Table of Content

20 October 2019 Volume 38 Issue 10

  

Teaching control theory in physics: the port-Hamiltonian framework

LIU Chang

College Physics. 2019, 38(10):  1.  doi:10.16854 /j.cnki.1000-0712.180691

Abstract ( 3140 )   PDF (1056KB) ( 1197 )  

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The control theory has wide application and is also important in physics teaching. Based on the formalism of Hamiltonian mechanics，the port-Hamiltonian framework provides a physics-based control strategy. This framework is also promising in teaching control theory in physics. In this paper，we employ the port - Hamiltonian framework to reformulate some classical physics systems and introduce the resulting physics - based control strategies，including the energy，dissipation and structure assignments. The closed-loop Hamiltonian is thus a candidate of Lyapunov function，which achieves the ( asymptotic) stability. The introduced physics-based control strategies are demonstrated using the Duffing oscillator and the Lorenz system. We also provide port-Hamiltonian descriptions for two examples in celestial mechanics.

Research on two-dimensional standing waves on right-angled thin sector plate with two simply-supported radial edges

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

College Physics. 2019, 38(10):  8.  doi:10.16854 /j.cnki.1000-0712.190006

Abstract ( 1304 )   PDF (670KB) ( 335 )  

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Under small flexivity theory，the vertical small vibrations on right-angled sectorial thin plate which placed horizontally with two simply-supported radial edges and cantilevered arc edge is investigated theoretically and experimentally. The normal modes of analytical solutions on thin plate in different eigen frequencies are studied，and the radii of arc-shaped standing waves nodes on the plate are calculated. Furthermore，the laws of equation's eigen - values and the modulus of plate are obtained，and the patterns of standing waves are also observed. Three kinds of standing waves nodes on a metal board are presented: only having radical nodes，only having arc-shaped nodes ( two radial edges excluded) ，and both having radical nodes and arc-shaped nodes. The theoretical values coincide with the experimental results.

Understanding the half wave loss from the perspective of unitary transformation

DENG Zhi-jiao, YANG Kai-wei

College Physics. 2019, 38(10):  15.  doi:10.16854 /j.cnki.1000-0712.180642

Abstract ( 1828 )   PDF (279KB) ( 502 )  

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For both mechanical wave and optical wave，the half wave loss might happen in the reflected wave at the interface of different media. The half wave loss and energy conservation can be inferred from the solution of wave functions. In this paper，we take the mechanical wave as an example to give the insights of the essential conditions of the half wave loss and its necessary connection with energy conservation from the perspective of unitary transformation.

Multiple image method for the electrical field of the three charged metal spheres

LI Xin, JIAO Teng-fei, SUN Min, XIAO Chuan-yun, HUANG De-cai

College Physics. 2019, 38(10):  18.  doi:10.16854 /j.cnki.1000-0712.180702

Abstract ( 1379 )   PDF (1233KB) ( 641 )  

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The image method is a basic method to solve electrostatic field. This paper has used capacitance and charge methods to obtain multiple image charges of a system of three metal spheres. The distribution of electrostatic field is calculated by the effective and image charges. The numerical results confirm the consistence of the derived analytic results. The transition from attractive to repulsive interaction between two metal spheres can be realized by modulating the position and charged quantity of third metal sphere. By using Matlab software，the distribution of electric potential is directly compared for the system of two and three metal spheres.

Theoretical analysis and discussion on magnetic field of current-carrying coil and finite-length straight solenoid

CHEN Xue-wen, WU Lian, ZHANG Jia-wei, WU Ting, XIE Teng-hui

College Physics. 2019, 38(10):  23.  doi:10.16854 /j.cnki.1000-0712.180670

Abstract ( 1863 )   PDF (906KB) ( 786 )  

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The integral expression of magnetic induction distribution by a single current-carrying circular coil at any point is analyzed through Biot-Savart law. The analytical results are obtained and the distribution of magnetic induction lines are described by using Mathematic. The characteristics of magnetic induction distribution on the circular surface，where the current-carrying circular coil is located，are also analyzed. Besides，the magnetic induction distribution of long straight solenoid at any point is discussed by the results of current-carrying circular coil. The“uniform region”of magnetic field distribution is discussed and analyzed by numerical calculation. The distribution of magnetic induction line is described by Mathematica. Finally，the problems related to College Physics and College Physics Experiments are discussed.

Discussion on spin being angular momentum

CHENG Jian-jian, ZHENG Hua

College Physics. 2019, 38(10):  28.  doi:10.16854 /j.cnki.1000-0712.190119

Abstract ( 1644 )   PDF (146KB) ( 572 )  

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Only taking into account the results measured in Stern -Gerlach experiment，we obtain that the commutator relations of spin operators are similar to the ones of orbital angular momentum operators by using the rule of taking trace of matrix without introducing the matrix representation of spin operator. Then we conclude that the spin and orbital angular momentum belong to the same kind: angular momentum，which is different from the original concept of spin introduced in history and the one in quantum mechanics textbooks. We attempt to discuss about that the spin belongs to angular momentum with the philosophy“birds of a feather flock together”.

