Table of Content

04 May 2023 Volume 42 Issue 4

  

Questions and reflections on Rabi’s signal theory

CHEN Pei-feng, RUAN Jun-hui

College Physics. 2023, 42(4):  1.  doi:10.16854 /j.cnki.1000-0712.220218

Abstract ( 248 )   PDF (244KB) ( 142 )  

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Rabi strong signal theory is a very important theory in the interaction between laser and atom. In the teaching process, through the analysis of the questions raised by the students, this paper finds that the results of the Rabi strong signal theory are closely related to the initial conditions of atoms, and further analyses the importance of phase in quantum mechanics. 



X-ray diffraction and reciprocal lattice

HUANG Bing-xin, QIANG Wen-jiang

College Physics. 2023, 42(4):  4.  doi:10.16854 /j.cnki.1000-0712.220329

Abstract ( 498 )   PDF (1119KB) ( 409 )  

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The abstract concepts of X-ray diffraction and reciprocal lattice are difficult to learn.The theoretical basis of X-ray diffraction analysis is reciprocal lattice，and the construction of reciprocal lattice is based on X-ray diffraction.The two concepts are based on each other.However，X-ray diffraction and reciprocal lattice are explained separately in most textbooks，which brings difficulties for learning and understanding.In this paper，the principle of X-ray diffraction is introduced systematically.Then the reciprocal lattice based on X-ray diffraction，X-ray diffraction and reciprocal lattice are explained in a unified way in order to make learning and understanding easier.


Schrödinger equation introduced by using Noether^,s  theorem and Taylor^,s expansion

YANG Xiao-ning, WANG Feng, LI Jun-gang

College Physics. 2023, 42(4):  13.  doi:10.16854/j.cnki.1000-0712. 220257

Abstract ( 313 )   PDF (200KB) ( 244 )  

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In quantum mechanics, Schrödinger equation is used to describe how the motion of microscopic particles changes with time, and its significance is self-evident. In traditional teaching, Schrödinger equation is usually introduced directly as a definition, or gradually guided and established by the wave-particle duality of experimental facts. However, the traditional guidance and construction methods have certain leaps, their logic is not rigorous, and they lack deep-seated principle support, which is not conducive to the in-depth understanding of some students. The purpose of this paper is to start from the deep-seated theoretical framework of symmetry and one-to-one correspondence of conservation quantities, carries out mathematical derivation on the basis of Taylor^,s expansion, and gradually introduces Schrödinger equation on the basis of students^, quantum mechanics and mathematical knowledge. Firstly, we introduce the traditional introduction methods. Secondly, on the basis of reviewing Taylor^,s expansion, we introduce Taylor^,s translation concept, which forms an organic combination of old and new knowledge and further stimulates students^, creative thinking. Finally, the Schrödinger equation is naturally derived by using the concept of Taylor^,s translation and Noether^,s theorem.



Spectral interference and its application in thickness measurement of non-transparent samples

YANG Yong-jia, ZHANG Wei, QIN Zhen-zhen, CHEN Hao, ZHOU Zi-gang

College Physics. 2023, 42(4):  17.  doi:10.16854/j.cnki.1000-0712.220251

Abstract ( 246 )   PDF (428KB) ( 147 )  

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In order to in-situ acquire the thickness of non-transparent samples, such as metal strip, with high precision, a compact thickness measurement method of non-transparent samples with all fiber based on differential spectral interference has been proposed. Firstly, the basic principle of spectral interference and the specific implementation of absolute distance measurement are introduced. Then, a set of optical fiber differential spectral interference for non transparent sample thickness measurement is designed and built, and the principle verification experiment is carried out to realize the high-precision thickness measurement of standard gauge block. Finally, the measurement error of this method is analyzed, and the results show that the accuracy of this method can reach the sub micron level.



temperature and strain sensor

ZHANG Gang, GE Qiang, WANG Hui-sheng, WU Xu-qiang, YU Ben-li

College Physics. 2023, 42(4):  21.  doi:10.16854/j.cnki.1000-0712.220203

Abstract ( 390 )   PDF (760KB) ( 349 )  

