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Principle and applications of frustrated total internal reflection SHAN Xi-chen, DING Ruo-yu, SUN Xu-bo, ZHANG Wen-kai College Physics    2023, 42 (12): 13-.   DOI: 10.16854 /j.cnki.1000-0712.230225 Abstract （654）      PDF（pc） （945KB）（631）       Knowledge map    Save Total internal reflection is the phenomenon which light is reflected totally on the surface when light is incident from a dense medium to a thin medium at an angle greater than critical angle. In total internal reflection, evanescent waves are generated on the side of the thin medium. Evanescent wave is a surface wave that propagates along the surface of media and its amplitude decreases exponentially with the increase of penetration depth. When the medium of the third layer with a higher refractive index than the second layer gets close to the boundary between the first and the second layer, the medium will interact with evanescent waves in the second layer, resulting in partial light reflected by total internal reflection at the interface of the first and second layer penetrating into the third layer medium, and this phenomenon is called frustrated total internal reflection. In recent years, frustrated total internal reflection has been applied in many fields and has attracted extensive attention. In this paper, firstly evanescent wave and frustrated total internal reflection and theories of them are introduced briefly, and the relationship between transmittance and width of the thin medium, refractive index of medium and incident angle are simulated by MATLAB. Secondly, two experimental schemes to verify the frustrated total internal reflection and some applications depending on in several fields are shown. Related Articles | Metrics | Comments（0）

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College Physics    2024, 43 (8): 1-.   DOI: 10.16854/j.cnki.1000-0712.240138 Abstract （587）      PDF（pc） （448KB）（582）       Knowledge map    Save Related Articles | Metrics | Comments（0）

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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 （569）      PDF（pc） （808KB）（457）       Knowledge map    Save 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. Related Articles | Metrics | Comments（0）

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Discuss more about half-wave loss and the interference of thin film LIU Jia-ming College Physics    2024, 43 (02): 16-.   DOI: 10.16854 /j.cnki.1000-0712.230052 Abstract （563）      PDF（pc） （627KB）（580）       Knowledge map    Save There are four parts in this paper. First, more discussions about the formulas and the physical situations are presented to the article “Condition of half-wave loss when light is emitted from optically denser medium to optically thinner medium”, which was published in this magazine not long ago. Second, some views about half-wave loss in that article are discussed. It is pointed out that there is usually no half-wave loss when the light with polarization parallel to the plane of incidence shooting on the medium with small refractive index from the medium with large refractive index and the ratio between their refractive indexes is huge. Third, the quantitative analysis of the interference of thin film is presented. It is shown that the results from the formulas in the textbook are usually close to the results from the Fresnel formula. Fourth, it is pointed out that the formula of the interference of thin film for the dark lines in the textbook is right, but to the bright lines, it will be absolutely wrong in some cases.  Related Articles | Metrics | Comments（0）

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Study on quantum tunneling of one-dimensional  triple square potential barriers LI Hai-feng, CHEN Kang-kang, WANG Xin-mao College Physics    2024, 43 (02): 1-.   DOI: 10.16854/j.cnki.1000-0712.230189 Abstract （509）      PDF（pc） （572KB）（480）       Knowledge map    Save In this paper, the quantum tunneling characteristics of onedimensional symmetric triplesquarepotential barriers are studied by solving the stationary state Schrdinger equation in different areas. Moreover, the exact expression of the transmission coefficient is analytically attained, and the dependence of the transmission coefficient on the barrier width, barrier spacing, and the incident energy of the particle is numerically simulated. Furthermore, the results show that when different potential barrier widths or different incident energies of the particle are taken, the periodic oscillation phenomenon of the transmission coefficient with the increasement of the barrier spacing is exhibited. Comparing with one-dimensional symmetric double barriers, the periods of the transmission coefficient oscillating with the barrier spacing increases are the same. However, the oscillation of the triple square potential barriers is more intense and the amplitude is larger. At a period, it is a bimodal curve for the triplesquare potential barriers, while it is a unimodal curve for the double-square potential barriers. This characteristic provides theoretical guidance for designing novel nanodevices and resonant tunneling quantum devices. Related Articles | Metrics | Comments（0）

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Transltor,s afterwords and tribute to professor Liang Canbin ———Penned for the English edition publication of Differential Geometry  and General Relativity (Volume 1) Jia Wei-zhen College Physics    2023, 42 (12): 55-.   DOI: 10.16854/j.cnki.1000-0712.230397 Abstract （487）      PDF（pc） （1181KB）（407）       Knowledge map    Save From the translators perspective, this article recounts the whole process of planning and preparing the English edition of Differential Geometry and General Relativity (Volume 1) up to its publication. It recollects my interactions with Professor Liang Canbin during this period, serving as a remembrance and heartfelt tribute to the esteemed Professor Liang. Related Articles | Metrics | Comments（0）