Interference patterns of independent point line plane wave function in momentum space

ZHAO Jun-ya, WU Jian-qing, MA Xiao-dong

College Physics. 2019, 38(10):  30.  doi:10.16854 /j.cnki.1000-0712.180547

Abstract ( 1136 )   PDF (927KB) ( 231 )  

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In the configurational space，there is no inference pattern formed by independent point，line segment， square-like and their array wave functions because there is no overlap between different parts of them. However， in the momentum space，the inference patterns can be constructed respectively. Results show that，along with the increase of the independent parts，the interference pattern tends to be localized with some fine structures in it. Studies of these inference pattern can be helpful to understand quantum mechanics.

A design for comprehensive experiments of grating diffraction and biprism experiments based on spectrometer

HUANG Wei, TANG Zhao-jun, ZHOU Xiao-hu, JIA Xin-yan, FAN Dai-he

College Physics. 2019, 38(10):  37.  doi:10.16854 /j.cnki.1000-0712.190053

Abstract ( 1212 )   PDF (648KB) ( 348 )  

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Currently，the experiments of adjusting and using of spectrometer，grating diffraction and biprism interference are the items carried on in most of the universities in China. Besides，these three experiments are also the contents of the national high school physics competition. In this paper，by integrating these three experiments，a comprehensive experiment of measuring the grating and the biprism parameters based on spectrometer is proposed. This experiment can realize the measurements of physical parameters，such as biprism wedge angle，refractive index，and grating constant. Furthermore，its feasibility is also analyzed. The proposed scheme should strengthen students' ability to use the optical instruments and also can be used as a set of experimental skills of testing program to the high school students who planed to participate in the national middle school physics competition.

Theory modification of the weak vibration in double grating

ZHAI Li-peng, LIU Ping, CHENG Lin, ZHANG Jun-wu, CHANG Kai-ge, TONG Tong, WANG Xue-dong

College Physics. 2019, 38(10):  41.  doi:10.16854 /j.cnki.1000-0712.180673

Abstract ( 2314 )   PDF (1334KB) ( 1036 )  

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In this paper，the formation of the optical beat in double grating diffraction and the related principle of weak vibration measurement are presented. By comparing the simulation results with the experimental results，a modification of the optical signal expression is established. It is found that the vibration of the grating induces the vibration of the diffraction spots and causes the modification. In addition，the mechanism of the burr signal caused by the senior diffraction of the grating is revealed and the suppression methods are studied. One of the methods is to make two gratings as parallel as possible，while the other method is to suppress senior diffractions by reducing the intensity of light source properly.

Measuring soap bubble thickness with color simulationand Match

LI Cheng-jin, QIAN Zheng, DING Yun, HUANG Zhen-yu, LU Xiao-yu, XU Fu-liang

College Physics. 2019, 38(10):  47.  doi:10.16854 /j.cnki.1000-0712.1900043

Abstract ( 1793 )   PDF (1133KB) ( 1098 )  

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The soap bubble often appears in daily life and physics. Particularly，it is mentioned when to introduce thin film interference as an example. Peoplewonderwhatisthickness of various soap bubbles. Inthispaper， theinterferencepatternsonthesurfaceof soap bubblesareobserved and photographed. With simulation of the light spectrums of LED's ray and the spectral sensitivity functions of the camera，the thickness of soap bubble is measured with color-matching. Finally，it is pointed that monochromatic light for this experiment is more advantage to white light.

Advances of prevention and control mechanism and the application of the modern physical technology in IPM plant protection engineering

LI Yu-ping, GONG Ning

College Physics. 2019, 38(10):  52.  doi:10.16854 /j.cnki.1000-0712.190076

Abstract ( 1197 )   PDF (465KB) ( 296 )  

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Physical control breaks through the traditional concept of crop pest control and agricultural production mode，and reduces the use of chemical pesticides. Physical control is an important measure to ensure food security and to improve the quality of agricultural products. It is of great significance to the healthy cycle of the ecological environment. In this paper，the mechanism of controlling diseases and insect pests by physical plant protection techniques，such as light，electricity，magnetism and sound，is introduced. The application of these modern physical technologies，such as light，electricity，magnetism，sound and temperature，in the integrated control of crop diseases and insect pests is reviewed. The shortcomings of physical prevention and control are analyzed. The application prospect of the modern physical plant protection technology in pest control is prospected. Some constructive suggestions are put forward in order to provide a reference for the research and application of IPM and realize the sustainable development of agriculture.

Study of spatial broadening and chirp of ultrashort laser pulses

CAO Yu-xiang, LI Qin, YAN Xiao-na, DAI Ye

College Physics. 2019, 38(10):  61.  doi:10.16854 /j.cnki.1000-0712. 180689

Abstract ( 1409 )   PDF (1207KB) ( 426 )  

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Spatial broadening of ultrashort laser pulses with a certain spectral width is studied after passing through a pair of parallel gratings. Firstly，the formulas for calculating the spatial broadening of ultrashort laser pulses after passing through a pair of gratings are derived by using the conventional grating equation and geometric optics knowledge. The experimental results also show that with an increase of the distance between grating pair，the transverse axis length of the pulsed spot increases and fits very well with the theoretical value. Finally，the spatial spectral distribution of the broadened pulsed spot is measured point by point by a fiber spectrometer，and the result verifies appearance of the spatial chirp characteristics.