专业英语复习题.doc

1、 Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs 。2、 We also know that the charge e on an electron is negative and equal in magnitude to 1.60210 10-19Cwhile a proton carries a positive charge of the same magnitude as the electron3. 、A unique feature 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. 4、 Although we now know that current in metallic conductors is due to negatively charged electrons, we will follow the universally accepted convention that current is the net flow of positive charges.5、 The way 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.6、 The voltage uab between two points a and b in an electric circuit is the energy (or work) needed to move a unit charge from a to b。7、 The power absorbed or supplied by an element is the product of the voltage across the element and the current through it. 8、 An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit variables.9、 The symbol for a voltage source having u volts across its terminals is shown in Fig.1-4(a).10、 Another symbol that is often used for a constant voltage source, such as a battery with U volts across its terminals, is shown in Fig.1-4(b).11、 We might observe at this point that the polarity marks on Fig.1-4(b) are redundant since the polarity could be defined by the positions of the longer and shorter lines. 12、 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 the external circuit.13、 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 current, it follows that there are four possible types of dependent sources, namely:14、 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 source will produce the necessary voltage to ensure the stated current flow. 15、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 the element.16、 Furthermore, we shall need to define special kinds of sources in which the source voltage or current depends upon a current or voltage elsewhere in the circuit; such sources will be termed dependent sources or controlled sources. 17、 The circuit element used to model the current-resisting behavior of a material is the resistor.18、 Obviously, a straight line is the only graph possible for which the ratio of u(t) to i(t) is constant for all i(t).19、 Resistors whose resistances do not remain constant for different terminal currents are known as nonlinear resistors. 20、 In reality, all practical resistors are nonlinear because the electrical characteristics of all conductors are affected by environmental factors such as temperature.21、 Resistors may be easily purchased or manufactured, but it is soon found that the voltage-current ratio of this physical device is reasonably constant only within certain ranges of current, voltage, or power and depends also on temperature and other environmental factors.22、 A different class of relationship occurs because of the restriction that some specific type of network element places on the variables. Still another class of relationship is one between several variables of the same type which occurs as the result of the network configuration, i.e., the manner in which the various element of the network are interconnected. 23、24、 Kirchhoffs Current Law (KCL) states that the algebraic sum of currents entering a node (or a closed boundary) is zero.25、 An alternative form of KCL: The sum of the currents entering a node is equal to the sum of the currents leaving the node. 26、 Kirchhoffs Voltage Law (KVL) states that the algebraic sum of all voltages around a closed path (or loop) is zero.27、 The sign on each voltage is the polarity of the terminal encountered first as we travel around the loop.28、 With the two techniques to be developed in this section, we can analyze almost any circuit by obtaining a set of simultaneous equations that are then solved to obtain the required values of current or voltage.29、 A convenient choice of voltages for many networks is the set of node voltages. 30、 Frequently the reference node is chosen to be the node to which the largest number of branches are connected.31、 The chassis may then be called ground, and it becomes the logical choice for the reference node.32、 Clearly, simplification in writing the resulting equations is possible when the reference node is chosen to be a node with a large number of elements connected to it.33、 identifying it by the ground connection shown.34、 These two voltages are sufficient, and the voltage between any other pair of nodes may be found in terms of them.35、 We do this by equating the total current leaving the node through the several conductances to the total source current entering the node.36、 Using mesh currents instead of element currents as circuit variables is convenient and reduces the number of equations that must be solved simultaneously.37、 A planar circuit is one that can be drawn in a plane with no branches crossing one another; otherwise it is nonplanar. 38、 A mesh current is indicated by a curved arrow that almost closes on itself and is drawn inside the appropriate mesh, as shown in Fig.1-16. 39、 Although the direction is arbitrary, we shall always choose clockwise mesh currents because a certain error-minimizing symmetry then results in the equations. 40、 Impedance is not a phasor and cannot be transformed to the time domain by multiplying by ejt and taking the real part.41、 We can proceed to our simplification of sinusoidal steadystate analysis by establishing the relationship between the phasor voltage and phasor current for each of the three passive elements. 42、 We should note from Eq. (1-24) that the voltage and current relation is in phase, as illustrated in the phasor diagram in Fig.1-18. 43、 The phase sequence is the time order in which the voltages pass through their respective maximum values. The phase sequence is determined by the order in which the phasors pass through a fixed point in the phasor diagram. 44、 This is due to the ease with which loads may be added or removed from each phase of a delta-connected load.45、 On the other hand, delta-connected sources are not common in practice because of the circulating current that will result in the delta-mesh if the three-phase voltage are slightly unbalanced. 46、 The wye source connection is used for long distance transmission of electric power, where resistive losses (I 2R) should be minimal. 47、 This conversions from three-phase to single-phase is required in residential wiring because household lighting and appliances use single-phase power. 