《物理双语教学课件》Chapter-15-Electric-Fields-电场
Physics 15 Electric Charge
Electrons have a negative charge because of a historical choice rather than because of an intrinsic physical property.
In the presence of a charged object, a neutral object can polarize – the charges opposite to those on the charged object move closer to it, and the other charges move away.
15-2 Charge is Conserved and Quantized 1.Charge is conserved
Charge by friction Charge by Induction In observed reactions involving the so-called elementary particles, no one has ever seen a single case of net charge appearing or disappearing. Radioactive decay of nuclei The algebraic sum of all the electric charges in any closed system is constant.
Coulomb’s torsion balance
2. Coulomb’s law The electric force between charges q1 and q2 is (a) attractive if charges have opposite signs (b) repulsive if charges have same signs The magnitude F of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
大学物理-电磁学(英文授课)
大学物理-电磁学（英文授课）IntroductionElectromagnetism is a field of physics that concerns itself with the study of electromagnetic forces and fields. It is a branch of physics that focuses on the interaction between electrically charged particles, including charged particles at rest and moving charges. This course is designed to help students understand the basic principles of electromagnetism, including electric and magnetic fields, electromagnetic radiation, and electromagnetic waves.Electric FieldsElectric fields are created by electric charges, which are either positive or negative. The electric field is said to be the space surrounding a charged particle. If another charged particle is placed in the electric field, it will experience a force. The direction of the force depends on the charge of the particle and the direction of the electric field.Magnetic FieldsMagnetic fields are created by moving charges. A magnetic field is said to be the space surrounding a magnetic object. If a charged particle is placed in a magnetic field, it will move in a circular path. The direction of the circular path depends on the charge of the particle and the direction of the magnetic field. Electromagnetic FieldsAn electromagnetic field is created by the interaction of an electric field and a magnetic field. Electromagnetic fields have both electric and magnetic components, and they travel through space at the speed of light. Electromagnetic waves are a form of electromagnetic radiation that carries energy. Electromagnetic radiation includes radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays.Maxwell's EquationsMaxwell's equations describe the behavior of electric and magnetic fields. They are a set of partial differential equations that relate the electric and magnetic fields to the electric charges and currents that are present. The equations describe how an electric field can produce a magnetic field, and a magnetic field can produce an electric field. They also describe how the electromagnetic fields propagate through space.Electromagnetic WavesElectromagnetic waves are waves of energy that are propagated through space by the interaction of electric and magnetic fields. Electromagnetic waves do not require any medium to propagate through. They can travel through a vacuum, which is why they are also known as vacuum waves.Electromagnetic waves are classified based on their frequency and wavelength. Radio waves have the lowest frequency, and gamma rays have the highest frequency. Radio waves have the longest wavelength, and gamma rays have the shortest wavelength.Applications of ElectromagnetismElectromagnetism has many practical applications in our daily lives. Some of the most common applications include electric motors, generators, transformers, telecommunication devices, medical imaging devices, and microwave ovens. Electromagnetism has also played a significant role in the development of modern technology, including computers, television, radio, and mobile phones.ConclusionElectromagnetism is a fascinating field of physics that has wide-ranging applications in our daily lives. This course provides students with a comprehensive understanding of electric and magnetic fields, electromagnetic radiation, and electromagnetic waves. By studying electromagnetism, students can gain a deeper appreciation for the fundamental principles that govern the behavior of the universe around us.Electromagnetism is one of the four fundamental forces of nature, along with gravity, strong nuclear force, and weak nuclear force. It is a field of physics with numerous applications in our modern society. Without the understanding of electromagnetism, we would not have the modern comforts that we have today, including electricity, the internet, cell phones, and many other devices.One of the most significant contributions of