电气工程及其自动化专业英语第一章课文翻译.docx

1、电气工程及其自动化专业英语第一章课文翻译第一章第一篇sectiongTwo variables u(t) and i(t) are the most basic concepts in an electric circuit, they characterize the various relationships in an electric circuitu(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 Current The concept of electric charge is the underlying principle fo

2、r explaining all electrical phenomena. Also, the most basic quantity in an electric circuit is the electric charge. Charge is an electrical property of the atomic particles of which matter consists, 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。W

3、e know from elementary physics that all matter is made of fundamental building blocks known as atoms and that each atom consists of electrons, protons, and neutrons. We also know that the charge e on an electron is negative and equal in magnitude to 1019C, while a proton carries a positive charge of

4、 the same magnitude as the electron. The presence of equal numbers of protons and electrons leaves an atom neutrally charged. 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 consider the flow of electric charges. A unique featur

5、e 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 energy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。When a conducting wire is connected to a battery (a so

6、urce of electromotive force), the charges are compelled to move; positive charges move in one direction while negative charges move in the opposite direction. This motion of charges creates electric current. It is conventional to take the currentflow as the movement of positive charges, that is, opp

7、osite to the flow of negative charges, as illustrates. This convention was introduced by Benjamin Franklin (l706l790), the American scientist and inventor. Although we now know that current in metallic conductors is due to negatively charged electrons, we will follow the universally accepted convent

8、ion that current is the net flow of positive charges. Thus, Electric current is the time rate of charge, measured in amperes (A). Mathematically, the relationship among current i, charge q, and time t is 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，

9、与负电荷的流动方向相反，如图11所示。这一惯例是由美国科学家和发明家本杰明富兰克林引入的。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。从数学上来说，电流i、电荷q以及时间t之间的关系是： The charge transferred between time t0 and t is obtained by integrating both sides of Eq. (1-1). We obtain从时间t0到时间t所移送的电荷可由方程（11）两边积分求得。我们算得：The way

10、we define current as i in Eq. (1-l) 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（11）定义电流的方式表明电流不必是一个恒值函数，电荷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 elec

11、tron in a conductor in a particular direction requires some work or energy transfer. This work is performed by an external electromotive force (emf), typically represented by the battery in . This emf is also known as voltage or potential difference. The voltage uab between two points a and b in an

12、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11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 w is energy in joules (J) and q is charge in coulombs (C). The voltage u

13、ab is measured in volts (V), named in honor of the Italian physicist Alessandro Antonio Volta (l745l827), who invented the first voltaic battery. Thus, Voltage (or potential difference) is the energy required to move a unit charge through an element, 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

14、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。 shows the voltage across an element (represented by a rectangular block ) connected to points a and b. The plus (+) and minus (-) signs are used to define reference direction or vol

15、tage polarity. The uab can be interpreted 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 general 图12显示了某个元件（用一个矩形框来表示）两端a、b之间的电压。正号（）和负号（）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

16、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Although 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 recall from physics that power is the

17、time rate of expending or absorbing energy, measured in watts (W). We write this relationship as 虽然电流和电压是电路的两个基本变量，但仅有它们两个是不够的。从实际应用来说，我们需要知道功率和能量。为了把功率和能量同电压、电流联系起来，我们重温物理学中关于功率是消耗或吸收的能量的时率，它是以瓦特为单位来度量的。我们把这个关系式写成：Where p is power in watts (W), w is energy in joules (J), and t is time in seconds (s

18、). From Eq. (1-1), Eq. (1-3), and Eq. (1-5), it follows that 式中p是以瓦特为单位的功率，w是以焦耳为单位的能量，t是以秒为单位的时间，从方程（11）、（13）和（15）可以推出Because u and i are generally function of time, the power p in Eq. (1-6) is a time-varying quantity and is called the instantaneous power. The power absorbed or supplied by an eleme

19、nt is the product of the voltage across the element and the current through it. If the power has a plus sign, power is being delivered to or absorbed by the element. If, on the other hand, the power has a minus sign, power is being supplied by the element. But how do we know when the power has a neg

20、ative or a positive sign由于u和i通常是时间的函数，方程（16）中的功率p是个时间变量于是被称为瞬时功率，某一元件吸收或提供的功率等于元件两端电压和通过它的电流的乘积。如果这个功率的符号是正的，那么功率向元件释放或被元件吸收。另一方面，如果功率的符号是负的，那么功率是由元件提供的。但我们如何得知何时功率为正或为负Current direction and voltage polarity play a major role in determining the sign of power. It is therefore important that we pay at

21、tention to the relationship between current i and voltage u in (a). The voltage polarity and current i direction must conform with those shown in (a) in order for the power to have a positive sign. This is known as the passive sign convention. By the passive sign convention, current enters through t

22、he positive polarity of the voltage. In this case, p = ui or ui 0 implies that the element is absorbing power. However, if p = -ui or ui 0, as in (b), the element is releasing or supplying power. 在我们确定功率符号时，电流的方向和电压的极性起着主要的作用，这就是我们在分析图13（a）所显示的电流i和电压u的关系时特别谨慎的重要原因。为了使功率的符号为正，电压的极性和电流的方向必须与图13（a）所示的一

23、致。 这种情况被称为无源符号惯例，对于无源符号惯例来说，电流流进电压的正极。在这种情况下，pui或ui0，表明元件是在吸收功率。而如果pui或ui 0, then terminal a is at a higher potential than terminal b. The opposite is true, of course, if u 0，那么a端的电位高于b端，当然，如果u0，反之亦然。In (a), the voltage u may be time varying, or it may be constant, in which case we would probably la

24、bel it U. Another symbol that is often used for a constant voltage source, such as a battery with U volts across its terminals, is shown in (b). In the case of constant sources we shall use (a) and 1-4(b) interchangeably.在图14（a）中，电压u可以是随时间而变化，或者可以是恒定的，在这种情况下我们可能把它标为U，对于恒定电压源我们通常使用另一种符号，例如在两端只有U伏电压的电

25、池组，如图14（b）所示。在恒定源的情况下我们可以交替地使用于图14（a）或图14（b）We might observe at this point that the polarity marks on (b) are redundant since the polarity could be defined by the positions of the longer and shorter lines. 我们可能已经注意到这一点，即图14（b）中的极性标号，是多余的因为我们可以根据长天线的位置符，确定电池极性An independent current source is a two-te

26、rminal element through which a specified current flows. The current is completely independent of the voltage across the element. The symbol for an independent current source is shown in , where i is the specified current. The direction of the current is indicated by the arrow一个独立电流源是二端元件在两端之间特定的电流流过，该电流完全独立于元件两端的电压，一个独立电流源的符合如图15所示。图中i是特定电流，该电流的方向由箭头标明Independent sources are usually meant to deliver power to the external circuit and not to absorb it. Thus if u is the voltage across the source and its current i is directed out of the positive terminal, then the source is del