, 43(5):  22.  doi:10.16854/j.cnki.1000-0712.230226

Abstract ( 371 )   PDF (762KB) ( 461 )  

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The equation for the momentum and the wavelength for the matter wave is derived in two intuitive ways. The first way is to use the Lorentz transformation to obtain the inherent time difference between the head and tail of the moving particles, and then obtain the corresponding wavelength for the material wave through its phase difference and the length of the particle occupied in space. The second way is to obtain the equation by calculating the traveling wave adapted to the phase change of the particle. These two derivation methods are intuitive and helpful to beginners to understand the physical image of the matter wave.



Discussion on some problems of solar cells

ZHANG Zhi-ming1, 2, HE Shan1, SUN Tie-tun3

College Physics. 2024, 43(5):  25.  doi:10.16854/j.cnki.1000-0712.230209

Abstract ( 178 )   PDF (763KB) ( 186 )  

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The following three problems on solar cells are studied in this paper： It is well known that the key element of a solar cell is a PN junction. However, the so called current-voltage characteristics curve (I-U curve) of a solar cell looks very differently with that of a normal PN junction, why? How does the I-U curve of a solar cell change exactly? How do the output current, output voltage, and output power of a solar cell change with the load resistance? The study on these problems has important significance in design and application of solar cells. The research results are as follows: The reason of first problem that the so called I-U curve of a solar cell is, in fact, the I-U curve of the load resistance in a solar cell circuit, not the I-U curve of the PN junction in the solar cell. The answerHYPERLINK"javascript:;" to the second problem is that the current monotonously decreases with increasing the voltage. The answerHYPERLINK"javascript:;" to the third problem is that for a solar cell circuit, with the increase of the load resistance, the output current monotonously decreases, and the output voltage monotonously increases, while the output power does not change monotonousl. There exists a maximum output power which correspods to an optimal load resistance.



Experiment system for photoelectric effect based on NI myDAQ data acquisitor

LIAO De-ju, FENG Rao-hui, CUI Xin-tu, SHEN Han, HUANG Zhen-cheng, FANG Yi-zhong, PANG Xiao-ning

College Physics. 2024, 43(5):  29. 

Abstract ( 115 )   PDF (1071KB) ( 163 )  

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 A physics experiment teaching system constructed by using general purpose instruments can improve the freedom of equipment usage, highlight physical principles behind the experimental measurements, assist students in better experiment experiences with scientific research thinking, and improve the quality of innovation training. A photoelectric effect experiment system based on LabVIEW platform is designed, which uses fA-grade high-precision electrometer transimpedance amplifier to detect photocurrent and uses NI myDAQ to collect data. With this system, quantitative real-time record can be completed. Visual display the variation of photocurrent IKA with anode voltage UKA，multiple IKA-UKA characteristic curves with different parameters are displayed in the same coordinate. The cut-off voltage U0 of different spectra lines (frequency ν) is measured. The U0-ν fitting curve and Planck constant h are obtained by data analysis module. The system is used to measure a set of spectral lines, get h=(6.63±0.28)×10-34 Js. It is consistent with the recognized value h0=6.62606896×10-34  Js,  and the relative error is about 0.40%. The results show that the measured results of the system agree well with the recognized value of Planck constant.



Computer-aided instruction in analytical mechanics

HE Hong-bin1, ZHENG Hua1, ZHANG Wen-chao1, WANG Xin-gang1, ZHU Li-lin2

College Physics. 2024, 43(5):  33.  doi:10.16854/j.cnki.1000-0712.230187

Abstract ( 148 )   PDF (876KB) ( 149 )  

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Computer-aided instruction can be complementary to the traditional teaching. The effective combination of them can help students to understand the knowledge which is difficult.  Therefore, we stimulate students’ interest in learning and improve the teaching quality. Then, we introduce the attempts of computer-aided instruction by using two typical problems, i.e., Rutherford scattering and two  body collision, in analytical mechanics. 