electromagnetism to modern society is the use of electric motors. Electric motors are devices that convert electrical energy into mechanical energy.They are used in a wide range of applications, from household appliances to transportation systems. The underlying principle of electric motors is electromagnetic induction, which is the process of inducing an electric current in a conductor by varying the magnetic field around it.Another important application of electromagnetism is in generators. Generators are devices that convert mechanical energy into electrical energy. They are often used in power plants to generate electricity that is distributed to homes and businesses. The principle of electromagnetic induction is also used in generators. When a conductor moves through a magnetic field, an electric current is induced in the conductor.Electromagnetism also plays a central role in the functioning of transformers. A transformer is a device that changes the voltage of an alternating current (AC) power supply. Transformers are used to step up or step down the voltage of an AC power supply. They are used in power grids to maintain a constant voltage throughout the grid. The principle used in transformers is electromagnetic induction, with the primary and secondary coils of wire interacting with the magnetic field to produce the desired voltage change. Telecommunication devices, including radios, televisions, and cell phones, also rely on the principles of electromagnetism. The radio waves used for communication are a form of electromagnetic radiation. Radio waves are used to transmit and receive signals between devices. The workings of these devices depend on the principles of electromagnetic induction and electromagnetic radiation.In addition to powering devices, electromagnetism is used in medical imaging devices. Magnetic resonance imaging (MRI) machines use magnetic fields and radio waves to produce images of the body's internal structures. The patient is placed in a powerful magnetic field, which causes the protons in their body to align with the field. A radio wave is then sent through the body, causing the protons to produce a signal. The signal is detected, and an image is produced based on the strength and location of the signal.Microwave ovens are another example of electromagnetism in action. These appliances use microwaves to cook food. Microwaves are a type of electromagnetic radiation with a frequency of around 2.4 GHz. The microwaves cause the water molecules in the food to vibrate rapidly, producing heat. This heats the food quickly and evenly, making it a popular method for cooking.The study of electromagnetism has also led to the development of modern technology. Computers, televisions, radios, and cell phones all rely on the principles of electromagnetism. The development of these technologies has revolutionized the way we live and communicate. The internet, for example, would not exist without the principles of electromagnetism.In conclusion, electromagnetism is a fascinating field of physics with numerous practical applications in our daily lives. It is the foundation of modern technology, and our society would not be the same without it. By studying electromagnetism, we can gain a deeper understanding of the world around us and appreciate thefundamental principles that govern our universe. As technology advances, we can expect even more exciting and innovative applications of electromagnetism in the years to come.。
《电能与电功》电能与电功率PPT优质课件
D．消耗的电能为100J
课堂反馈
D 3、下列家用电器正常工作30min消耗电能最多的是（ ） A．电风扇 B．电脑 C．电视机 D．空调
课堂反馈
C 4、下列电学仪器中，能够直接测量电功的是（ ） A．验电器 B．电压表 C．电能表 D．电流表
课堂反馈
5、如图所示，是小英家上月初和上月末电能表的示数。结合表盘信息（其中imp 表示指示灯闪烁次数），下列
电子式多费率电能表
课堂反馈
1、如图所示的四种家用电器，工作时主要能量转化形式与其他 用电器不同的是（ C ）
A． 电熨斗
B． 电饭煲
C． 洗衣机
D． 电热水壶
课堂反馈
2、如图所示为电风扇能量流向图，根据该图提供的信息，下列说法不正确
的是（ ）
A
A．电流做功80J
B．（a）应为机械能
C．（b）的数值为20J
第十五章 电能与电功率
15.1 电能与电功
课前导入
现代社会生活和生产中几乎处处都离不开电。用电，实际上用的是电能。
遍布各地的电网
各种家用电器
电能的利用是如何实现的呢？接下来我们一起进行探究。
新知探究
一、电能与电功
电 能 的 获 得
火力发电
水力发电
化学能
水能 风能
核能
电能
太阳能
化学能
风力发电
核电
电池
电梯运行时 你还能想到哪些电能转化的事例？
电镀物品时
电能转化为 化学能
新知探究
一、电能与电功 活动1——了解“电功”
电能转化举例：
电脑运行时
电能转化为声能 、光能
电车运行时 电能转化为机械能
电热水壶烧水时 电能转化为内能
西尔斯当代大学物理双语PPT课件
.
17
轶事:蜘蛛织网和平面直角坐标系的创立
• 据说有一天，笛卡尔生病卧床，病情很重，尽管如 此他还反复思考一个问题：几何图形是直观的，而代数 方程是比较抽象的，能不能把几何图形和代数方程结合 起来？他苦苦思索，拼命琢磨，通过什么样的方法，才 能把“点”和“数”联系起来。突然，他看见屋顶角上 的一只蜘蛛，拉着丝垂了下来。一会功夫，蜘蛛又顺这 丝爬上去，在上边左右拉丝。蜘蛛的“表演”使笛卡尔 的思路豁然开朗。他想，可以把蜘蛛看作一个点。他在 屋子里可以上、下、左、右运动，能不能把蜘蛛的每一 个位置用一组数确定下来呢？他又想，屋子里相邻的两 面墙与地面交出了三条线，如果把地面上的墙角作为起 点，把交出来的三条线作为三根数轴，那么空间中任意 一点的位置就可以在这三根数轴上找到有顺序的三个数。 反过来，任意给一组三个有顺序的数也可以在空间中找 到一点P与之对应，这就是坐标系的雏形。
by describing how to calculate it from other quantities that we can measure.
speed = distance / time
v = d / t (m/s)
An equation must always be dimensionally consistent.
位移
average velocity
平均速度
instantaneous velocity
瞬时速度
acceleration
加速度
confusion
混淆
rectilinear motion
直线运动
.