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The terminal velocities of spherical raindrops in still air and the usage conditions of Stokes viscous resistance SHAO Yun College Physics    2024, 43 (3): 25-.   DOI: 10.16854/j.cnki.1000-0712.230210 Abstract （472）      PDF（pc） （847KB）（194）       Knowledge map    Save The article uses the Wallis formula, which is more accurate for the air resistance coefficient of smooth spheres, to gradually analyze and calculate the terminal velocities of spherical raindrops with different radii in still air at 20 ℃, and compares them with some actual measurement values, pointing out the reasons for the differences. The article also takes Wallis formula as the standard, and estimates that under the condition of not too high precision requirements, the Stokes- first power viscous resistance formula of a smooth sphere can roughly be applied to the Reynolds number interval with Re<0.1, and the relative error is less than 3.0%, which requires the radius of raindrops in 20 ℃ still air to be r<1.9×10-5 m for the Stokes formula to always hold true. It can be seen that the Stokes formula is completely unsuitable for raindrops of ordinary size. The article points out that the purpose of the article is to accurately calculate the terminal velocities of spherical model raindrops to make up for the shortcomings of some other literature, and the Wallis fitting formula used is relatively the most reliable. Related Articles | Metrics | Comments（0）

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Uncertainty principles based on Fourier Transform YU Hai-yan1, ZHENG Shen-zhou2 College Physics    2024, 43 (01): 1-.   DOI: 10.16854/j.cnki.1000-0712.230075 Abstract （439）      PDF（pc） （797KB）（406）       Knowledge map    Save Taking the square of normalized modulus for the wave function of quantum mechanics as the density function of probability, the Heisenberg inequality with positive lower bound for a product of the variance of displacement function and velocity function is described. It is proved by the derivative property of Fourier transform, Plancherel lemma and Cauchy-Schwarz inequality. Hardy uncertainty principle shows that an integrable function and its Fourier transform can not rapid attenuation at the same time. The Gauss function with a negative power is to achieve the best way for the Hardy uncertainty. We apply the Phragmen-Lindelof theorem (unbounded region on the maximum modulus principle) and the argument of complex analysis to prove the Hardy uncertainty principle. In addition, we also provide some generalizations of Hardy inequality, such as the Morgan inequality and the Beurling uncertainty principle. Related Articles | Metrics | Comments（0）

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Measurement of Young's modulus of metal wires using micro-resistance measurement TANG Jie-yang, LYU Mei-yu, WANG Yi-fan, YANG Jia-xu , ZHOU Liu-zhu College Physics    2024, 43 (02): 68-.   DOI: 10.16854 /j.cnki.1000-0712.230086 Abstract （437）      PDF（pc） （516KB）（709）       Knowledge map    Save An experimental device that can measure and display Young's modulus of metal wire online in real time was designed, based on the principle of tiny resistance measurement and based on the relationship equation between the modulus of elasticity and the amount of tiny change in the resistance of metal wire. When the metal wire is stretched and causes a small change in resistance, the magnitude of Young's modulus can be displayed in real time on the display after being amplified by a two-stage integrated operational amplifier circuit, analog/digital conversion, microcontroller acquisition and calculation. The data measured on a 0.201mm diameter steel wire and a 0.269mm diameter constantan wire show that the Young's modulus of the wire measured by this device has a relative error of no more than 0.3%, high accuracy, simple operation and short measurement time, and provides a feasible method for rapid measurement of the Young's modulus of the wire. Related Articles | Metrics | Comments（0）

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Design and research of impedance transformer based  on rectangular waveguide HUANG Yong, ZHAO Teng, WANG Xiu-fang College Physics    2024, 43 (01): 57-.   DOI: 10.16854 /j.cnki.1000-0712.230010 Abstract （422）      PDF（pc） （874KB）（467）       Knowledge map    Save Impedance mismatch is an important problem in the design of microwave RF circuits, which affects the size of power transmission and can cause microwave circuits to fail to work properly when severe. In order to eliminate reflections and improve the transmission efficiency of power, it is necessary to insert a matching network between microwave components to achieve impedance matching. The main study in this paper is an impedance matching network that matches pure resistive loads, called impedance transformer. In this paper, we propose to design a stepwise impedance transformer for a rectangular waveguide directional coupler with a coupling degree of C of about 30 dB, a directionality D ≥ of 20 dB, S11 <-20 dB, a frequency bandwidth of ± 0.2 GHz and a center frequency of 5.8 GHz, so that it matches the BJ70 interface. Three impedance transformer, namely one-quarter wavelength impedance transformer, binomial impedance transformer and Chebyshev impedance transformer, were designed and studied. Summarizing the applicable occasions of the three types of impedance transformer, the comprehensive index of the quarter-wavelength impedance transformer is best obtained by comparison, which is most suitable for the matching network of the directional coupler designed in this paper. Related Articles | Metrics | Comments（0）

