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1、Chapter 1 Electric and Electronic Technology FundamentalsUnit 1 Electric Elements and Components Text New Words and Expressions Exercises EndUnit1 Electric Elements and Components Introduction Electrical elements are conceptual abstractions used in the analysis of electrical networks. Any electrical

2、 network can be analyzed as multiple, interconnected electrical elements in a schematic diagram or circuit diagram, each of which affects the voltage in the network or current through the network.These ideal electrical elements represent real, physical electrical or electronic components but they do

3、 not exist physically and they are assumed to have ideal properties according to a lumped element model, while components are objects with less than ideal properties, a degree of uncertainty in their values and some degree of nonlinearity, each of which may require a combination ofmultiple electrica

4、l elements in order to approximate itsfunctions. Circuit analysis using electric elements is useful for understanding many practical electrical networks using components. By analyzing the way a network is affected by its individual elements it is possible to estimate how a real network will behave.U

5、nit1 Electric Elements and Components The elements The four fundamental circuit variables are current, I; voltage, V, charge, Q; and magnetic flux, . Only 5 elements, produced by manipulating these four variables, are required to represent any component or network in a Linear system.Two sources: Cur

6、rent source, measured in amperes - produces a current in a wire. An ideal current source is a mathematical model, which real devices can only approach in performance. The current through an ideal current source is independent of the voltage across it.Unit1 Electric Elements and Components Voltage so

7、urce, measured in volts - produces a potential difference across two points. An ideal voltage source is only exists in mathematical models of circuits. Similarly, the voltage across an ideal voltage source is independent of the current through it.Three passive elements: Resistance R, measured in ohm

8、s - produces a voltage proportional to the current flowing through the element. Relates voltage and current according to the relation Capacitance C, measured in farads - produces a current proportional to the rate of change of voltage across the element. Relates charge and voltage according to theUn

9、it1 Electric Elements and ComponentsrelationUnit1 Electric Elements and Components. Inductance L, measured in henries - produces a voltage proportional to the rate of change of current through the element. Relates flux and current according to therelation . The Components A battery provides electrom

10、otive force (emf), or voltage, in a circuit. It contains layers of chemicals that cause electrons to move in a certain direction, from its negative pole to its positive pole. It is marked with a rating of how much voltage there is across the two poles, and a (-) for the negative pole and a (+) for t

11、he positive pole. Batteries may also be marked with an ampere hour (Ah) rating, indicating total charge capacity. An ideal battery can thus be represented as a voltage source. In practice, a battery also has an internal resistance that is represented as a resistance in series with the voltagesource.

12、 Unit1 Electric Elements and Components If a wire is used to connect the two poles of a battery, electrons flow through the wire from the negative end to the positive end. (The wire will also get hot because it isnt a perfect conductor, and the battery will quickly exhaust all its power.) Thus a wir

13、e can be represented as a low-value resistor. Current sources are often absent from basic electric circuits, and are more likely to be found in electronic circuits containing semiconductors. For example, on a first degree of approximation, a bipolar (junction) transistor may be represented by a vari

14、able current source that iscontrolled by the input voltage.Unit1 Electric Elements and Components A resistor is a component whose function is to regulate the current in the circuit. One common kind is a little cylinder of graphite with metal wires coming out of either end. These are painted with col

15、ored stripes that indicate the resistance, in ohms, and the tolerance, in percent. This system is called the resistor color code. Another kind of resistor is a filament, which is a coil of metal wire that can withstand high temperature but has a finite resistance. When a current is passed through a

16、filament, it heats up because of this resistance. Filaments are commonly used in light bulbs and heaters. They are marked with the voltage that should be applied to them, and the power, in watts, that they will then give off as light and heat. Due to the effect of heating, a filaments resistance is

17、higher when it is hotthan when it is cold. Unit1 Electric Elements and Components An electric charge can be stored and then quickly released by a component called a capacitor. A common type of capacitor consists of two pieces of metal foil (or plates) with an insulator (the dielectric) such as waxed

18、paper between them. If an electric charge is placed on the plates of a capacitor, it will stay there because it cant cross the insulator to the other plate. If a wire is then connected between the two plates, the charge will flow through the wire to balance the charges on the opposite platesthecapac

19、itor is then said to be discharged. Unit1 Electric Elements and ComponentsUnit1 Electric Elements and Components Some capacitors look like a cylinder or blob with two wires coming out one end, and are marked to indicate their capacitance (the charge that they store per volt) in microfarads (F), nano

20、farads (nF) or picofarads (pF). Inductance in a circuit is provided by components called inductors, which are almost always built from coils of wire. Large values of inductance are obtained by forming the coil around a magnetic core, such as a lump of iron or ferrite. Inductance is also present in t

21、he windings of electric motors and generators, and to a lesser extent in any piece ofwire. Elements vs. Components There is a distinction between real, physical electrical or electronic components and the ideal electrical elements bywhich they are represented. Electrical elements do not exist physic

22、ally, and are assumed to have ideal properties according to a lumpedelement model. Conversely, components do exist, have less than ideal properties, their values always have a degree of uncertainty, they always include some degree of nonlinearity and typically require a combination of multiple elect

23、ricalelements to approximate their functions.Unit1 Electric Elements and ComponentsNew Words and Expressionscurrentn. 電流 alternating current 交流電流 direct current 直流電流 current density 電流密度 active current 有功電流 reactive current 無功電流voltagen. 電壓 voltage drop 電壓降落 voltage gain 電壓增益 voltage divider 分壓器 vol

24、tage stabilizer 穩(wěn)壓器New Words and Expressionsvariable n. 變量；a.可變的，可調的，易變的 complex variable 復變量 dependent variable 因變量 independent variable 自變量 input variable 輸入變量 charge n. 電荷，充電；v. 充電，帶電，起電 charge distribution 電荷分布 charge particle 帶電粒子 test charge 試驗電荷 positive charge 正電荷 negative charge 負電荷New Word

25、s and Expressionscoulomb n. 庫侖（電荷的單位） coulomb meter 庫侖計circuit n. 電路 circuit diagram 電路圖 analogue circuit 模擬電路 short circuit 短路 open circuit 開路 active circuit 無源電路 passive circuit 無源電路underlying a. 基本的，根本的 潛在的，在下（面）的，下伏的New Words and Expressionsconceptual adj. 概念上的 abstraction n. 抽象lumped element model 集總參數(shù)元件模型 are objects with 傾向于nonlinearity n. 非線性特性 charge n. 電量flux n. 磁通量 ideal current source 理想電流源potential difference 電勢差 ideal voltage source 理想電壓源passive element 無源元件 ohm n. 歐姆resistance n. 電阻 capacitance n. 容量, 電容farad n. 法拉(電容單位) ind