20
valid
正确的
西尔斯当代大学物理双语PPT课件
.
10
1.6 Vector Algebra
a Vector quantity can be expressed by a
• Every physical theory has a range of validity. • No theory has ever regarded as the final truth.
1.2 Idealized Models A model is a simplified version of a physical
Chapter 1 Physical Quantities
and Vectors
.
1
1.1 The nature of physics
• Physics is an experimental science. • Physicists observe the phenomena of nature and try to find patterns and principles that relate these phenomena. These patterns are called physical theories or physical laws, or principles.
ball move in a vacuum.
We ignore the earth’s rotation.
point masses
We make the weight constant.
.
5
1.3 Standards and Units
Physics is an experimental science. Experiments require measurements.
【双语物理】静电场_1_electric field
F -The electric field������ is defined as: E lim , to qualify the strength of the field. q 0 0 q 0
-One charge creates a field which in turn acts on the other charge. -The normal component of the electric field exhibits discontinuity, with E crossing a boundary with surface charge density σ. Electric Field Lines 1. The field lines must begin on positive charges (or at infinity) and then terminate on negative charges (or at infinity). -Notice that the direction of field lines is radially outward for a positive charge and radially inward for a negative charge. 2. The direction of the electric field vectorat a point is tangent to the field lines. 3. The number of lines per unit area through a surface perpendicular to the line is devised to be proportional to the magnitude of the electric field in a given region. 4. The number of lines that originate from a positive charge or terminating on a negative charge must be proportional to the magnitude of the charge. 5. No two field lines can cross each other; otherwise the field would be pointing in two different directions at the same point.
双语物理课件.ppt
| r|
(x 2
x )2 1
(
y 2
y )2 1
(z 2
z )2 1
(ii). Different from the path (路程)
y
Displacement depends only on
r A
B the position of initial point and
r1(t)
r
r2(t+ t )
Relativity of description of motion (运动描述的相对性) Absoluteness of motion (运动的绝对性)
2-2. Position and Displacement (位置和位移）
1. Position Vector(位矢） The position vector extends from the origin of a coordinate system to the particle（从坐标原点到质点）.
2.
DΔisrplacre2mern1 t(位(移x2)——xΔ1)ir ( y2
y1 ) j (z2
z1 )k
Δ xi Δ yj Δ zk
(i). The magnitude of vector （矢量的量值） should be the
length of this vector （应为该矢量长度), i.e.
In rectangular coordinate system ( 直角坐标系 ) : r xi yj zk
Motion Function ( 运动方程 )：
r r(t)
y
P,
x(t)i y(t) j z(t)k
(t0) r(t)
大学物理：电磁学PPT
N F4
O
F2 B
en
M,N F1
O,P B
F2
en
l1 l1 M F1 sin F2 sin Il2 B l1 sin ISB sin 2 2 M IS B m B 线圈有N匝时 m NIS
2 电流元的磁场
dB
P *
I
Idl
0 Idl dB er 2 4 r
——毕奥-萨伐尔定律
r
3
磁场的叠加原理
B Bi
i
B dB
例 1： 判断下列各点磁感强度的方向和大小.
1 8 2Βιβλιοθήκη dB 0 1、 5 点 ：
7
Idl
R
6 5 4
例 5：
一半径为R，均匀带电Q的薄球壳。 求球壳内外任意点的电场强 度。
0 r R 如图，过P点做球面S1 E dS E dS 0 E 0
S1 S1
r
P
+ + +
+
S +1
O
如图，过P点做球面S2 rR E dS E dS Q / 0
rB
(electric potential )
点电荷电场 中的电势:
V
Q 40 r
电势的叠加 原理:
V Vi
i
点电荷电场中常取 无穷远处为电势零点
点电荷的电场线和等势面：
两平行带电平板的电场线和等势面：
+ + + + + + + + + + + +
《物理双语教学课件》Chapter14ElectricCharge电荷
《物理双语教学课件》Chapter14ElectricCharge电荷Chapter 14 Electric ChargeWe now begin a study of the branch of physics concerned with electric and magnetic phenomena. The laws of electricity and magnetism play central roles in operation of many devices such as radios, televisions, electric motors, computers, and high-energy accelerators. More fundamentally, we now know that the inter-atomic and inter-molecular forces that are responsible for the formation of solids and liquids are electric in origins. Furthermore, such forces as the pushes and pulls between objects and the elastic force in a spring arise from electric forces at the atomic level.The early Greek philosophers knew that if you rubbed a piece of amber, it would attract bits of straw. The Greeks also recorded the observation that some natura lly occurring “stone” known today as the mineral magnetite, would attract iron. From these modest origins, the sciences of electricity and magnetism developed separately for centuries-until 1820.The new science of electromagnetism,the combination of electrical and magnetic phenomena, was developed further by workers in many countries. One of the best was Michael Faraday, a truly gifted experimenter with a talent for physical intuition and visualization. In the mid-19th century, James Clerk Maxwellput Fa raday’s ideals into mathematical form, introduced many new ideas of his own, and put electromagnetism on a sound theoretical basis.14.1 Electric Charge1.The definition of electric charge: If you walk across a carpet in dry weather, you can produce a spark by bring your finger close to a metal doorknob. On a grander scale, lighting is familiar to everyone. Each of those phenomena represents a tiny glimpse of the vast amount of electric charge that is stored in the familiar objects that surround us. Electric charge is an intrinsic characteristic of the fundamental particles making up those objects.2.The classification of charge(1)The vast amount of charge in an everyday object is usually hidden because the object contains equal amounts of two kinds of charge: positive charge and negative charge. With such equality-or balance-of charge, the object is said to be electrically neutral; that is, it contains no net charge to interact with other objects.