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In order to achieve simultaneous temperature and strain measurement, in this paper, a fiber optic temperature and strain sensor based on multi-mode interference is proposed. The sensor is fabricated by splicing a section of thin polarization maintaining fiber and a piece of thin core fiber in a Sagnac loop with a fiber fusion splicer. Interference between polarization modes and core mode-high cladding modes exist in the sensor due to fiber offset and mode field diameter mismatch. The transmission spectra corresponding to the two types of interferences under different temperatures and strains are extracted by a low pass filter. The simultaneous temperature and strain measurement are validated by building a matrix through the temperature and strain sensitivities of two selected dips in transmission spectra. Experimental results show that the temperature and strain resolutions are 0.30 ℃ and 13.50 με, respectively. This experiment can be used as an innovative physics experiment for undergraduates majoring in physics and optoelectronics to help them master the principles of optical fiber sensing, experimental skills, and data processing and analysis methods.




Using the variable separation method to solve axisymmetric  magnetic field in equilibrium states

GUO Shi-yu, WU Wan-yun, YU Cong

College Physics. 2023, 42(4):  28.  doi:10.16854 /j.cnki.1000-0712.220379

Abstract ( 252 )   PDF (454KB) ( 241 )  

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The axisymmetric magnetic field configurations can usually be solved by  the variable separation method. Even for the more complex magnetic field configurations, such as the field with current source term, the variable separation method can also get satisfactory results. In this paper, we explain the orthogonal relationship between the magnetic potential function and the stream function. By using the variable separation method, we get axisymmetric magnetic field of the solar corona (with two magnetic flux ropes within the corona) in equilibrium states under the force-free condition. We numerically visualize the correspoding stream function solution. Finally, we conclude the feasibility of the variable separation method to solve the complex axisymmetric equilibrium magnetic field.






Measurement of air viscosity using double cylindrical resonators

DENG Yi-jing, FAN Jun, CUI Yue, LUO Ying-ying, JIN Long-xin, CHEN Yi-hang

College Physics. 2023, 42(4):  34.  doi:10.16854 /j.cnki.1000-0712.220195

Abstract ( 231 )   PDF (404KB) ( 122 )  

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The propagation characteristics of sound waves in a closed cavity depends on viscosity of air. Based on acoustic perturbation theory, the air viscosity can be demonstrated to be measured by sonic interference using double cylindrical resonators. Electric signal, generated by sweep signal generator, is converted into acoustic signal through a speaker. The acoustic wave is reflected back and forth in the cavity to form a standing wave. The acoustic-electric conversion is performed by a microphone and then, the electric signal is input into frequency sweeper. Using a frequency sweeper, the actual resonance frequency of air can be measured and compared with theoretical resonance frequency. It also can be used to calculate the air viscosity. The air viscosity at 24.5℃ is measured to be 178×10-5pa·s, and the relative error is 2.94% when compared with the recognized value. In order to explore the effect of temperature on the air viscosity coefficient, the air viscosity coefficient at different temperature is carried out. The results show that the air viscosity coefficient increases with increasing temperature.



Influence of geometrical parameters of water bottle with a neck on its vocalization frequency

SHI Zhao-long, LV Wei, MA Hao-ran, LIU Hong-yu, WU Jian-guang, ZOU Yong

College Physics. 2023, 42(4):  39. 

Abstract ( 195 )   PDF (484KB) ( 77 )  

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Aiming at the vocalization phenomenon of a bottle with a neck in the process of water injection, the influence of geometrical parameters of the bottle on its vocalization frequency is investigated. The container in the experiment is equivalent to Helmholtz resonance cavity. The relationship between the frequency and the geometric parameters of the water bottle with a neck is obtained by using Helmholtz resonance system theory and verified by experiments. In the experiment, Adobe Audition CS6 is used to sample the recorded sound. The influence of the change of geometric parameters on the sound frequency is explored by controlling the variables. The obtained data is sorted out and analyzed. The experimental results show that the shorter the neck length of the bottle and the larger the cervical cross-sectional area, the higher the sound frequency. The change of the shape has no effect on the sound frequency. The theory is in well agreement with the experiment and the sound phenomenon of bottle in the process of water injection can be well explained by Helmholtz resonance system.



