A: Electrical Networks
An electrical circuit or network is composed of elements such as resistors, inductors, and capacitors connected together in some manner. If the network contains no energy sources, such as batteries or electrical generators, it is known as a passive network. On the other hand, if one or more energy sources are present, the resultant combination is an active network. In studying the behavior of an electrical network, we are interested in determining the voltages and currents that exist within the circuit. Since a network is composed of passive circuit elements, we must first define the electrical characteristics of these elements.
一个电路由一些元件，如电阻、电感和电容，以某种方式连接组成。如果电路中不包括电源，如电池或者发电机，则称为无源网络。另一方面，如果电路中有一个或多个电源，称为有源网络。在研究电路的行为中，确定存在于电路中的电压和电流是我们感兴趣的。由于一个电路网络由无源元件组成，我们必须首先定义这些元件的电的特性。
In the case of a resistor, the voltage-current relationship is given by Ohm's law, which state
s that the voltage across the resistor is equal to the current through the resistor multiplied by the value of the resistance. Mathematically, this is expressed as
欧姆定律给出了电阻的电压—电流关系：电阻两端的电压等于通过电阻的电流乘以电阻的阻值。其数学表达式为：
The voltage across a pure inductor is defined by Faraday’s law, which states that the voltage across the inductor is proportional to the rate of change with time of the current through the inductor. Thus we have
法拉第定律定义了理想电感两端的电压，指出：电感两端的电压与通过电感的电流的时间变化率成比例关系。因此我们得到以下公式：
The voltage developed across a capacitor is proportional to the electric charge q accumulating on the plates of the capacitor. Since the accumulation of charge may be expressed as the summation, or integral, of the charge increments dq, we have the equation
电容两端产生的电压与积累在电容两极的电荷成比例。由于电荷的积累可以表示为电荷增量的和或积分，我们得到等式。
Active electrical devices involve the conversion of energy to electrical form. For example, the electrical energy in a battery is derived from its stored chemical energy. The electrical energy of a generator is a result of the mechanical energy of the rotating armature.
有源的电设备涉及能量到电的转变。例如，电池中的电能源于它内部储存的化学能。发电机的电能由旋转的电枢的机械能产生。
Active electrical elements occur in two basic forms: voltage sources and current sources. In their ideal form, voltage sources generate a constant voltage independent of the current drawn from the source. The aforementioned battery and generator are regarded as voltage sources since their voltage is essentially constant with load. On the other hand, current sources produce a current whose magnitude is independent of the load connected to the source. Although current sources are not as familiar in practice, the concept does find wide use representing an amplifying device, such as the transistor, by
means of an equivalent electrical circuit.
有源电路元件以两种基本形式出现：电压源和电流源。在理想模型中，电压源产生一个恒值电压，与其产生的电流无关的。前面提到的电池和发电机就属于电压源，因为它们的电压本质上对于负载恒定。另一方面，电流源产生一个电流，其大小与连接的负载无关。虽然电流源在实际应用中并不常见，但其概念广泛用于描述放大装置，如晶体管，通过一个等效电路。
Aconversion翻译方法的定义 common method of analyzing an electrical network is mesh or loop analysis. The fundamental law that is applied in this method is Kirchhoff’s first law, which states that the algebraic sum of the voltages around a closed loop is 0, or, in any closed loop, the sum of the voltage rises must equal the sum of the voltage drops. Mesh analysis consists of assuming that currents-termed loop currents-flow in each loop of a network, algebraically summing the voltage drops around each loop, and setting each sum equal to 0.
分析电路的一个普通方法是网孔或回路分析。应用于这种方法的基本法则是基尔霍夫第一定律，它指出一个封闭回路电压的代数和等于零，或者说，在任意封闭回路中，电压升的
代数和必须等于电压降的代数和。网孔分析包含一个前提条件，即假设流过网络中每一个回路的电流——术语为回路电流，代数求和每一个回路中的电压降，并使每一个和为零。