(2)If the two types of charge are not in balance, then there isa net charge that can interact with other objects. And webecome aware of the existence of the net charge. We say that an object is charged to indicate that it has a charge imbalance, or net charge. The imbalance is always very small compared to the total amount of positive charge and negative charge contained in the object.3.To see the demonstration ofthe figure, we come to theconclusion that charges withthe same electrical sign repeleach other, and charges with opposite signs attract each other.4.The SI unit of charge is derived from the SI unit of electric current, the ampere (A). The SI unit of charge is the coulomb (C).14.2 Conductors and Insulators1.In some materials, such as metals, tap water, and the humanbody, some of the negative charge can move rather freely. We call such materials conductors. In other materials, such as glass, chemically pure water, and plastic, none of the charge can move freely. We call these materials nonconductors or insulators.2.The properties of conductors and insulators are due to thestructure and electrical nature of atoms. Atoms consist of positively charged protons, negatively charged electrons, and electrically neutral neutrons. The protons and neutrons are packed tightly together in the central nucleus.3.The charge of a single electron and that of a single protonhave the same magnitude but are opposite in sign. Hence an electrically neutral atom contains equal numbers of electrons and protons. Electrons are held near the nucleus because they have the electrical sign opposite that of the protons in the nucleus and thus are attracted to the nucleus.4.When atoms of a conductor likecopper come together to form the solid,some of their outmost electrons do notremain attracted to the individualatoms but become free to wanderabout within the solid, leaving behind positively charged atoms. We call the mobile electrons conduction electrons. The experiment of the figure demonstrates the mobility of charge in a conductor.5.Semi-conductor, such as silicon and germanium, are materialsthat are intermediate between conductors and insulators. The microelectronic revolution that has changed our lives in so many ways is due to devices constructed of semi-conducting materials.6. Finally, there are superconductors , so called because they present no resistance to the movement of electric charge through them . When charge moves through a material, we say that an electric current exists in the materials. Ordinary materials, even good conductors, tend to resist the flow of charge through them, In a superconductor, however, the resistance is not just small; it is precisely zero .14.3 Coulomb ’s law1. Let two charged particles (also called point charges ) have charge magnitudes q 1 and q 2 and be separated by a distance r.(1) The electrostatic force of attraction or repulsion between them has the magnitude )'(412210221slaw Coulomb r q q r q q k F πε==,in which k is a constant with the value 229/1099.8C m N ??, called the electrostatic constant , and the quantity0ε, called the permittivity constant , with the value 2212/1085.8m N C ??-.(2) Each particle exerts a force of this magnitude on the other particle; the two forces form an action-reaction pair . If the particles repel each other, the forces on each particle point away from the other particle as in figures (a) and (b). If theparticles attract each other, the forceon each particle points toward theother particle as in figure (c).2.Coulomb’s law has the same form as that of Newton’sgravitational law.(1)Both describe inverse square laws that involve a propertyof the interacting particles-the mass in one case and the charge in the other.(2)The laws differ in that gravitational forces are alwaysattractive but electrostatic forces may be either attractive or repulsive, depending on the sign of the two charges. This difference arises from the fact that, although there is only one kind of mass, there are two kinds of charge.3.Coulomb’s law has survived every experimental test; noexceptions to it have ever been found. It holds even within the atom, correctly describing the force between the positively charged nucleus and each of the negatively charged electrons, even though classical Newtonian mechanics fails in that realm and is replaced there by quantum physics. This simple law also correctly accounts for the forces that bind atoms and molecules together to form solids and liquids.4. Still another parallel between the gravitational force and the electrostatic force is the both obey the principle of superposition . If we have n charged particles, they interact independently in pairs, and the force on any one of them, let us say particle 1, is given by the vector sum n F F F F F 11413121 ++++=, in which, for example, 14F is theforce acting on particle 1 owing to the presence of particle 4. An identical formula holds for the gravitational force.5. The two shell theorems that we found so useful in our study of gravitation have analogs in electrostatics: (1) A shell of uniform charge attracts or repels a charged