KCL, KVL and characteristics of elements are the basis of circuit analysis.
Kirchhoff's Current Laws (KCL)
The algebraic sum代数和 of all the current entering (or leaving) a node is zero, or the sum of all the currents entering a node must equal the sum of all the currents leaving the node.
KCL equation in mathematical form：
sigema ik, k from one to n is zero.
Note: marking assumption(假定)
Generally we assume that if the current is entering the node, its sign is "+(plus)", if leaving, then "-(minus)".
KCL holds to supernode too.KCL对超级节点同样适用
KCL can extend to（扩展到） the appllication in any closed surface闭合面(supernode超级结点) in a circuit, that is, the algebraic sum of currents entering or leaving a closed surface (supernode) is zero.
This law represents a mathematical statement数学描述 of the fact that charge cannot accumulate积累 at a node. A node is not a circuit element and it certainly cannot store, destroy or generate charge.
例句表达
We are required to find or determine the current i1 and current i2 in this circuit.
Solution: We apply KCL to find/determine the current i1 and i2.
First, we will list the corresponding KCL equation for the left node which is minus four plus seven plus i1 is zero. Solving this equation, we can get i1 which equals to minus three amperes.
Kirchhoff's Current Laws (KVL)
The algebraic sum of the voltages around沿着 any loop in a circuit is zero.
Firstly, we need to assume the loop direction: clokwise顺时针 or counterclockwise逆时针
equation：
KVL holds to any loop in space.

for loop1 in space: +V1+V2-Vab=0
KVL can extend to the application in loop in space. In any circuit, the algebraic sum of the voltage around any loop in space is zero.
If the reference direction of a voltage has the same direction as that of the loop, the sign of this voltage in the KVL equations is "+", otherwise（be opposite to the direction）, its sign is "_"
teacher's secret means
1.
2.
利用矢量相加的样貌，但依然按照标量运算
词汇
表明：state
我们要：we are required to do...
求解：find/ determind
应用：apply
相应的：corresponding
重合：coincide
词汇概念
Branch支路：composed of a two-terminal element(外国定义)
国内定义：一条电流
node结点： A point at which two or more elements have in common(外国定义)
国内定义：三支路交点

共两个结点
Path（路径）
Loop（回路）: closed path
Mesh（网孔）: a loop without any other loops inside it
