Journal Information
College Physics
Founded in 1982
Supervisor: China Association for Science and Technology (CAST)
Sponsor: China Physical Society
Bimonthly
Tel: 010-58808024
E-mail: cop@bnu.edu.cn
CN 11-1910/O4
ISSN 1000-0712
Current Issue
13 May 2024, Volume 43 Issue 3
  • Study on the effect of wave packet incidence on resonance penetration phenomenon
    DENG Zhi-jiao, LI Mao-yuan, SHEN Yong, LIU Wei-tao...
    2024, 43(3):  1.  doi:10.16854/j.cnki.1000-0712.230202
    Abstract ( 29 )   PDF (801KB) ( 35 )  
    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.

    Study on resonant tunneling conditions of a one-dimensional double  barrier single well model
    ZENG Jia-zhong1, ZENG Xiao-qi2
    2024, 43(3):  5.  doi:10.16854/j.cnki.1000-0712.230137
    Abstract ( 33 )   PDF (810KB) ( 22 )  
    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.


    Analytical application and generalization of an electrodynamics vector formula
    LIU Jian
    2024, 43(3):  11.  doi:10.16854/j.cnki.1000-0712.230110
    Abstract ( 34 )   PDF (699KB) ( 38 )  
     The research object of electrodynamics is the basic properties of the electromagnetic field, the law of motion of the electromagnetic field and the interaction between it and charged matter. This paper explores a common problem in electrodynamics: solving the bulk density of bound charges with known polarization strength, so that students will have difficulties in the situation, find new problems in the difficulties, and stimulate students, cognitive conflicts. In the teaching process, emphasis is placed on the application and transfer of knowledge and methods, arousing students, positive thinking, and cultivating students, scientific thinking and scientific inquiry abilities.

    Analysis of general methods for numerical solution of differential equations of motion
    JIA Xiao-wen
    2024, 43(3):  13. 
    Abstract ( 28 )   PDF (871KB) ( 29 )  
    The establishment process of differential equations of motion for physical models and the technical basis for numerical solution of the equations are analyzed. The numerical solution and analysis of the Saxon bowl, the spring pendulum in a magnetic field, and the three pendulum chaotic system are discussed. The general ideas and methods for solving the problem are given.

    Experimental design of sound source localization based on physical principle
    CHEN Xing-hui, YANG Yuan, DENG Jie, SU Dong-ye, CH...
    2024, 43(3):  20.  doi:10.16854 /j.cnki.1000-0712.230102
    Abstract ( 27 )   PDF (893KB) ( 16 )  
     An indoor sound source localization system is built by conventional physical experiment instruments, such as signal generator, DC regulated power supply, digital oscilloscope, DC motor, quad-microphone line array, digital display angle ruler, loudspeaker, and some self-made devices. The DC motor is used to drive the quad-microphone line array and the digital display angle ruler to rotate coaxially. The sound wave signal received by the quad-microphone line array is amplified and filtered and then sent to an oscilloscope. The sound is judged according to the shape of Lissajou figure on oscilloscope. For the source orientation, the rotation angle of the line array is measured by a digital display angle ruler, and then the position coordinates of the sound source are calculated by usin g trigonometric functions. Experimental results show that this method has high accuracy, small error and low cos t for sound source localization.

    The terminal velocities of spherical raindrops in still air and the usage conditions of Stokes viscous resistance
    SHAO Yun
    2024, 43(3):  25.  doi:10.16854/j.cnki.1000-0712.230210
    Abstract ( 36 )   PDF (847KB) ( 14 )  
    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.