particle that is out side the shell as if all the shell ’s charge were concentrated at its center. (2) A shell of uniform charge exerts no electrostatic force on a charged particle that is located inside the shell .6. Spherical conductors : If excess charge is placed on a spherical shell that is made of conducting material , the excess charge spreads uniformly over the external surface . This arrangement maximizes the distances between all pairs of the excess charge. According to the first shell theorem, the shell then will attract or repel an external charge as if the excess charge on the shell were concentrated at its center.14.4 Charge is quantized and conserved1.The experiment shows that electric charge is made up ofmultiples of a certain elementary charge. That is, any positive or negative charge q that can be detected can be written as = =nq, in which e, the elementary charge, has ±ne±,1±,3,2the value C19. The elementary charge is one of the .1-6010important constants of nature. The electron and proton both have a charge of magnitude e.2.When a physical quantity such as charge can have onlydiscrete values rather than any value, we say that the quantity is quantized. Energy, angular momentum are quantized; Charge adds one more important physical quantity to the list.3.If you rub a glass rod with silk, a positive charge appears onthe rod. Measurement shows that a negative charge of equal magnitude appears on the silk. This suggests that rubbing does not create charge but only transfers it from one body to another, upsetting the electrical neutrality of each body during the process. This hypothesis of conservation of charge has stood up under close examination, both for large-scale chargedbodies and for atoms, nuclei, and elementary particles. No exceptions have ever been found. Thus we add electric charge to our list of quantities-including energy and both linear and angular momentum-that obey a conservationlaw. We have a lot of examples: Radioactive decay of nuclei, annihilation process of electron and positron, and the pair production, the converse of annihilation.。
静电场(双语)
After knowing the divergence and the rotation of the electric
field intensity, one may write, with the aid of the Helmholtz’s
1. Field Intensity, Flux, and Field Lines 2. Equations for Electrostatic Fields in Free Space 3. Electric Potential and Equipotential Surfaces 4. Polarization of Dielectrics 5. Equations for Electrostatic Fields in Dielectric 6. Boundary Conditions for Dielectric Interfaces分界面 7. Boundary Conditions for Dielectric-conductor Interface
space
and
its 0
value is 8.8541878171012
F
/
m
1 36π
109
F/m
The left equation is called Gauss’s law, and it shows that the outward flux of the electric field intensity of an electrostatic field over any closed surface in free space is equal to the ratio of the charge in the closed surface to the permittivity of free space.
《物理双语教学课件》Chapter 17 Electric Potential 电势
1. Newton’s law for the gravitational force and Coulomb’s lawfor the electrostatic force are mathematically identical. Thus the general feature we have discussed for the gravitational force should apply to the electrostatic force.2. In particular, we can infer that the electrostatic force is aconservative force . Thus when that force acts between two or more charged particles within a system of particles, we can assign an electric potential energy U to the system.3. Moreover, If the system changes its configuration from aninitial state i to a different final state f, the electrostatic force does work W on the particles. The resulting change U in thepotential energy of the system is U = U U = W . As withf iother conservative forces, the work done by the electrostatic force is path independent.4. For convenience, we usually take the reference configurationof a system of charged particles to be that in which the particles are all infinitely separated from each other. And we usually set the corresponding reference potential energy to be zero.17.2 Electric Potential1. The potential energy of a charged particle in an electric field depends on the magnitude of the charge. However, the potential energy per unit charge has a unique value at any point in the electric field. Thus the potential energy per unit charge, which can be symbolized as U/q, is independent of the charge q of the particle and is characteristic only as the electric field we are investigating. The potential energy per unit charge at a point in an electric field is called the electric potential V(or simply the potential) at that point . Thus V = U Electricpotential is a scalar, not a vector.2. The electric potential difference V between any two points i and f in an electric field is equal to the difference in potential energy per unit charge between the two point : V = V f V i = q U = q W. The potential difference between two point is thus the negative of the work done by the electrostaticforce per unit charge that move from one point to the other .3. The SI unit for electric potential is the joule per coulomb. This combination occurs so often that a special unit, the volt (abbreviated V) is used to represent it.4. One electron-volt (eV) is the energy equal to the workq .required to move a single elementary charge e through