高职电气自动化专业英语1公开课.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 1 Electric and Electronic Technology Fundamentals,Unit 1 Electric Elements and Components,Text,New Words and Expressions,Exercises,End,Unit1 Electric Elements and Components,Introduction,Electrical elements are conceptual abstractions used in the analysis of electrical networks.Any electrical 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 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 of,multiple electrical elements in order to approximate its,functions.,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.,Unit1 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:,Current 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 source,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 ohms-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 the,Unit1 Electric Elements and Components,The Components,A battery provides electromotive 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 the 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 voltage,source.,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 wire 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 variable current source that is,controlled 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 colored 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 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 higher when it is hot,than 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,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 platesthe,capacitor is then said to be discharged.,Unit1 Electric Elements and Components,Unit1 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),nanofarads(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 the windings of electric motors and generators,and to a lesser extent in any piece of,wire.,Elements vs.Components,There is a distinction between real,physical electrical or electronic components and the ideal electrical elements by,which they are represented.,Electrical elements do not exist physically,and are assumed to have ideal properties according to a lumped,element 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 electrical,elements to approximate their functions.,Unit1 Electric Elements and Components,New Words and Expressions,current,n.,电流,alternating current,交流电流,direct current,直流电流,current density,电流密度,active current,有功电流,reactive current,无功电流,voltage,n.电压,voltage drop,电压降落,voltage gain,电压增益,voltage divider,分压器,voltage stabilizer,稳压器,New Words and Expressions,variable,n.变量；a.可变的，可调的，易变的,complex variable,复变量,dependent variable,因变量,independent variable,自变量,input variable,输入变量,charge,n.电荷，充电；v.充电，带电，起电,charge distribution,电荷分布,charge particle,带电粒子,test charge,试验电荷,positive charge,正电荷,negative charge,负电荷,New Words and Expressions,coulomb,n.库仑（电荷的单位）,coulomb meter,库仑计,circuit,n.电路,circuit diagram,电路图,analogue circuit,模拟电路,short circuit,短路,open circuit,开路,active circuit,无源电路,passive circuit,无源电路,underlying,a.基本的，根本的 潜在的，在下（面）的，下伏的,New Words and Expressions,conceptual,adj.概念上的,abstraction,n.抽象,lumped element model,集总参数元件模型,are objects with,倾向于,nonlinearity,n.非线性特性,charge,n.电量,flux,n.磁通量,ideal current source,理想电流源,potential difference,电势差,ideal voltage source,理想电压源,passive element,无源元件,ohm,n.欧姆,resistance,n.电阻,capacitance,n.容量,电容,farad,n.法拉(电容单位),inductance,n.电感,henries,n.亨利(电感单位),electromotive force,电动势,negative pole,负极,positive pole,正极,exhaust,vt.用尽,耗尽,cylinde,r n.圆柱体,graphite,n.石墨,colored stripe,色环,tolerance,n.额定容量,filament,n.金属丝,withstand,vt.抵挡,经受住,capacito,r n.电容器,nanofarad,n.微法(拉),picofarad,n.皮法拉,inductor,n.感应器,lump,n.块(尤指小块),ferrite,n.铁氧体,Return,Exercises,I.Mark the follow statements with T or F according to the text.,There isnt a distinction between real,physical electrical or electronic components and the ideal electrical elements by which they are represented.,(),Components do exist,have some ideal properties.,(),Voltage source,measured in voltsproduces a potential difference between two points.(),Each electrical element affects the voltage in network or current through the network in a particular way.(),Current sources are more often used when representing conductors.,(),Exercises,.Complete the following sentences.,1.The concept of _ is used in the analysis of,_.,2.Each electrical element affects the _ in the network or _through the network in particular way.,3.Resistance R,measured in _ produces a voltage,_ the current following through it.,4.On a first degree of approximation,a bipolar transistor may be represented by a _ that is control by the,_.,5.A network is a connection of _ or _ components,and may not necessarily be a _.,Unit 1,End,