电气专业英语课文翻译13页.doc

An electric circuit (or network) is an interconnection of physical electrical device. The purpose of electric circuits is to distribute and convert energy into some other forms. Accordingly, the basic circuit components are an energy source (or sources), an energy converter (or converters) and conductors connecting them. 电路（或者网络）是物理电气设备的一种互相连接电路的目的是为了将能量分配和转换到另外一种形式中因此，基本的电路元件包括电源、电能转换器以及连接它们的导体An energy source (a primary or secondary cell, a generator and the like) converts chemical, mechanical, thermal or some other forms of energy into electric energy. An energy converter, also called load (such as a lamp, heating appliance or electric motor), converts electric energy into light, heat, mechanical work and so on. 电源（原生电池或者再生电池、发电机等类似装备）将化学能量、机械能量，热能或者其他形式的能量转换成电能。

电能转换器（也称为负载，如灯泡、电热器或者电动机）将电能转换成光、热、机械运动等等 Events in a circuit can be defined in terms of e.m.f. (or voltage) and current. When electric energy is generated, transmitted and converted under conditions such that the currents and voltages involved remain constant with time, one usually speaks of direct-current (D.C.) circuits. 电路属性可以根据电动势和电流来定义当电能在产生、传输和变换时，若电路中相关的电流和电压不随时间而变化，我们便称其为直流电路With time-invariant currents and voltages, the magnetic and electric fields of the associated electric plant are also time-invariant. This is the reason why no e.m.f.s of self-(or mutual-)induction appear in D.C. circuits, nor are there any displacement currents in the dielectric surrounding the conductors. 在电流和电压时不变的情况下，相关电气设备的电磁场也是时不变的。

这就是为什么直流电路中没有自（互）感电动势、以及围绕在导体附近的电介质没有位移电流Fig.1.1 shows in simplified form a hypothetical circuit with a storage battery as the source and a lamp as the load. The terminals of the source and load are interconnected by conductors (generally but not always wires). 图1.1给出了一个假设电路的简单形式：一个蓄电池作为电源、以及一个灯泡作为负载电源和负载的终端用导体互相连接，通常这种导体是导线，但少数情况下也有例外As is seen, the source, load and conductors form a closed conducting path. The e.m.f. of the source causes a continuous and unidirectional current to circulate round this closed path.如图所示，电源、负载和导体构成了一个闭合导电回路。

电源的电动势产生一个连续的单方向电流在闭合回路中流通The simple circuit made up of a source, a load and two wires is seldom, if ever, met with in practice. Practical circuits may contain a large number of sources and loads interconnected in a variety of ways. 这种由一个电源、一个负载和两根导线组成的简单电路在实践中即使有时能遇到，也是很少见的实际的电路包括很多用不同方法连接起来的电源和负载 To simplify analysis of actual circuits, it is usual to show them symbolically in a diagram called a circuit diagram, which is in fact a fictitious or, rather, idealized model of an actual circuit of network. Such a diagram consists of interconnected symbols called circuit elements or circuit parameters. 为了简化分析，通常用电路图来象征性地表示实际的电路。

实际上，电路图是实际电路的一个假设模型，或相当于一个理想模型这样的电路图包括电路元件或者电路参数等互联符号Two elements are necessary to represent processes in a D.C. circuit. These are a source of e.m.f. E and of internal (or “source”) resistance RS, and the load resistance (which includes the resistance of the conductors) R (Fig.1.2). 在直流电路中，有两个元件是有必要描绘出来处理的这就是电源的电动势E、内阻RS，以及负载电阻R（其中包含了导体电阻）Whatever its origin (thermal, contact, etc.), the source e.m.f. E(Fig.1.2(a)) is numerically equal to the potential difference between terminals 1 and 2 with the external circuit open, that is, when there is no current flowing through the source.无论图1.2(a)中的电动势E的原动力是什么（即不论是热的、机械的还是其它什么形式），其大小就等于1、2两端之间的开路电压，也就是电源没有电流通过的情况。

The source e.m.f. is directed from the terminal at a lower potential to that at a higher one. On diagram, this is shown by arrows. 电动势从较低电压端指向较高电压端，这在图表中用箭头表示 When a load is connected to the source terminals (the circuit is then said to be loaded) and the circuit is closed, a current begins to flow round it. Now the voltage between source terminals 1 and 2 (called the terminal voltage) is not equal to its e.m.f. because of the voltage drop VS inside the source, that across the source resistance RS . 当一个负载加在电源两端（也就是说电路被加上负载），同时电路闭合，就有电流开始流通。

这时在电源1、2两端之间的电压（称为端电压）不等同于电源的电动势，因为这时电源内阻RS两端将产生电压降VS Fig.1.3 shows a typical so-called external characteristic of a loaded source (hence another name is the load characteristic of a source). As is seen, increase of current from zero to I~I1 causes the terminal voltage of the source to decrease linearly 图1.3表示带负载电源的一个典型的外特性（由于电源带负载，所以也称为电源的负载特性）如图所示，当电流从0增加到I1时，引起电源端电压的线性减小In other words, the voltage drop VS across the source resistance rises in proportion to the current. This goes on until a certain limit is reached. Then as the current keeps rising, the proportionality between its value and the voltage drop across the source is upset, and the external characteristic ceases to be linear. 换句话说，横跨电源内阻的电压降与电流成比例的增长，这种增长趋势一直持续到一个特定的限值。

然后当电流继续增加时，电流值与横过电源的电压降之间的比例关系被扰乱，使得外特性终止线性关系This decrease in voltage may be caused by a reduction in the source voltage, by an increase in the internal resistance, or both. The power delivered by a source is given by the equality PS=EI, where PS is the power of the source。