a.potential difference of exactly one volt, so 1eV 1.60 1019 J 17.3 Equi-potential Surfaces1. Adjacent points that have the same electric potential form anequipotential surface, which can be either an imaginary surface or a real, physical surface. No net work W is done on a charged particle by anelectric field when theparticle moves betweentwo points i and f on thesame equipotential surface. See the Figure.2. Figure shows the electric field lines and cross sections ofequipotential surface for several cases. We can find that equipotential surfaces are always perpendicular to electric field lines and thus to E which is always tangent to these lines.17.4 Calculating the Potential from the Field1. We can calculate the potential difference between any twopoints i and f in an electric field if we know the field vectorat all positions along any path connecting those points.2. Consider an arbitraryelectric field, representedby the field lines in theright figure, and a positivetest charge q that moves along the path shown from point ito point f. The differential work done on the particle by theelectrostatic force during a displacement is Thus the total work done on the particle by dW = F . ds = q E . ds .the fields is theintegration of the differential work done on the charge for all the differential displacement along the path. W = q ϕf . d.i Therefore, V V = W = ϕ f . d.f i q i3. If we choose the potential V at point i to be zero, theniV = ϕf . d, in which we have drooped the subscript f. It gives ius the potential V at any point f in the electric field relative to the zero potential at point i.4. Potential due to a point charge: V = 1 q .4几r5. Potential due to a group of point charges: We can find the netpotential at a point due to a group of point charges to sum up the potential resulting from each charge at the given point . V = n V =1 n q i . Here q is the value of the ith charge, and i 4χ r ii =1 0 i =1 ir is the radial distance of the given point from the ith charge. i6. Potential due to an electric dipole : (1) V = 1 p cos 9 . (2)4χ r 2Induced dipole moment: Many molecules such as water(Seeing right figure) have permanentelectric dipole moments. In othermolecules (nonpolar molecules) andin every atom, the centers of thepositive and negative charges coincide and thus no dipole moment is set up. However, if we place an atom or nonpolar molecule in an external electric field, the field distorts the electron orbits and separates the centers of positive and negative charge and sets up a dipole moment that points in the direction of the field. This dipole moment p said to be induced by the field, and the atom or molecule is said to be polarized by the field. When the field is moved, the induced dipole moment and thepolarization disappear. See the figure.7. Potential due to a continuous charge distribution :V = ϕ dV = ϕ 1 dq . Here the integral is to be taken over the4 r 0entire charge distribution. (1) lines of charge; (2)Charged disk.1. The component of E in any direction is the negative of the rate of change of the electric potential with distance in that direction . Ex = ?V ?x ; E y = ?V ?y ; E z = ?V ?z.1. The electric potential energy of a system of fixed point-charges is equal to the work that must be done by external agent to assemble the system, bringing each charge in from an infinite distance .1. An excess charge placed on anisolated conductor will distributeitself on the surface of that conductorso that all points of theconductor-whether on the surface or inside-come to the same potential. This is true regardless of whether the conductor has an internal cavity.2. If an isolated conductor is placed in an external electric field,as in the right figure, all points of the conductor still come toa single potential regardless of whether the conductor has anexcess charge.。
西尔斯当代大学物理双语课件
1.2 Idealized Models
We neglect the size and shape of the ball by representing it as a point object, or particle. We neglect air resistance by making the ball move in a vacuum. point We ignore the earth’s rotation. We make the weight constant.
Chapter 1 Physical Quantities and Vectors
1.1 The nature of physics
• Physics is an experimental science. • Physicists observe the phenomena of nature and try to find patterns and principles that relate these phenomena. These patterns are called physical theories or physical laws, or principles. • Every physical theory has a range of validity. • No theory has ever regarded as the final truth.
Unit prefixes: kilo-, centi-, milli-, micro-, nano
1.3 Standards and Units
Operational definition: kilogram meter second Derived unit: In other cases we define a physical quantity by describing how to calculate it from other quantities that we can measure. speed = distance / time
人教版九年级全册物理第十五章第一节两种电荷教学课件2
演示实验
一些物体被摩擦后，能够吸引轻小物体，称为物体带了电，或者说带了“电荷” 摩擦起电：用摩擦的方法使物体带电，叫摩擦起电。
橡胶棒和毛皮摩擦
橡胶棒和毛皮摩擦后能吸引纸屑 玻璃棒和丝绸摩擦
03
课堂活动
Lorem ipsum dolor sit amet please add your text here lorem ipsum dolor sit amet please add your text here orem ipsum dolor sit amet please add your text here 。Lorem ipsum dolor sit ame
二、原子及其结构
问题与讨论 物体摩擦后为什么会带电，任意两个物体摩擦后都会带电？
1．原子结构
原子 电中性
原子核 带正电
核外电子 带负电
质子 带正电
中子 不带电
原子及其结构
–
2．摩擦起电的原因
+ ++ –
不同物质的原子核束缚电子的本领不同，
–
摩擦后发生了电子得失
失去电子的物体带正电；得到电子的物体 带等量的负电.
