电气工程与自动化专业英语课件1-2

1、Chapter 1 Fundamentals of Electric Circuits,Section 2 Circuit Elements,Text,New Words and Expressions,Exercises,End,Translation Standard,Section2 Circuit Elements,An electric circuit is simply an interconnection of the elements. There are two types of elements found in electric circuits: passive ele

2、ments and active elements. An active element is capable of generating energy while a passive element is not. Examples of passive elements are resistors, capacitors, and inductors. The most important active elements are voltage or current sources that generally deliver power to the circuit connected

3、to them.,Section2 Circuit Elements,Independent sources An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit variables. An independent voltage source is a two-terminal element, such as a battery or a generator, w

4、hich maintains a specified voltage between its terminals. The voltage is completely independent of the current through the element. The symbol for a voltage source having u volts across its terminals is shown in Fig.1-4(a). The polarity is as shown,Section2 Circuit Elements,indicating that terminal

5、a is u volts above terminal b. Thus if u 0, then terminal a is at a higher potential than terminal b. The opposite is true, of course, if u 0. In Fig.1-4(a), the voltage u may be time varying, or it may be constant, in which case we would probably label it U. Another symbol that is often used for a

6、constant voltage source, such as a battery with U volts across its terminals, is shown in Fig.1-4(b). In the case of constant sources we shall use Fig.1-4(a) and 1-4(b) interchangeably.,Section2 Circuit Elements,We might observe at this point that the polarity marks on Fig.1-4(b) are redundant since

7、 the polarity could be defined by the positions of the longer and shorter lines.,Fig.1-4 Symbols for independent voltage sources (a) used for constant or time-varying voltage; (b) used for constant voltage (dc).,Section2 Circuit Elements,An independent current source is a two-terminal element throug

8、h 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 Fig.1-5, where i is the specified current. The direction of the current is indicated by the arrow.,Fig.1-5 Symbols for independent curr

9、ent sources,Section2 Circuit Elements,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 delivering power, given by p = ui, to t

10、he external circuit. Otherwise it is absorbing power. For example, in Fig.1-6 (a) the battery is delivering 24 W to the external circuit. In Fig.1-6(b) the battery is absorbing 24 W, as would be the case when it is being charged.,Section2 Circuit Elements,Fig.1-6 Symbols for independent sources (a)

11、A source delivering power; (b) A source absorbing power,Section2 Circuit Elements,Dependent sources An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current. Dependent sources are usually designated by diamond-shaped symb

12、ols, as shown in Fig.1-7.,Fig.1-7 Symbols for dependent sources (a) Dependent voltage source; (b) Dependent current source,Section2 Circuit Elements,Since the control of the dependent source is achieved by a voltage or current of some other element in the circuit, and the source can be voltage or cu

13、rrent, it follows that there are four possible types of dependent sources, namely: （1）A voltage-controlled voltage source (VCVS). （2）A current-controlled voltage source (CCVS). （3）A voltage-controlled current source (VCCS). （4）A current-controlled current source (CCCS). Dependent sources are useful

14、in modeling elements such as transistors, operational amplifiers and integrated circuits.,Section2 Circuit Elements,It should be noted that an ideal voltage source (dependent or independent) will produce any current required to ensure that the terminal voltage is as stated, whereas an ideal current

15、source will produce the necessary voltage to ensure the stated current flow. Thus an ideal source could in theory supply an infinite amount of energy. It should also be noted that not only do sources supply power to a circuit, but they can absorb power from a circuit too. For a voltage source, we kn

16、ow the voltage but not the current supplied or drawn by it. By the same token, we know the current supplied by a current source but not the voltage across it.,Return,New Words and Expressions,activea. 有源的，有功的，有效的 活动的，主动的，积极的 活性的，放射的，激励的 active element 有源元件 resistorn 电阻，电阻器 capacitorn. 电容器 inductorn.

17、 电感器 sourcen. 电源，（光，能，动力，信号，辐射，根，来，起）源 voltage source 电压源 current source 电流源 ideal independent source 理想独立源,New Words and Expressions,constant voltage source恒定电压源 independent source独立源 dependent source 受控源 controlled source受控源 voltage-controlled voltage source电压控制电压源 current-controlled voltage sourc

18、e电流控制电压源 voltage-controlled current source电压控制电流源 current-controlled current source电流控制电流源,New Words and Expressions,generator n. 发电机 （脉冲，信号，气体）发生器，振荡器，加速器 AC generator 交流发电机 diamond-shaped a. 菱形的 transistor n. 晶体管，半导体管 operational a. 运算的，计算的 操作的，工作的，业务的，运转的 amplifier n. 放大器 integrated circuit 集成电路,

19、New Words and Expressions,tokenn. 标记，象征，记号 特征，证明 by the same token 同理，同样；另外，还有,Return,Translation Standard,准确明白,通顺严密,简练全面,专业英语翻译是对原文的一种再创作，其标准为,Translation Standard,掌握英语语法知识,具有一定深度的专业知识和较为广博的科学知识,有较高的汉语修养,为达到以上翻译标准，必须做到：,掌握翻译方法和技巧,Return,Exercises,I. Choose the best answer into the blank,1. An indep

20、endent voltage source is a , which maintains a specified voltage between its terminals. A. one-terminal element B. two-terminal element C. three-terminal element D. four-terminal element 2. Resistors are elements. A. passive B. active C. independent source D. dependent source,Exercises,I. Choose the

21、 best answer into the blank,3. An ideal dependent source is an element in which the source quantity is controlled by another voltage or current. A. passive B. active C. independent D. inductive 4. There are possible types of dependent sources. A. two B. three C. four D. five,Exercises,I. Choose the

22、best answer into the blank,5. For a voltage source, its terminal voltage is known but its must be determined by the external circuit connecting with it. A. electromotive forceB. current C. control coefficientD. polarity,Exercises,II. Answer the following questions according to the text,1. What diffe

23、rence is there between an independent source and a dependent source? 2. What element is an ideal independent source? 3. Is the voltage of an independent voltage source dependent of the current through the element? How to find the current through it? 4. What are four possible types of dependent sourc

24、es? 5. Is the terminal voltage of independent voltage source always constant?,Exercises,III. Translate the following into Chinese,All the simple circuit elements that will be considered in the work that follows can be classified according to the relationship of the current through the element to the voltage across th