Construction and practice of ideological and political of laser principle course based on trinity education concept

College Physics. 2024, 43(5):  45.  doi:10.16854/j.cnki.1000-0712.230279

Abstract ( 129 )   PDF (833KB) ( 204 )  

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The construction of ideological and political of professional course is an important strategic measure for the original foundation of higher education in new era. It has gradually reached a consensus in the higher education circle and been vigorously promoted and practiced, which has also brought new ideas and challenges for curriculum education. As a basic course of physics, electronics and optics, it is urgent and important to carry out ideological and political education in laser principle course. Guided by the three-in-one education concept of value shaping, knowledge imparts and ability cultivation, in this paper the implementation path of laser principle course combining ideological and political construction is extracts in three aspects of teaching content, teaching mode and teaching effect evaluation. The preliminary exploration and practice are carried out to realize the organic integration of ideological and political education as well as course teaching.



Twomethods of calculating conjugate momentum in Jacobi coordinates

LI Jin-lin, CAO Zhou-jian

College Physics. 2024, 43(5):  45.  doi:10.16854/j.cnki.1000-0712.230238

Abstract ( 184 )   PDF (812KB) ( 217 )  

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Hamiltonian theory is an important teaching content of theoretical mechanics and celestial mechanics. Canonical coordinates and canonical coordinate transformations are key concepts in Hamiltonian theory and important technical means for solving dynamic equations. The N body problem describes the behavior of N objects or celestial bodies moving under the gravitational interaction. The N body problem is one of the key and difficult points in the teaching of theoretical mechanics and celestial mechanics. In addition to ten classical conserved quantities, Jacobi coordinates are another important means and method for the N body problem. Ordinary textbooks only talk about the physical meaning of Jacobi coordinates. In this paper, the specific transformation relationship between Jacobi coordinates and inertial coordinates is given, and then the conjugate momentum corresponding to Jacobi coordinates is given by using the method of canonical coordinate transformation. This result not only complements the knowledge of Jacobi coordinates about canonical coordinates, but also gives a good practical example of canonical coordinate transformation. In this paper, the trick of canonical coordinate transformation are pointed out through two different methods of calculating conjugate momentum of Jacobi coordinates. These contents can be a useful supplement to the classroom teaching of theoretical mechanics and celestial mechanics.




Study on the flow characteristics of liquid coatings on horizontally rotating cylinders

SHEN Xiao-yini, HONG Yi-qian, HUA Yi-hang, LI Yao, WANG Ji, TANG Shi-wei

College Physics. 2024, 43(5):  50.  doi:10.16854/j.cnki.1000-0712.230199

Abstract ( 134 )   PDF (992KB) ( 135 )  

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The current carrying capacity of liquid coating on rotating cylinder surface is an important parameter for fluid control and process design in industrial applications. The purpose of this paper is to study the influence of the viscous fluid load on the surface of a rotating rod on its rheological properties, rod speed, rod radius and viscosity, and to analyze the fluid load on a rotating rod under different conditions. Through the experiment of variable control on the fluid with different characteristics of the rotating rod system, the experimental data consistent with the theoretical prediction are obtained,  and the relationship between the carrying capacity of the viscous fluid on the rotating rod and the rotation speed of the rod, the radius of the rod and the viscosity of the fluid is demonstrated. Our research has laid the experimental and theoretical foundation for the optimization of equipment performance in industrial production.



The motion of vicious liquid film coating on a horizontal hotating cylinder

LIN Yun-qian, LEI Jia-rui, MA Yu-han

College Physics. 2024, 43(5):  55.  doi:10.16854/j.cnki.1000-0712.230270

Abstract ( 140 )   PDF (885KB) ( 155 )  

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In this paper, the motion of viscious liquid outside a rotation cylindrical rod is studied. By conducting controlling variable experiments, Moffat^,s theoretical formula is verified to some extent. It is proposed that the inertial effect at a relatively high Reynold number (>10) causes the difference between theoretical and experimental results. The periodic changes in cross-sectional shape of liquid film with respect to angular velocity is furthur studied, and images of the shape of liquid film at different angular velocities are obtained. Meanwhile, the phenomenon of forming liquid rings along the axial direction of cylindrical rod is quanlitatively studied, and the relationship between the number of rings and several factors is given.



