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4.1 Fields , Circuits And Circuit Parameters
Potential and Potential Difference
Electric charge is as fundamental a constituent of our Universe as the ma and energy.Indeed ,present physical theory supposes that all matter consists of particles ,the principal attributes of which are ma and electric charge .
4.1场，电路和电路参数
势和电位差
电荷是基本的组成为我们的宇宙物质和能量。事实上，目前的物理理论假设，所有的物质粒子组成，其中的主要属性是质量和电荷。
Two kinds of charge are know ,arbitrarily designated positive and negative ,which are characterized by the experimental observation that ,understatic conditions ,separated like charges exert a mutual force of repulsion ,whilst unlike charges ,under similar conditions ,exert a force of attraction .Under these conditions the field of force aociated with charge is referred to as an electric field
两种已知的，被任意指定为正和负的电荷，通过实验观察表现出的特征是，它们在静态条件下，分开的同类电荷受到一个相互排斥的作用力，同时，不同类的电荷，在相同条件下，受到一个吸引的作用力。在这种情况下，与电荷有关的力场被称为电场。
The smallest known charge is that of a single electron, and, since this is much too small to adopt as a unit for all but a few special purposes ,a unit, the COULOMB, equal to 6.24*electrons ,has been chosen as the practiced (S.I.) unit .
已知最小的电荷是单电子，因为单电子太小了而不采用它作为一个单位，除了个别特殊的目的外。所以引用了另一个单位库伦，一库伦等于6.24*个电子。被选为国际标准单位(SI)。
the magnitude of which is dependent upon the charges and their relative positions .As a consequence of their mutual forces, any system of charges poees potential energy, since ,unle constrained ,the individual charges will move and energy will be released.As part of the theoretical structure this energy is ascribed to the electric field, and so it is poible to identify with every point in the field a level of energy
电场力大小取决于电荷之间他们的相对位置。因为是它们相互作用力的结果，任何有电荷的系统都存在电势量，因为，如果没有约束，自由电荷将移动和释放能量。作为理论结构的一部分，这种能量归因于电场。因此可以确定电场中每个点的能量大小。
When one of the charges is of unit magnitude ,and positive, the energy at the point defining its position is referred to as the POTENTIAL at that point ,and hence is measured (in S.I.units) in JOULES per COULOMB(J/C) or VOLTS.The POENTIAL DIFFERENCE between two points in a field is therefore the difference in energy ,per unit charge, at the two points .
一个单位正电荷，在其定义的位置的能量称为在这点的电势，因此测量时用（在国际单位）焦耳每库伦或伏特。因此在电场中两点之间的电势差是指这两点每单位电荷的能量
Observation shows that the force experienced by a charge—measure of the electric field strength—arise with distance and diminishes to zero only at an infinite distance from the source charge (s).Therefore a point at infinity may be considered to be at zero potential .
观测表明，通过测量电场强度的电荷的力随着距离产生然后只在距离源电荷无穷远处减少到零。因此认为在无穷远处的点为零电势。
In practice, however, we are generally concerned with a datum of potential which is not zero—the most common being the earth’s surface considered as an equipotential .Since most of our experiment are earth-bound there is no need to take into account the potential of the earth with respect to the true zero datum .
然而，在现实中，我们研究的对象通常不是零势点，而最常见的是以地球表面作为等势面参考。因为我们
的大多数实验是地球上没有必要考虑地球的电势是否是真正的零电势。
The negative sign means that energy is required from an external source to move the charge from A to B.This energy is recoverable when the charge moves from B to A.Point B is said to be at a higher potential than point负号的意思是外部的能量移动电荷发从a到b所做的功。单电荷从b移动到a的时候这种能量是可恢复的。那么就说b是一个高电势点。
Note that, since energy is scalar, it is not neceary to know the path followed by the charge in paing from A to
B (or from B to A ) nor the law of variation of force with distance over this range.
注意，因为能源是标量，它不需要知道电荷是从A到B的路径（或从B到A的路径）和在这个范围内力的的变化规律。
If ,however, the data were in terms of force at each point of the field, this potential difference would be given by integrating the scalar product of the force (per unit charge)and displacement vectors over the distance AB: 然而，如果数据是根据电场中每一点处的力，那么电势差用ab的距离与单位电荷所受电场力的标量积来表示。
Electric Current
When a charge is in motion relative to a “fixed” frame of reference, an additional force appears to an observer (equipped with a suitable detector) in the fixed frame, this force being referred to as a magnetic force.Analogously, the region of magnetic influence aociated with the moving charge is called a magnetic field, because it has similar characteristics to the field of force of a magnet.It is usual to refer to moving charge by the term ELETRIC CURRENT, the intensity（强度） of which is equal to the time rate of charge transference between two points in a field.