课堂导入
小实验：用塑料直尺在头发上摩擦后；气球在墙上摩擦后；都能吸引纸屑
02
演示实验
Lorem ipsum dolor sit amet please add your text here lorem ipsum dolor sit amet please add your text here orem ipsum dolor sit amet please add your text here 。Lorem ipsum dolor sit ame
苏科版九年级物理教材下册双语目录(中英文对照)
九年级下册第十五章电功和电热Chapter 15 Electric power and electric heating15.1 电能表与电功Electricity meters and electrical work15.2 电功率Electrical power15.3 电热器电流的热效应Electric heater and the thermal effect of the current15.4 家庭电路与安全用电Home circuits and safe electricity第十六章电磁转换Chapter 16 Electromagnetic Conversion16.1 磁体与磁场Magnets and magnetic fields16.2 电流的磁场The magnetic field of the current16.3 磁场对电流的作用The effect of magnetic fields on currents16.4 安装直流电动机模型Install the DC motor model16.5 电磁感应发电机Electromagnetic induction and Generator第十七章电磁波与现代通信Chapter 17 Electromagnetic Waves and Modern Communication17.1 信息与信息传播Information and information dissemination17.2 电磁波及其传播Electromagnetic waves and their propagation17.3 现代通信—走进信息时代Modern Communication - Entering the Information Age第十八章能源与可持续发展Chapter 18 Energy and Sustainable Development18.1 能源与社会Energy and society18.2 核能Nuclear energy18.3 太阳能Solar energy18.4 能量转换的基本规律The basic law of energy conversion18.5 能源与可持续发展Energy and sustainable development。
《物理双语教学课件》Chapte...
《物理双语教学课件》Chapte...Chapter 11 The First Law of Thermodynamics11.1Thermodynamics1.With this chapter, we begin a new subject-thermodynamics,which deals with an internal energy of systems, thermal energy, and is governed by a new set of laws.2.The central concept of thermodynamics is temperature. Thisword is so familiar that most of us, because of our built-in sense of hot and cold, tend to be overconfident in our understanding of it.3.Our “temperature sense” is in fact not always reliable. On acolder winter day, for example, an iron railing seems much colder to the touch than a wooden fence post, yet both are at the same temperature. This difference in our sense perception comes about because iron removes energy from our fingers more quickly than wood does.4.Temperature is one of the seven SI base quantities. Physicistsmeasure temperature on the Kelvin scale, which is marked in units called kelvins. Although the temperature of a body apparently has no limit, it does have a lower limit; this limiting low temperature is taken as the zero of the Kelvin temperature scale. Room temperature is about 290 kelvins, or290 K as we write it, abovethis absolute zero . The rightfigure shows the wide rangeover which temperatures aredetermined.11.2 Temperature1. The zeroth law ofthermodynamics : If bodies A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other, and have the same temperature .2. By international agreement, the triple point of water , in which liquid water, solid ice, and water vapor (gaseous water) coexist, has been assigned a value of 273.16 K as the standard fixed-point temperature for the calibration of thermometers.3. Celsius temperatures are measured in degrees, and the Celsius degree has the same size as the kelvin. However, the zero of the Celsius scale is shifted to a more convenient value than absolute zero. IfC T represents a Celsius temperature, then 015.273-=T T C .In expressing temperature on the Celsius scale, the degree symbol is commonly used. Thus we write C 000.20 for a Celsius reading about 293.15 K for a Kelvinreading.4. The Fahrenheit scale , used in the United States, employsa smaller degree than the Celsius scale and a different zero of temperature. The relation between the Celsius and Fahrenheit scales is,32590+=C F T T where F T is Fahrenheit temperature.11.3 The Absorption of Heat by Solids and Liquids1. Heat capacity C of an object is the proportionality constantbetween an amount of heat and the change in temperature that this heat produces in the object. Thus)(i f T T C Q -=, in which i T and f T are the initial and final temperature of theobject. Heat capacity C has the unit of energy per degree or energy per kelvin .2. Two objects made of the same material will have heatcapacities proportional to their masses. It is therefore convenient to define a “heat capacity per unit mass” or specific heat c that refers not to an object but to a unit mass of the material of which the object is made. The above equation then becomes )(i f T T cm Q -=.3. Molar specific heat : In many instances the most convenientunit for specifying the amount of a substance is the mole (mol),where units y elementarr mol 231002.61?= of anysubstance. When quantities are expressed in moles, the specific heat must also involve moles; it is then called a molarspecific heat.11.4 A Closer Look at Heat and Work1. Let us take as our system a gasconfined to a cylinder with amovable piston, as shown inthe figure. The system startsfrom an initial state i ,described by a pressurei p , a volume i V , and a temperaturei T . You want to change the system to a final state f , describedby a pressure f p , a volume f V , and a temperature f T . We assume that all changes occur slowly, with the result that the system is always in (approximate) thermal equilibrium .2. Suppose that you remove a few lead shot from the piston of the Fig., The differential work done by the gas during the displacement is pdV ds pA s d F dW ==?=))(( , in which dV is the differential change in the volume of the gas owing to the movement of the piston.3. If the gas change its volume fromi V to f V , the total workdone by the gas is ??