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Discussion on the experimental principle of sound velocity measurement SU De-zhi, ZHANG Ji-lei, SUN Xiao-wei, DUAN Jin-peng, MA Shuai-qi College Physics    2024, 43 (01): 16-.   DOI: 10.16854/j.cnki.1000-0712.230031 Abstract （421）      PDF（pc） （1113KB）（1752）       Knowledge map    Save Aiming at the problem that the theoretical derivation of the change of sound pressure at the receiving end in the sound velocity measurement experiment is not perfect, especially the unclear explanation of the principle for the phase comparison method, a multiple reflection model based on sound pressure equation is established from the relationship between the amplitude and the sound pressure. In the model the plane simple harmonic wave function, the formula of sound pressure reflection coefficient and the principle of wave superposition are used to derive the formula of the change of the amplitude and phase of sound pressure at the receiver with distance, and the principle of the standing wave method and the phase comparison method are explained. The simulation results show that the amplitude and phase of sound pressure at the receiver are not strictly periodic functions, and the measurement accuracy is related to factors such as the sound absorption coefficient and the sound pressure reflection coefficient. Finally, the experimental verification is carried out, and the experimental measurement results are in good agreement with the calculation results of this model. This study provides theoretical guidance for correctly understanding the physical nature of the experiment. Related Articles | Metrics | Comments（0）

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Testing and assessment of calculus-based Newtonian mechanics  teaching and learning XU Ming-jiao, FENG Fu-yang, CHEN Lan-xin, ZHANG Mei College Physics    2023, 42 (12): 1-.   DOI: 10.16854 /j.cnki.1000-0712.230164 Abstract （395）      PDF（pc） （876KB）（489）       Knowledge map    Save Most college students have difficulties in learning physics.In order to improve the quality of teaching，this paper starts with the analysis of test scores of Newtonian mechanics as part of the course—Fundamental Physics using SPSS software.The test scores come from two exams: one is Force Concept Inventory，and the other is the teacher's selfdesigned calculus-based Newtonian mechanics quiz.Descriptive statistics，normality test，difference test and correlation analysis were carried out on the scores of Class 06 of the course in Grade 2022 students at Beijing Normal University.Based on the analysis of specific test questions，it is concluded that students are easily confused with related knowledge，poor in the application of theoretical knowledge in physical situations，and low in the mastery of mathematical tools such as calculus.In view of the above problems，some teaching suggestions are put forward. Related Articles | Metrics | Comments（0）

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A review of the development of d-band center theory to study the  mechanism of MoS2 electrocatalytic hydrogen reaction LIU Shi-ping, HUANG Xiao-xiao College Physics    2024, 43 (02): 71-.   DOI: 10.16854/j.cnki.1000-0712. 230220 Abstract （375）      PDF（pc） （674KB）（463）       Knowledge map    Save Molybdenum disulfide (MoS2) nanosheets, a typical two-dimensional material,have received much attention for its unique tunable electronic structure and excellent electrocatalytic activity for hydrogen evolution reaction (HER). In order to further improve its electrocatalytic performance,in-depth investigations on microscopic HER mechanism have been conducted to elucidate the key factors influencing the electrocatalytic performance within the material's electronic structure and construct reasonable electronic descriptors. This paper reviews the origin,development and current status of the d-band center theory to probe the mechanism of MoS2 electrocatalytic HER in recent years,with a view to providing guidance for the further development of this type of catalyst. Related Articles | Metrics | Comments（0）

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Study on the effect of wave packet incidence on resonance penetration phenomenon DENG Zhi-jiao, LI Mao-yuan, SHEN Yong, LIU Wei-tao, CHEN Ping-xing College Physics    2024, 43 (3): 1-.   DOI: 10.16854/j.cnki.1000-0712.230202 Abstract （368）      PDF（pc） （801KB）（454）       Knowledge map    Save Resonance penetration is an important phenomenon in one-dimensional quantum scattering. In general textbooks, the explanation of this phenomenon assumes monochromatic plane wave incidence, and there is a lack of research on wave packet incidence which is closer to the actual situation. In this paper, the main characteristics of wave packet scattering in one-dimensional square well and the influence of the mean and broadening of incident wave packet’s energy on resonance penetration are discussed in detail by means of analytical derivation and drawing. The research content of this paper can not only deepen the understanding of resonance penetration phenomenon, but also provides a general method for the analysis of the scattering problem of arbitrary piecewise constant potential function. Related Articles | Metrics | Comments（0）