电流
当电荷相对于“固定”的参照物移动，会在固定参照物的观察仪器上产生另一种力（用适当的检测器），这个力被叫为电磁力。类似地，由运动电荷产生磁作用的区域被称为磁场，因为它与磁力场有类似的特征。术语电流通常是指运动的电荷，其强度等于电场中两个点间的单位时间内所通过的电荷。
In consequence, the relation connecting charge and current is:i(t)=dq/dt, where i=current ,and q=charge.因此，电荷与电流的关系为：i(t)=dq/dt,，其中i 指电流，和q指电荷
Unit current, therefore, flows when charge is transferred at the rate of 1 COULOMB/sec, i.e.6.24*electronic charges/sec, this current being designated 1 ampere (1A).It is important to appreciate, however, that when a current be from A to B it is not neceary for every individual charge to move the whole distance AB, but only that the average rate of charge transference should conform to equation i (t).
。
因此，单位电流是指电荷以1库伦每秒即6.24*10的18次方个电子每秒进行移动，这个电流称为1「安培」
（A）。而且，这很好的去说明了，当电流从a流到b时并不需要每个自由电子去从a一直移动到b整段距离，而是只需要考虑电荷移动的平均速度，就能构造i（t）的方程。
The Electric Circuit
These and an other aspects of stationary.moving and accelerating charges are truly encompaed by Maxwell’s electromagnetic theory, but accepting certain restrictions, it is poible to apply a much simplified theory which is sufficiently accurate to describe a wide range of electrical phenomena and applications.Such a theory is referred to as CIRCUIT THEORY and is concerned with the transmiion of energy from one point to another through the use of real devices such as generators wires, batteries, motors and transformers.
电子电路
在这些固定的方面。麦克斯韦电磁理论是讲关于加速移动的电子理论，虽有一定的限制。但可应用于比较简单的实验的理论。足够准确的描述广泛的电现象和应用。这个理论被作为对电路理论和一个点到另一个
点能量传输而言的标准理论。例如电机电线，电池，马达和变压器。
In this proce, interest is focused le upon electric and magnetic fields than upon their circuit equivalents, potentialdifferences and currents.As the above section indicates, the field and circuit concepts are inseparably related, so it is a matter for philosophical argument whether energy transfer is effected by fields or by voltages and currents.Neverthele, the usefulne of the circuit concept lies in the relatively simple solution of such problems which it permits.
在这个过程中，主要集中电场和磁场和他们电路的电位差电流有密切的关系，正如上面所说，电场与电路是密不可分的。能量的转换是通过电场改变电压，电流而改变的。这是一个科学的观点也存在问题他只适用于简单的电路。
The transformation from field to circuit conceptualization consists in regarding currents as flowing from one physical device to another only through wires, which connect them together, and the characteristics of each device as being purely local; that is to say, the currents may be constant or time-dependent but not dependent on space coordinates in the circuit.Such a circuit is said to consist of lumped (rather than distributed) elements, and the restriction imply that only conduction currents are considered and that displacement currents are not.
从现场的概念转化为电路中包括关于为流动从一台物理设备到另一只通过导线，电流，连接在一起，并作为being纯粹的每个设备的local characteristics，这是对say，may be的currents常数或时间依赖性，但不依赖于空间坐标的电路。这种电路可分为集中（而不是分散）等元素的限制意味着，只有传导电流，位移电流考虑是不是。
Conduction currents flow particularly easily in most metals, this property being due to the extremely large number of free electrons available as charge carriers in the crystal lattice.Thus, at normal temperatures, silver is the best of all conductors, with copper and aluminum only slightly inferior.
传导电流的流动，特别是在大多数金属容易，此属性是由于自由电子在晶格中电荷的数量极其庞大的。因此，在正常温度下，银是最好的所有导体，与只有稍差的铜和铝。
Drift velocity is, under normal conditions of temperature, a much larger but random thermal agitation velocity which, since it does not contribute to the net transference of charge, is of no concern in the macroscopic view of current adopted here.
The eential part of an electric circuit consists in its simplest form, of an energy source and an interconnected energy diipation or conversion device, known as the load.
