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1、电磁学 (Electromagnetism)The combination of electrical and magnetic phenomenaElectric Charge and Electric Field1. Static Electricity2. Electric Charge and Its Conservation3. Insulators and Conductors4. Induced Charge5. Coulombs LawNew Words and Expressionsstatic charge 静电荷 quantized 量子化的 elementary cha
2、rge 基本电荷 conductor 导体 insulator 绝缘体 induce 感应 Coulomb 库仑 point charge 点电荷 permittivity of free space 真空电容率 electric field 静电场 test charge 试验电荷(a) Rub a plastic ruler (b) bring it close to some tiny pieces of paper.Electric Charge and Its Conservation Insulators and conductors Induced Charge1 Static
3、electricity1. Electric charge (电荷)It is an intrinsic character of the fundamental particles making up those objects.Charges with the same sign repel each other and charges with opposite signs attract each other. That is: unlike charges attract, like charges repel Charge is an intrinsic property of m
4、atter. Two types: Positive Charge: Protons Negative Charge: ElectronsThe net amount of electric charge produced in any process is zero. 3. The SI unit of charge is the CoulombThe SI unit of charge is the coulomb (C). 2. Law of conservation of electric charge4. Electric charge is quantizedq=n|e| , wh
5、ere n is a positive or negative integer, and e is a constant of nature called the elementary charge (基本电荷). 1|e|=1.6010-19C. 物体带电量都是基本电荷的整数倍。电荷的这种特 性叫电荷的量子性(quantized)。1)All the electrons/protons have identical electric charge.2) All the electric charges of charged body are integral times of that of
6、 an electron/proton.The charge of an electron is:The charge of a proton is:Unit C is the abbreviation of Coulomb1 C of charge is equal to the magnitude of the charge ofelectrons.Conductors are materials in which some of negative charge can move freely. 5. Conductors and Insulatorsnonconductors（insul
7、ators） semiconductorssuperconductorsConductors and InsulatorsConductors and Insulators（导体和绝缘体（导体和绝缘体 ）Most things are in between perfect conductor / insulator22Electrons are free to move in a perfect conductor.Electrons stay with their atom in an perfect insulator.Semiconductors (半导体)6. The methods
8、to get electric charges1) Charged due to rubbing (摩擦起电)(a) Rub a plastic ruler and(b) bring it close to some tiny pieces of paper.2) Induced Charge (感应起电) A positively charged object is brought close to a neutral metal rod.Neutral metal rodmetal rod still neutral, but with a separation of chargeChar
9、ges move and leave a positive charge at the opposite end.It is said to be induced (感应).Coulombs Law1. Point charge (点电荷)当带电体的线度与它到其它带电体之间距离或到研究点之间的距离相比足够小时(dr), 可忽略其大小,将电荷看成集中于一点的带电体，称点电荷. The sizes of objects are much more smaller than the distance between them. With the torsion balance (扭称实验)Coulo
10、mb established the Coulombs law of electrostatic interaction: 2. Coulombs LawThe force between two point charges at rest was inversely proportional to the square of the distance between them and proportional to the product of the charges. SI制 k is a proportionality constant. （ 为真空电容率 permittivity of
11、 free space ）令Direction ：The direction of the electric force is always along the line joining the two objects. If the two charges have the same sign, the force on either object is directed away from the other. If the two charges have opposite signs, the force on one is directed toward the other. (1)
12、 It is an exp. Law, holds both for macroscopic & microscopic, only holds for “point charge” model.(2) There are four basic physical quantities for electromagnetic quantity in the SI system. They are length (m), mass(kg), time(s), current(A). (3) principle of superposition. The net force on any one o
13、f them will be the vector sum of the forces due to each of the others.Vector sumDescription:Example :The electron and proton of a hydrogen atom are separated (on the average) by a distance of about 5.3x10-11 m. Find the magnitude of the electric force that each particle exerts on the other. q1 =-1.60x10-19 C, q2 =1.60x10-19 C, r = 5.3x10-11 mFrom Coulombs lawSolution :Thank you!Thank you!