    Exploratory study on tidal friction#br#
    XU Xiang-jing, CHEN Bo-yu
    2024, 43(3):  30.  doi:10.16854/j.cnki.1000-0712.230098
    Abstract ( 23 )   PDF (739KB) ( 15 )  
    This article investigates a simplified model of tidal locking in celestial binary systems. The central body is assumed to consist of a solid spherical core and a uniform liquid outer layer, and the deformation of the central body under gravity is approximated as ellipsoidal. The precision of this approximation is also demonstrated. Finally, the article uses the “constant geometric lag model” to calculate the tidal torque relative to the centroid of the central body when the central body has a deviation angle of θ from its equilibrium position. The conclusion is that the tidal frictional torque between the two celestial bodies is proportional to the square of the revolving body,s mass, the fifth power of the central body,s average radius, and inversely proportional to the sixth power of the distance between the two bodies.

    On the capacity of viscous fluid on rotating rod
    QIN Yi-xuan, GU Yi-lin, LUO Jia-li, XIA Cheng-jie,...
    2024, 43(3):  34.  doi:10.16854/j.cnki.1000-0712.230145
    Abstract ( 19 )   PDF (874KB) ( 17 )  
    By turning a rod covered with a viscous liquid (e.g.. honey), some of the liquid can be retained on the rod without dripping. For this phenomenon, most previous theories are based on the N-S equations, which cannot clearly explain the physical mechanisms of the phenomenon. In this paper, a simple theoretical model of the phenomenon dominated by viscous force, centrifugal force, gravity and surface tension is obtained through a simple force analysis and a method similar to dimensional analysis, which avoids the complex and lengthy solution of the hydrodynamic equations; Experimentally, self-consistent experimental data are obtained through the construction of a stable device and reasonable control of variables. The experimental results are in good contrast with the theory, and the physical mechanisms and key factors of the non-dripping of viscous liquid on the rotating rod are explained intuitively. The theoretical analysis is in good agreement with the experimental results, and the physical nature and key factors for the non-dripping of viscous liquids on rotating rods are explained intuitively.

    Study on floating phenomenon of metal disc on water surface
    ZHAO Dong-jing, DU Wang-yi-xin, WANG Jin-dong, ZHO...
    2024, 43(3):  39.  doi:10.16854 /j.cnki.1000-0712.230196
    Abstract ( 14 )   PDF (929KB) ( 15 )  
     In this paper, the phenomenon that a metal disk with a hole in the center can float on water surface is studied theoretically and experimentally. The turbulence model and the VOF model are established, and the critical
    Multiple questions and multiple solutions to one question of a motion-induced electromotive force problem
    GENG Fa-hao1, FAN Peng-dong2, ZHANG Meng2
    2024, 43(3):  45.  doi:10.16854/j.cnki.1000-0712.230181
    Abstract ( 39 )   PDF (852KB) ( 25 )  
    College physics is an important basic course of science and engineering. Engineering majors mainly teach basic mechanics and electromagnetism. Among them, the teaching of motion-induced electromotive force is the focus and difficulty of electromagnetics, and students make many mistakes in answering such questions. In this paper, the motion-induced electromotive force under translational cutting and rotational cutting is analyzed and calculated in detail by means of multiple questions and multiple solutions of typical examples of motion-generated electromotive force. In this way, students can deeply understand the physics and calculus knowledge points.

    Simulation and analysis of an improved magnetic field uniformity of solenoid
    ZHANG Xing-chi1, FEI Jun-hua2, LI Hui-xian2, WANG ...
    2024, 43(3):  51.  doi:10.16854/j.cnki.1000-0712.230090
    Abstract ( 21 )   PDF (823KB) ( 14 )  
    The magnetic field uniformity on the axis of a straight solenoid wounded tightly with multilayers is improved by adding compensation coils. According to theoretical formula and combined with Python software,the magnetic induction curve before and after adding compensation coils is simulated. Based on the simulation results,the variation law between the improved uniform interval size of the magnetic field and the compensation coil parameters,the simulation curve graph is further studied. It is found that when the number of turns of the compensation coil is determined,the uniform interval size will increase first and then decrease with the increase of current intensity,and it will suddenly rise and drop when the convex points enter and exit the threshold of the curve graph. Under the premise that the current intensity can be provided,the compensation coil with fewer turns can produce better extension effect on the uniformity of the primary magnetic field.