48、 In every aspect of our increasingly technological society whether it is science, engineering, medicine, music, maintenance, or even espionagethe role of electronics is large, and it is growing.49、 This information might involve speech and music, as in radio broadcasting, a physical quantity such as the temperature of the air in a room, or numerical data, such as the record of stock market transactions.50、51、 A signal-processing system is an interconnection of components and devices that can accept an input signal or a group of input signals, operate on the signals in some fashion either to extract or improve the quality of the information, and present the information as an output in the proper form at the proper time. 52、 Analog electronics pertains to those systems in which the electrical voltage and electrical current are analogous to physical quantities and vary continuously.53、 Analog electronic circuits are carefully designed to make the electrical voltages and currents follow the input signal.54、 The body of thought that is known collectively as symbolic logic established the principles for deriving mathematical proofs and singularly modified our understanding and the scope of mathematics. 55、 Boole and others were interested in developing a systematic means of deciding whether a proposition in logic or mathematics was true or false, but we shall be concerned only with the validity of the output of digital devices.56、 In developing digital systems the easiest procedure is to put together conceptually the gates and connections to perform the assigned task in the most direct way. 57、 The equivalent simplified combination of gates will probably be much less expensive and less difficult to assemble.58、 There are many different ways to build electronic circuits with input-output characteristics that correspond to the various digital operations.59、 Occasionally, one must make connections between digital circuits constructed from logic families with input and output voltage ranges that are not compatible with one another.60、 The digital representation of the values is important for digital processing and analysis, for regulation and control, and for recording and transmitting the data that quantize them.61、 The clarity and fidelity of laser-read digital recordings of music and speech and the freedom of these recordings from background noise are recent advancements, but the human ear cannot convert binary data recorded on a disc to music or speech.62、 The transducer is the name of the device that produces a voltage or a current proportional to the physical phenomenon to which it responds.63、 the voltage is derived from the sensitive element in an electrical circuit, as when a temperature sensitive resistor and a constant resistance form a voltage divider whose voltage is related directly to the temperature.64、 The other technique is to integrate the analog signal and to use the measured time (a given number of clock pulses) for the amplitude of the integral to reach a value to establish an equivalent binary number.65、 The bipolar inverter is the basic circuit from which most bipolar saturated logic circuit are developed, including diode-transistor logic (DTL) and transistor-transistor logic (TTL). 66、 Transistor-transistor logic, which evolved directly from DTL, provides reduced propagation delay times, as we will show. 67、 They became the foundation of analog computers, at one time analog computers were called differential analyzers because they are used to solve differential equations. 68、 The analog amplifier consists of a basic difference amplifier, implemented by feedback and other compensating amplifying circuits to give linear response, stability, freedom from drift, and other desirable properties.69、 Thus it is more difficult to isolate the long-term changes that arise from variations in temperature and power-supply voltage and from other effects that cause the output voltage to drift. 70、 The availability of operational amplifiers as integrated circuits in the form of dual in-line packages (DIPs) or in other compact forms makes the solution of analog signal problems analogous in many respects to the solution of digital logic problems, that is, through the interconnection of integrated circuits.71、 inputs, the output of the operational amplifier will be at the maximum (saturated) value if the voltage at the noninverting input is larger than the voltage at the inverting input。如果两个不同的正电压分别被加在两个输入端，而且非倒向输入端的电压大于倒向输入端的电压，那么运算放大器的输出端电压将处于最大值（饱和值）。72、 We will see that an operational amplifier is an excellent voltage comparator because it produces a large voltage swing at the instant of crossing, when an earlier relation in voltage magnitudes is reversed by only a few microvolts. 我们将看到运算器是非常好的电压比较器，因为它在瞬间电压变换时产生很大的电压起伏。此时仅仅几微伏的电压将使先前的电压大小关系产生逆转。73、 When a portion of the output signal is returned to the input as negative feedback, the voltage difference cannot grow large because the output changes to minimize the voltage difference between the inputs.当输出信号的一部分返回输入端作为负反馈，电压差就无法增大因为输出改变使输入端的电压差减小。74、 To summarize, a good operational amplifier is characterized by a very large open-circuit gain of a million or so, an extremely small difference voltage between the inverting and the noninverting input terminals, a very high input impedance, and a small output impedance.概括起来，一个好的运算放大器具有以下特性，非常大的大约一百万的开路增益，倒向输入端和非倒向输入端之间相当小的电压差；很高的输入阻抗以及很小的输出阻抗。75、 The other limitation is the rate at which most operational amplifiers can respond to a step change in the input signal. 另外一个局限是大多数运算放大器对输入信号的改变所能起反应的速率。76、 Operational amplifiers and digital logic gates used together allow data to be processed and analyzed with the greatest advantages of both technologies. 同时应用运算放大器和逻辑门的电路因为具有两种技术优势而允许进行数字处理和分析。77、 The op-amp is prevalent in analog electronics, and can be thought of as another electronics device, in much the same way as the bipolar or field-effect transistor.运算放大器在模拟电子学中很常用， 并且它在很多方面与二极管或场效应 管一样， 可以被视为另一种电子设备。 78、 Op-amps, in conjunction with resistors and capacitors, were used in analog computer to perform mathematical operation to solve differential and integral equations.运算放大器与电阻器和电容器连接在一起， 被应用在模拟计算机中用来 完成数学运算以求解微分方程和积分方程。 79、 The maximum output was determined by specifying that the output transistor was saturation region and also by specifying a maximum collector current in the output transistor. 最大输出取决于确定输出晶体管工作在饱和区并且确定输出晶体管 的集电极电流处于最大值。80、 Such converters are very popular in the battery-operated power systems such as the uninterruptible power supplies (UPS) for hospitals, and AC motor drives.这种转换器是一种很受欢迎的电池驱动的电力系统如不间断电源系统(UPS)为医院、交流电动机驱动的81、 Analyses of DC-AC converter circuits at low and high frequencies are very similar except that at high frequencies the parasitic capacitances and inductances, charge storage, and heat localizing problems in switching devices must be taken into account. 析了DC-AC转换器电路的低阻和高频率是非常相似的,除了在高频寄生和电感,各充电储存和热本地化交换设备中存在的一些问题,必须同时兼顾。82、 Input is from a DC source and the output is desired to be a sinusoidal voltage or current with zero DC component, single-phase or three-phase signal.从直流输入和输出,是理想的来源是一个正弦电压或电流为零,单相或三相直流分量信号。83、 Switches including the diodes are assumed to be ideal and unidirectional, that is, they have zero on-state losses, zero off-state losses, zero switching losses and unrestricted voltage or current carrying capabilities.开关包括二极管被认为是理想的和单向的,也就是说,他们具有零损失,零off-s