==fi V V pdV dW W .4. There are actually manyways to take the gasfrom state I to state f, asin the figure. So asystem can be takenfrom a given initial stateto a given final state byan infinite number ofprocesses. Heat may ormay not involved, and ingeneral, the workW and heat Q will havedifferent value for different process . So we say that heat andwork are path-dependent quantities .5. The figure (f) shows a thermodynamics cycle in which the system is taken from some initial state i to some other state f ，and then back to i.11.5 The first law of thermodynamics1. You have just seen that when a system changes from a given initial state to a given final state, both work W done and theheat Q exchanged depend on the nature of the process. Experimentally, however, we find a surprising thing. The quantity )(W Q - is the same for all process. It depends only on the initial and final states and does not depend at all on how the system gets from one to the other.2. The quantity W Q - must represent a change in some intrinsic property of the system. We call this property the internal energy int E and we write W Q E E E i f -=-=?int,int,int . This is the first law of thermodynamics . If the thermodynamics system undergoes only a differential change, we can write the first law as dW dQ dE -=int .3. Adiabatic process : An adiabatic process is the process that occurs so rapidly or occurs in a system that is so well insulated that no transfer of heat occurs between the system and its environment. Putting0=Q in the first law then lead to W E -=?int . This tells us that if the work done by the system, the internal energy of the system decreases by the amount of work. Conversely, if work is done on the system, the internal energy of the system increases by that amount .4. Constant-volume process : If the volume of a system is held constant, that system can do no work. Putting0=W in the first law yieldQ E =?int . Thus if heat is added to a system, theinternal energy of the system increases. Conversely, if heat removed during the process, the internal energy of the system must decrease .5. Cyclical process . There are processes in which, after certain interchanges of heat and work, the system is restores to its initial state. In that case, no intrinsic property of the system can possibly change. Putting0int =?E in the first law yield W Q =. Thus the net work done during the process must exactly equal the net amount of heat transferred .6. Free expansion . See the following figure. These are adiabatic processes in which nowork is done on or by thesystem. Thus 0==W Qand the first law requiresthat 0int =?E . A freeexpansion differs from all other processes we have considered because it cannot be done slowly and in a controlled way. As a result, at any given instant during the sudden expansion, the gas is not in thermal equilibrium and its pressure is not the same everywhere. So although we can plot the initial and final states on a p-V diagram, we cannot plot the expansion itself.。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
Chapter 15 Electric Fields
Suppose we fix a positively charged particle q1 in place and then put a second positively charged particle q2near it. From Coulomb's law we know that q1exerts a repulsive electrostatic force on q2. Then you may ask how q1 "know" of the presence of q2? That is, since the charges do not touch, how can q1 exert a force on q2?
This question about action at a distance can be answered by saying that q1 set up an electric field in the space surrounding it. At any given point P in that space, the field has both magnitude and direction.Thus when we place q2at P, q1interacts with q2 through the electric field at P. The magnitude and direction of that electric field determine the magnitude and direction of the force acting on q2.
Another action-at-a-distance problem arises if we move q1, say, toward q2. Coulomb’s law tells us that when q1 is closer to q2, the repulsive electrostatic force acting on q2 must be greater, and it is. Does the electric field at q2, and thus the force acting on q2, change immediately?
The answer is no.Instead, the information about the move by q1travels outward from q1as electromagnetic wave at the
speed of light c . The change in the electric field at q 2, and thus the change in the force acting on q 2, occurs when the wave finally reach q 2.
15.1 The Electric Field
1. The temperature at every point in a room has a definite value. We call the resulting distribution of temperature as temperature field . In much the same way, you can imagine a pressure field in the atmosphere: it consists of the distribution of air pressure values, one for each point in the atmosphere. Theses two examples are of scalar field , because temperature and air-pressure are scalar quantities.
2. The electric field is a vector field
(1) It consists of a distribution of vectors, one for each point in the region around a charged object.
(2) In principle, we can define the electric field at some point near the charged object by placing a positive charge q 0, called a test charge , at the point.
(3) We then measure the electrostatic force
F that acts on the test charge. The electric field
E at point P due to the charged object is defined as 0q
F E .
(4) We represent the electric field at point P with a vector。