    Measurement of muon lifetime with oscilloscope
    HAO Jia-xin, GUO Ge, SUN Bao-hua
    2024, 43(3):  55.  doi:10.16854/j.cnki.1000-0712.230166
    Abstract ( 16 )   PDF (917KB) ( 12 )  
     Muon is the major cosmic rays at the sea level. It can be detected by scintillator detectors such as sodium iodide NaI(Tl). In paper, an experimental method is presented, which uses a high sampling rate oscilloscope to digitize the deposited signal of muon and the relevant decay signal, and the off-line analysis to determine the muon lifetimes. This experiment is relatively simple and can be extended as a frontier project for particle detection in college physics experiments, in which radioactive sources and conventional nuclear electronics are not essential. 

    Experimental measurement of the lifetime of cosmic ray  muon by plastic scintillation detector
    HE Wei-jie, LI Bo
    2024, 43(3):  60.  doi:10.16854/j.cnki.1000-0712.230197
    Abstract ( 17 )   PDF (1004KB) ( 5 )  
     In this experiment, a cosmic ray muon detector is designed based on plastic scintillator and photomultiplier with fast time response. The waveform of electrical pulse signal produced by charged particle in the detector is read out and recorded in computer by a digitizer. Through offline data analysis, the procedures of muon decay event selection, timing of pulse signal and lifetime fitting are completed. In this experiment, the rise time of pulse signal is less than 20 ns, and the noise is less than 3 mV. It is estimated that the time resolution of detector can reach an order of nano second by using leading-edge timing method. The measured average lifetime of the muon is 2.188±0.045 μs, which is consistent with the world average of muon lifetime with respect to the experimental error. 

    Simulation of the motions of celestial bodies based on Mathematica
    YU Jin-li, CONG Ya-xuan, LI Jia-yi, ZHOU Xing-yu, ...
    2024, 43(3):  67.  doi:10.16854 /j.cnki.1000-0712.230062
    Abstract ( 26 )   PDF (873KB) ( 28 )  
    Celestial motion is one of the basic contents of mechanics and theoretical mechanics. With the help of Mathematica software and based on relevant formulas and laws of classical mechanics, in this paper the motions of planets, periodic comets, and binary star systems are accurately and dynamically simulated. The vivid animations obtained in this study are very helpful for learners to establish clear physical images, increase their intuitive knowledge of planets, periodic comets, and binary star systems, and enhance their deep understanding of celestial motion laws. New physics teaching resources by visualizing the theoretical knowledge from textbooks by Mathematica programming is developed in this study. The tremendous potential of Mathematica software to develop physics teaching resources is also demonstrated.


    Concentration measurement of transparent liquid based on ultrasonic grating and temperature control system#br#
    LI Yi-tong1, CHEN Hang1, LI Cheng-qian1, DUAN Xue-...
    2024, 43(3):  74.  doi:10.16854 /j.cnki.1000-0712.230088
    Abstract ( 23 )   PDF (906KB) ( 15 )  
    Concentration is an important physical quantity to describe the properties of a solution. It changes with the change of temperature. Based on the method of ultrasonic grating measurement of sound velocity in transparent liquid, taking transparent sodium chloride solution as an example, the relationship among sound velocity, concentration and temperature is studied through the control variable method. Finally, the equations of these three parameters is obtained quantitatively, and the concentration is measured at different temperatures. The results show that the method has high confidence and small relative error, and is widely applicable to the measurement of transparent liquid concentration. It has the advantages of high timeliness, short response time and high precision.


    A dialogue about rainbow——Another face of a Physics Olympiad problem
    WANG Si-hui, ZHOU Hui-jun
    2024, 43(3):  79.  doi:10.16854/j.cnki.1000-0712.240025
    Abstract ( 28 )   PDF (947KB) ( 28 )  
     This paper reviews the history of rainbow theory, and discusses some possible problems in rainbow observation and experiment. Some methods for demonstrating rainbow and relevant the phenomena are presented.