漂移速度是，在正常条件下的温度，一个更大的，但随机热搅拌速度，因为它没有贡献的净转移的电荷，是不关心在这里通过的电流的宏观图。
的电路的主要部分的包括在其最简单的形式中，能量源和一个相互关联的能量耗散或转换装置的，被称为负载。
practical energy source may take one of many Energy Source
A forms, depending, for example, on electro-chemical, electromagnetic, thermo-electric, photo-electric, etc.., principle, but for the purpose of circuit analysis only two idealized form are recognized, to one of which all practical sources approximate.These are: 1 the voltage source and 2 the current source.
实际的能源来源可以采取许多能源来源之一
一个形式，这取决于例如，在电化学，电磁，热，电，光电等。，原则，但对于只有两个电路分析的目的是公认的理想形式，其中之一便是一切可行的来源近似。它们是：1，电压源和电流源2。
The voltage source maintains a constant terminal voltage irrespective of the current supplied to the load.It is important to appreciate that the voltage may be afunction of, for example, time, temperature, preure, etc.; it is constant only with respect to variations of load.
电压源的端电压保持恒定的，不论对当前提供给负载。重要的是要明白，电压可能是一个函数关于，例如，时间，温度，压力等，它是恒定的只考虑负载的变化。
The current source maintains a constant current in the load irrespective of the terminal voltage-which, in the case, is determined by the magnitude of the load.As with the voltage source, the generated current may depend on many other factors, but its one eential attribute is its independence of load.
电流源保持恒定的电流在负载里，不论末端电压如何，既然这样，是由负载的大小决定的。与电压源一样，生成的电流可能取决于其他许多因素，但其本质属性是它独立负载。
Power and Energy
The definitions of potential and potential difference lead to the following relationships: the energy, w, expanded in moving a charge q through a potential difference (p.d.) v is given by: w= qv, hence,dw/dt=v*dq/dt=vi .
The rate of expenditure of energy is define as the power p.Hence, in general the power is givens by p(t)=v(t)*i(t) and is measured in WATTS when v and I are in volts and amperes, respectively.
If power p(t) is expended for time T, the total energy expended (or stored) is :
电力和能源
潜在的定义和潜在的差异导致的以下几个关系：能源，功，动议通过电位差（PD）的V是给予一个电荷q扩大为：w= qv，因此，dw/dt=v*dq/dt=vi。
对能量消耗率定义为权力页因此，在一般的权力是由P吉文斯（吨）=五（吨）*我（吨），并以瓦时测v和我为伏特和安培，分别。
如果功率P（t）是为时间T，总能量消耗（或存储）花费是：
The load
By a method similar to that adopted for energy sources, the load-or paive element of a circuit--- may be idealized and defined by its terminal voltage/current relationship.All practical paive devices poe energy diipative properties, often accompanied by energy-storage properties so that three distinct idealized types are poible.
负载
通过类似的方法，对能源通过负载或电路---可能是理想化，其端点电压/电流关系因素。所有实际的被动设备具有能量耗散属性,常伴有储能属性,这样三个不同的理想化的类型是可能的。
1.The resistance parameter
A circuit which diipates energy but stores none is said to consist solely of resistance.The property is defined by the relationship: R=v(t)/i(t), where R is the resistance in OHMS if v(t) and i(t) are volts and amperes, respectively, and this equation is known as Ohm’s Law.
1，电阻参数
一个电路只消耗能量而不储存能量，那只含有电阻。该属性由关系式R=v(t)/i(t)定义的，如果V（t）和i（t）的单位分别是伏特和安培，那么R的单位为欧姆，这个公式被称为欧姆定律。
The corresponding diagrammatic representation is shown in Figure 4.2(a) which also shows the positive directions of p.d.and current.It should be noted that, unlike an active element, a paive element develops a potential difference in opposition to the current flow so that there is a fall of potential through the element in the direction of the current flow.
