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1、第一章第一篇sectiongTwo variables u(t) and i (t) are the most basic concepts in an electric circuit, they characterize the various relati on shipsin an electriccircuitu(t)和i(t)这两个变量是电路中最基本的两个变量，它们刻划了电路的各种关 系。Charge and Curre ntTheconcept of electric charge is the underlyingprincipleforexplaining all elect
2、ricalphenomena. Also, the most basic quantity in anelectric circuit is the electric charge. Charge is an electrical property of the atomic particles of which matter con sists, measured in coulombs (C).电荷和电流电荷的概念是用来解释所有电气现象的基本概念。也即，电路中最基本 的量是电荷。电荷是构成物质的原子微粒的电气属性，它是以库仑为单位来度量的。We know from eleme ntary
3、physics that all matter is made of fun dame ntal building blocks known as atoms and that each atom consists of electrons, prot ons, and n eutr ons. We also know that the chargee on an electr on isnegative and equal in magnitude to 1.60210 x 10-19C, while a proton carries a positive charge of the sam
4、e magnitude as the electron. The presenee of equal numbers of protons and electrons leaves an atom neutrallycharged.我们从基础物理得知一切物质是由被称为原子的基本构造部分组成的， 并且每个原子是由电子，质子和中子组成的。我们还知道电子的电量是负的并且 在数值上等于1.602100 x 10-12C，而质子所带的正电量在数值上与电子相等。 质子和电子数量相同使得原子呈现电中性。We con sider the flow of electric charges. A unique f
5、eature of electric charge or electricity is the fact that it is mobile; that is, it can be transferred from one place to another, where it can be converted to another form of en ergy 让我们来考虑一下电荷的流动。电荷或电的特性是其运动的特性，也就是，它可以从一个地方被移送到另一个地方，在此它可以被转换成另外一种形式的能量。Whena con duct ing wire is conn ected to a batt
6、ery (a source of electromotive force), the charges are compelled to move; positive charges move in one directi on while n egative charges move in the opposite directio n. This motion of charges creates electric current. It is conventional to take the curre ntflow as the moveme nt of positive charges
7、, that is, opposite to the flow of negative charges, as Fig.l-1 illustrates. This convention was introduced by Benjamin Franklin (l706 l790), the American scientist and inven tor. Although we now know that curre nt in metallic con ductors is due to n egatively charged electr ons, we will follow the
8、uni versally accepted convention that current is the net flow of positive charges. Thus, Electric current is the time rate of charge, measured in amperes (A).Mathematically, the relati on ship among curre nti , charge q, and time tis当我们把一根导线连接到某一电池上时（一种电动势源），电荷被外力驱 使移动；正电荷朝一个方向移动而负电荷朝相反的方向移动。这种电荷的移动
9、产 生了电流。我们可以很方便地把电流看作是正电荷的移动， 也即，与负电荷的流 动方向相反，如图1 1所示。这一惯例是由美国科学家和发明家本杰明一富兰 克林引入的。虽然我们现在知道金属导体中的电流是由负电荷引起的，但我们将遵循通用的惯例，即把电流看作是正电荷的单纯的流动。 于是电流就是电荷的时 率，它是以安培为单位来度量的d。从数学上来说，电流 i、电荷q以及时间t之 间的关系是：i二竺二dti fThe charge transferredbetween time 10 and t is obtainedbyintegrating both sides of Eq. (1-1). We obt
10、ain从时间t0到时间t所移送的电荷可由方程(1 1)两边积分求得。我们算得：tqpidt(42)The way we define current as i in Eq. (1-1) suggests that current need not be a constant-valued function, charge can vary with time in several ways that may be represented by different kinds of mathematical functions 我们通过方程(1 1)定义电流的方式表明电流不必是一个恒值函数，电荷
11、可以不同的方式随时间而变化，这些不同的方式可用各种数学函数表达出来。电压，能量和功率To move the electro n in a con ductor in a particular directi onrequires some work or energy transfer.This work is performed by anexternal electromotive force (emf), typicallyrepresented by the batteryin Fig .l-1. This emf is also known as voltage or potenti
12、al differe nee.The voltage uab between twdq points a and b in an electric circuit is the energy (or work) needed to move a unit charge from a to b; mathematically 在导体中朝一个特定的方向移动电荷需要一些功或者能量的传递，这个功是由外部的电动势来完成的。图1 1所示的电池就是一个典型的例子。这种电动势也 被称为电压或电位差。电路中a、b两点间的电压等于从a到b移动单位电荷所 需的能量(或所需做的功)。数学表达式为：where wis
13、energy in joules (J) and q is charge in coulombs (C). The voltage uab is measured in volts (V), named in honor of the Italian physicistAlessa ndro Antonio Volta (1745l827), who inven ted the first voltaicbattery. Thus, Voltage (or potentialdifferenee) is the energy requiredto move a unit charge thro
14、ugh an eleme nt, measured in volts (V).式中w是单位为焦耳的能量而q是单位为库仑的电荷。电压Uab是以伏特为单位 来度量的，它是为了纪念意大利物理学家 Alessandro Antonio Volta而命名的， 这位意大利物理学家发明了首个伏达电池。 于是电压(或电压差)等于将单位电 荷在元件中移动所需的能量，它是以伏特为单位来度量的。Fig.1-2 shows the voltage across an element (represented by a rectangular block ) conn ected to points a an d b.
15、 The plus (+) and minus (-) sig ns are used to defi ne refere nee direct ion or voltage polarity. Theuab can beinterpreted in two ways: point a is at a potential of uab volts higher than point b;the potential at point a with respect to point b is uab. It follows logically that in gen eral图1-2显示了某个元件
16、（用一个矩形框来表示）两端a、b之间的电压。正号（+ ） 和负号（一）被用来指明参考方向或电压的极性，Uab可以通过以下两种方法来解释。1）在Uab伏特的电位中a点电位高于b点，2） a点电位相对于b点而言 是Uab,通常在逻辑上遵循Uab = - UbaAlthough current and voltage are the two basic variables in an electric circuit, they are not sufficient by themselves. For practical purposes, we need to know power and energy. To relate power and energy to voltage and current,we recallfr