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Derivation ofthe De Broglie matter wave equation WANG Yang College Physics    2024, 43 (5): 22-.   DOI: 10.16854/j.cnki.1000-0712.230226 Abstract （354）      PDF（pc） （762KB）（435）       Knowledge map    Save 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. Related Articles | Metrics | Comments（0）

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College Physics    2024, 43 (02): 13-.   DOI: 10.16854/j.cnki.1000-0712.230033 Abstract （322）      PDF（pc） （521KB）（418）       Knowledge map    Save Related Articles | Metrics | Comments（0）

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Study on resonant tunneling conditions of a one-dimensional double  barrier single well model ZENG Jia-zhong1, ZENG Xiao-qi2 College Physics    2024, 43 (3): 5-.   DOI: 10.16854/j.cnki.1000-0712.230137 Abstract （319）      PDF（pc） （810KB）（280）       Knowledge map    Save For double-barrier or multi-barrier systems, resonant tunneling will occur when the incident particle energy conforms to the resonant energy level, making the transmittance a maximum. This important property has broad application prospects in many quantum or semiclassical devices. In this paper, we mainly study one-dimensional double square barrier model and ABABA double square barrier system with high symmetry. Based on the Schrodinger equation, a general method for calculating the transmissivity of one-dimensional double-barrier system is derived, which provides a reference formula for numerical calculation, and proves the existence of analytical solution of transmissivity. For the ABABA double square barrier system model with high symmetry, the analytical expression of transmissivity is derived, the analytical solution of resonant tunneling condition is given, and the necessary conditions and influencing factors of resonant tunneling are discussed. Related Articles | Metrics | Comments（0）

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Gravitoelectric field, gravitomagnetic field and gravitational wave HE Xiao-kai, CAO Zhou-jian College Physics    2023, 42 (12): 33-.   DOI: 10.16854/j.cnki.1000-0712.230128 Abstract （315）      PDF（pc） （837KB）（370）       Knowledge map    Save  In many textbooks, gravitational waves are described as perturbations of flat spacetime. Under the weak field approximation, gravitational interactions can be described in a similar form to the Maxwell equation, corresponding to the concepts of gravitational electricity and gravitational magnetism. The weak gravitational field naturally corresponds to the perturbation of flat spacetime. Due to the fact that gravitational waves, gravitational electricity, and gravitational magnetism can be described as perturbations of flat spacetime, it is interesting to ask the relationship between gravitational waves, gravitational electricity, and gravitational magnetism. The analysis in this article indicates that gravitational electricity and gravitational magnetism correspond to the behavior of the near region of the gravitational source, but cannot describe the wave behavior in the far region. That is to say, the gravitational electricity and gravitational magnetism commonly used in literature cannot describe the behavior of gravitational waves.  Related Articles | Metrics | Comments（0）

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The development of the Beijing Normal University Physics Tournament and its role in cultivating top innovative talents LI Jia-hong, LIANG Ying, MA Yu-han College Physics    2023, 42 (12): 37-.   DOI: 10.16854/j.cnki.1000-0712.230168 Abstract （305）      PDF（pc） （885KB）（612）       Knowledge map    Save Since its inception in 2010, the China Undergraduate Physics Tournament (CUPT) has gone through 13 years of development and is currently the most influential undergraduate physics competition in China, with nearly 200 universities participating annually. Beijing Normal University (BNU) was one of the earliest universities to participate in CUPT and launched its own campus-level physics academic competition (BNUPT) in 2011. This paper provides a systematic review of the development of the PT series competitions at BNU and their role in cultivating top innovative talents in the physics department. Based on this, possible future development directions for the PT series competitions at BNU are proposed, including: 1) moving from intra-campus to inter-campus exchanges; 2) utilizing social media platforms to promote and exchange information on optimizing competition models, addressing competition topics, and related teaching research; 3) combining BNUs talent cultivation philosophy in research-oriented teachers to build an innovation talent cultivation bridge between university and high school stages based on the Physics Tournament (PT) model and practicing and promoting the PT educational model in basic education. Related Articles | Metrics | Comments（0）

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How to build a heat engine between two black holes: Starting  from the 2023 CPhO problems MA Yu-han College Physics    2024, 43 (02): 27-.   DOI: 10.16854/j.cnki.1000-0712.230398 Abstract （305）      PDF（pc） （580KB）（338）       Knowledge map    Save The theoretical fifth problem in the final round of the 2023 Chinese Physics Olympiad (CPhO) involves black hole thermodynamics. In this paper, we provide an introduction to the background of black hole thermodynamics and further analyze the characteristics of thermodynamic cycles between black holes based on our research experience. Finally, we summarize some recent research progress in the field of finite system thermodynamics and statistical physics relevant to this topic. Related Articles | Metrics | Comments（0）