Virtual experiment system of ammeter refitting based on Unity3D

WU Zhi-xuan, HOU Ze-xin, ZHANG Jun-jie, WU Wei, WANG Zeng-xu, LI Yong-tao

College Physics. 2023, 42(4):  44.  doi:10.16854 /j.cnki.1000-0712.220331

Abstract ( 285 )   PDF (486KB) ( 194 )  

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In order to facilitate the development of online physics experiment courses and further realize the computer examination of experimental operation, the virtual simulation experiment software of electricity meter refitting is designed and developed on Unity3D platform. The software can be used to adjust the circuit connection and all the actual controllable devices, thus to realize the complete simulation of the experiment process. The virtual instrument has the same appearance, operation steps and precision as the experimental instrument used in teaching. It is equipped with simple UI interface and can help students preview and review the principle and process of experiments on the computer. The design method and parameter selection basis of virtual instrument are described in detail.



Measure synchronization in coupled non-identical pendulums

PEI Wen-jie, WANG Xin-gang, ZHENG Hua

College Physics. 2023, 42(4):  51.  doi:10.16854/j.cnki.1000-0712.220254

Abstract ( 265 )   PDF (630KB) ( 94 )  

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 Synchronization is one of the most popular phenomena in nature, which is critical to our understanding on the behaviors of many complex systems. In this paper, we investigate numerically the influence factors, including the mass ratio between the beam and the pendulum, the mass difference as well as the length difference of the two coupled pendulums, to the occurrence of measure synchronization between two pendulums suspended from a common beam utilizing the MATLAB software. When the two coupled pendulums are identical, as the mass ratio R between the beam and the pendulum decreases, the interacting strength between the two pendulums will be increased. As R is decreased to be smaller than a threshold value, the two pendulums can achieve measure synchronization and their phase difference is kept fixed as π. When the mass difference or the length difference of the two pendulums is increased, the interacting strength of the two pendulums will be decreased and the pendulums will be desynchronized. 



The reproduction of rainbow and its polarization and interference

ZHANG Shu-wei, CHEN Qian, HUANG Zhao-cong, LI Jia-qi

College Physics. 2023, 42(4):  57.  doi:10.16854 /j.cnki.1000-0712.220336

Abstract ( 339 )   PDF (401KB) ( 279 )  

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One topic of 2021 CUPEC is “the design and reproduction of rainbow phenomenon”. In this paper, an experimental facility based on supercontinuum laser to reproduce rainbow is designed, which can give a good demonstration. Compared to reported rainbow experiments, the designed facility not only show rainbow phenomenon clearly, but also can be used to quantitatively analyze rainbow wave optics properties, including polarization and interference. This experiment is based on the common physical phenomena in daily life, but it is consistent with the wave optics of college physics. It can be as an interesting and exploratory physics experiment.



An rainbow reproduction and simulation superposition device in laboratory

YANG Zi-xuan, ZHANG Dan-xu, TONG Tong, GUO Yong-li, MAO Sheng-chun, WANG Xue-dong

College Physics. 2023, 42(4):  60.  doi:10.16854/j.cnki.1000-0712.220252

Abstract ( 193 )   PDF (503KB) ( 179 )  

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 Rainbow and neon are phenomena formed by sunlight refracting and reflecting in raindrops, which has important research significance. In this paper, solid homogeneous transparent balls with appropriate and equal diameter are used to replace water droplets, and multicolor light source is used to illuminate at an appropriate angle and distance to reproduce the phenomenon of rainbow and neon. On this basis, the experiments of reproducing rainbow phenomenon with single-ball and double-ball and realizing rainbow superposition with multi-ball are carried out respectively. The reproduced rainbow spectrum is measured by spectral analysis technology. The device designed in this paper integrates phenomenon demonstration and parameter measurement, and has important practical application value in optical experiment teaching and popular science education.