Notes to the text
1.One of the most fundamental concepts in electric circuit analysis電路分析中最基本的概念之一
2.but external to the device we typically concentrate on the electrons which flow through the connecting wires但是，對于器件的外部我們特別關注流經連接導線的電子
3.by counting the total charge that passes through an arbitrary cross section of a wire during an interval of one second計算一秒時間間隔內通過導線任意橫切面的總電荷
4.A quantity of charge that does not change with time不隨時間變化的電荷數量
5.The instantaneous amount of charge電荷瞬時總量
6.Thus，a constant charge may be represented by either Q or q，but an amount of charge that changes over time must be represented by the lowercase letter q. 于是，常量電荷可以用Q或q表示，但是隨時間變化的電荷量必須用小寫字母q表示。
7.The idea of"transfer of charge"or"charge in motion"is of vital importance to us in studying electric circuits“電荷轉移”或“電荷運動”對我們研究電路是非常重要的
8. The familiar cross-country power-transmission line is a practical example of a device that transfers energy. 我們熟悉的橫越國家的電源傳輸線就是傳輸能量的器件的一個實際例子。
9.Of equal importance is the possibility of varying the rate at which the charge is transferred in order to communicate or transfer information. 同樣重要的是（為了進行通信或傳輸信息）改變電荷傳輸速率的可能性。
10.The current present in a discrete path，such as a metallic wire，has both a numerical value and a direction associated with it;it is a measure of the rate at which charge is moving past a given reference point in a specified direction. 呈現在離散電路（如金屬導線）中的電流既有和它相關聯的數值又有方向，它是電荷按指定方向通過某給定參考點的速率的度量。
11.the total charge that has passed the reference point since an arbitrary time t=0，moving in the defined direction從任意時間t=0起，按定義方向運動通過參考點的總電荷12.A contribution to this total charge這個總電荷的作用
13.the instantaneous rate at which net positive charge is moving past that point in the specified direction凈正電荷按指定方向移動通過該點的瞬時速率
14.A current that is constant in time時間為常量的電流
15.currents that vary sinusoidally with time隨時間按正弦變化的電流
16.Such a current is often referred to as alternating current. 這種電流常稱為交流電。
17.We establish a graphical symbol for current by placing an arrow next to the conductor. 我們放置一個箭頭在導體的旁邊來建立電流的圖形符號。
18.All four statements and both figures represent currents that are equivalent in their electrical effects，and we say that they are equal. 四種陳述及兩個圖形描述了電氣效果相等的電流，于是我們稱它們等效。
19.Thus，any definition of current can agree with the physical nature of conduction only part of the time. 因此，電流的定義只有部分時候與導電器件的物理特性相一致。
20.It is essential that we realize that the current arrow does not indicate the"actual"direction of current flow but is simply part of a convention that allows us to talk about "the current in the wire" in an unambiguous manner. 電流的箭頭并不表示電流的實際方向，它僅僅是允許我們以清晰的方式談論導線中的電流的約定部分，認識到這一點是非常重要的。
21.We must now begin to refer to a circuit element，something best defined in general terms to begin with. 我們現在必須開始引入電路元件這種用一般術語定義了的東西（元件）作為開始。
22.can be represented by combinations of simple circuit elements能夠用簡單的電路元件的組合來表示
23.We begin by showing a very general circuit element as a shapeless object possessing two terminals at which connections to other elements may be made. 我們通過顯示一個非常普通的（具有兩個與其他元件連接的端的無形狀物體）元件作為開始。
24.by describing the electrical characteristics that may be observed at their terminals通過描述在它們的端點能觀察到的電氣特性
25.Let us also assume that pushing charge through the element requires an expenditure of energy. 讓我們還假定推動電荷通過元件需要消耗能量。
26.Thus，the voltage across a terminal pair is a measure of the work required to move charge through the element. 于是，一對端點之間的電壓就是移動電荷通過元件所需的功的度量。
27.According to the principle of conservation of energy，the energy that is expended in forcing charge through the element must appear somewhere else. 根據能量守恒原理，使電荷通過元件所耗費的能量肯定會出現在別的地方。
28.We must now establish a convention by which we can distinguish between energy supplied to an element，and energy that is supplied by the element itself. 我們現在必須建立一個約定，由這個約定我們能夠區分供給元件的能量及元件自己提供的能量。