Water vapor transport in porous organic fabrics in indoor environment

ZHOU Rui1, WU Si-yuan1, MA Qi-bo1, CHEN Jin-yu1, FANG Ai-ping1, TIAN Peng-bo1, FENG Jun1, JIANG Chen-wei 1, LIU Li-na2, ZHANG Xiu-xing3, WANG Xiao-li1

College Physics. 2024, 43(5):  60.  doi:10.16854/j.cnki.1000-0712.230212

Abstract ( 96 )   PDF (1053KB) ( 74 )  

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Starting from the problem of drying clothes in the dormitory, the clothes are abstracted into organic fabrics, and the drying process is also simplified into a transportation process. The porous media model and the theory of transportation process are comprehensively applied, combined with COMSOL multi-physics simulation software, the drying process is given too. The surface temperature, the relative humidity of the porous medium and the drying time are affected by many factors, which have certain reference value for the study of the theory and application of the transport process. 



Evolutionary properties of Airy wave packets and their applications in optical communications

LIAO Yan-juan1, ZHANG Lin1, 2

College Physics. 2024, 43(5):  68.  doi:10.16854/j.cnki.1000-0712.230221

Abstract ( 167 )   PDF (919KB) ( 126 )  

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 The eigenwave functions of the general linear potential field and the tent-type linear potential field are solved, the free evolutions of these two Airy wave packets are analyzed, and the propagation properties of Airy wave packets used as optical information carriers are investigated in the media. Firstly, the core form of the solution of the intrinsic wave function in the general linear potential field can be expressed as the standard Airy function, and the characteristics of the soliton and self-accelerating properties of Airy wave packet propagating in free space are discussed. Then the eigenwave function of the bidirectional airy wave packet under the tent type linear potential is calculated and the accelerated interference diffusion behavior of the bidirectional Airy wave packet under different parameters is discussed. The solutions of the above two kinds of Airy wave packets are applied to the dielectric transmission problem of electromagnetic field. The accelerated transverse deflection and transverse interference of the electric field of Airy wave packets in the medium are discussed.



Design of visualized numerical experiments for energy band in solid-state physics

GUO Qi-he, CHENG Qian-qian, DU Tao-yuan

College Physics. 2024, 43(5):  75.  doi:10.16854/j.cnki.1000-0712.230253

Abstract ( 167 )   PDF (793KB) ( 164 )  

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Considering the lack of discussion of the crystalline energy band structure in real space in the commonly used solid-state physics textbooks, we take the one-dimensional periodic potential as an example to introduce how to obtain the energy band under any atomic-chain potential in the seminar teaching. Design of visualized experiments will help students to build a physical picture for band formation in solid-state systems. It is of great reference value for related condensed matter theory courses.



γ-γ Coincidence Measurement experiment based on Pixie-Net digitizer

GE Hao-yu, YANG Jia-lin, LIN Zhe-yang, LOU Jian-ling

College Physics. 2024, 43(5):  79.  doi:10.16854/j.cnki.1000-0712.230239

Abstract ( 138 )   PDF (994KB) ( 172 )  

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With the development of nuclear physics technology, traditional electronic modules are no longer able to meet the increasingly demanding requirements of nuclear physics experiments. Digital instruments have been widely used due to advantages of high integration and flexible data processing. We attempt to use the Pixie-Net digitizer for the γ-γ coincidence experiment using the NaI and CeBr3 detectors in order to simplify experimental equipment and to improve teaching effectiveness. The results show that after optimizing the parameters of the digitizer based on the pulse shapes and correcting the difference in angular correlation coefficient caused by the size of the detector and radiation source, the activity error of the radioactive source between the test value and the theoretical value is less than that from the β-γ coincidence method based on traditional electronics.