相应的图解见图4.2（1）该表注明了电流和电势差的正方向。应当指出的是，不同于有源元件，无源元件是与电流流向相反产生电位差的，使得无源元件中电势是随着电流的流向逐降低的。
For this reason the terminal p.d.is called a potential drop or voltage drop.The element which poees resistance is termed is a resistor.由于这个原因，端电压称为一个电势的下降或电压下降。具有电阻的元件被称为是一个电阻器。
The reciprocal of resistance is conductance designated by the symbol G.Thus, G=1/R, the units of G being siemens, or reciprocal ohms.Hence, an alternative form of Ohm’s Law is: i(t)=v(t)G.电阻的倒数为电导，用符号G
的表示，因此，G=1 / R，G的单位是西门子，或欧姆的倒数。因此，另一种形式的欧姆定律是：I（T）= V（T）G
The Power diipated, v(t) i(t) ,may be written in terms of resistance (or conductance) and voltage or current only; thus,
因此，功率，v(t) i(t)，也可以只用电流或者电压中一个来和由电阻（电导）组合表示.：
2.The Inductance Parameter
A circuit is said to poe inductance if it is able to store magnetic field energy.The property is defined by the relationship v(t)=L*di(t)/d(t), where L is the inductance, the units of which are HENRYS if v and I are in volts and amperes, respectively, and t is in seconds.A p.d.of 1 V will, therefore, cause the current to change at the rate of 1 A/sec in an inductance of 1H.The circuit representation of the inductance parameter is shown in Figure 4.2(b).2，电感参数
如果一个电路是能够存储磁场能量，则这个电路是感性电路，。该性质是由v(t)=L*di(t)/d(t)定义的，其中L是电感，单位是亨利,电压的单位是伏特,电流的单位是安培，时间单位是秒。因此，1 V可导致电流变化率1A / 1秒的1H电感。该电感参数电路如图所示代表4.2（b）项。
Equation may also be written in general integral form:
The element which poees inductance is termed an inductor.
And the power, v(t) i(t), may be writen: p(t)=L*I(t)*di(t)/dt, and is non-zero only when di(t)/dt has a value.Hence for a steady current i(t)=I, p(t)=0, but for the current I to have been established, p(t) has contributed to the stored energy:where T is the time taken for the current to build up to I.
公式也可以写成一般积分形式：
拥有的元素被称为电感的电感。
功率，电压电流，可写：p(t)=L*I(t)*di(t)/dt,，di(t)/dt不等于零，有一个值。因此，对于一个稳定的电流i（t）=I，p(t)=0，但对目前我已经确定，功率有助于储存能量，其中T是所用的时间，I是电流。
3.The capacitance parameter 3。电容参数
A circuit which is able to store electrostatic field energy is said to poe capacitance.The property is defined in terms of the electric charge stored per unit of potential difference at its terminals, according to the equation: q(t)=Cv(t), where C is the capacitance, the units of which are FARADS when v and q are in volts and coulombs, respectively.Hence, a capacitance of 1 F stores a charge of 1C for a terminal p.d.of 1V.Combining equations gives: I(t)=C dv(t)/dt with t in seconds.一个电路能够存储静电场能量便是具有容性。性质由其端子在电荷存储每单位电势定义的，其根据公式：q(t)=Cv(t)，当v和Q分别是伏特和库时，其中C是电容，单位是法拉，。因此，一个1F电容存储1C的电荷时末端电势1V。结合方程可得：I(t)=C dv(t)/dt，时间电位是秒。
Thus, a current of 1A flows into a capacitance of 1 F when the terminal voltage changes at the rate of 1V/sec.
因此， 1A电流流入1 F的电容时，端电压变化率为1V/sec。
And the equation may be rewritten in general integral form :
而方程可重写为一般积分形式：
The element which poees capacitance is termed a capacitor, and its circuit representation is illustrated in Figure 4.2.(c).该元素具有电容被称为一个电容器，其电路图说明如图4.2。
The power,v(t)i(t) , may be written: p(t)=C*v(t)*dv(t)/dt and is non-zero only when dv(t)/dt has a value.Hence, for a steady voltage v(t)=V, say, p(t)=0,but for the voltage V to have built up on the capacitor, p(t) has contributed to the stored energy,where T is the time taken for the voltage to have built up to V.
功率，v(t)i(t)，可写为：p(t)=C*v(t)*dv(t)/dt，当dv(t)/dt不等于零时才有意义。因此，对于一个稳定电压v(t)=V，
表示p(t)=0 ，但对有电压V的电容器，功率有助于储存能量，其中T是所用的时间，V是电压。
Equations v(t)= L*di(t)/dt and I(t)=C*dv(t)/dt show that step discontinuities are not poible in the current through inductance nor in the voltage acro capacitance, since such steps would require, respectively, infinite voltage and infinite current.The ideas implicit in these restrictions are important in the analysis of circuits containing inductance and capacitance since they enable the initial conditions to be defined .
方程v(t)= L*di(t)/dt和I(t)=C*dv(t)/dt显示，步骤不连续电流是不可能通过电感或电压储在电容，由于这样的步骤分别需要无限大的电压和无限大的电流。在这限制的条件下，对电感和电容的电路的分析是重要的，因为这是定义它们的初始条件
