1. 2.1 Ohm's Law 2.3 Resistors Combinations 2.2 Kirchhoff's Laws Chapter 2 Basic Laws 基本定律

2. 2.1 Ohm’s Law 欧姆定律 + - v i R Ohm's law states that the voltage v across a resistor is directly proportional to the current i flowing through the resistor. （欧姆） resistor resistance 电阻（名称） 电阻值 Pay attention:

3. A short circuit is a circuit element with resistance approaching zero. A short circuit (R = 0) R =0 i v=0 Network Short Circuit: 短路

4. An open circuit is a circuit element with resistance approaching infinity （无限大）. An open circuit (R=  ) R=R=R=R= i =0 v Network Open Circuit : 开路

5. v i 0 Slope=R v i 0 The v~i characteristic （电压 ~ 电流特性） of : (a) a linear resistor, (b) a nonlinear resistor.

6. NOTE : 1. The power is nonlinear function of either current or voltage. Conductance (G) （电导） The power can be expressed in terms of R. S ( 西门子） （姆欧） 2. A resistor always absorbs power （吸收功率） from the circuit. A resistor is a passive element.

7. Ⅰ. Nodes, Branches and Loops 结点，支路和回路 Independent loops ( 独立的回路数 ) A branch represents a single element such as a voltage source or a resistor. A node is the point of connection between two or more branches. A loop is any closed path in a circuit. A mesh ( 网孔） is a loop that contains no other loops within it. Independent nodes ( 独立的结点数 ) : n-1 1 2 3 4 2.2 Kirchhoff‘s Laws 基尔霍夫定律

8. b=? n=? l=? b=5 n=3 l=b-n+1=3

9. Ⅱ. Kirchhoff‘s Laws 基尔霍夫定律 Kirchhoff’s current law states that the algebraic sum of currents entering a node (or a closed boundary) is zero. Kirchhoff’s current lawKCLKirchhoff’s current law （ KCL 基尔霍夫电流定律）

10. The sum of the currents entering a node is equal to the sum of the currents leaving the node. or

11. Kirchhoff ’ s voltage law states that the algebraic sum of voltages around a closed path (or loop) is zero. Kirchhoff’s voltage lawKVLKirchhoff’s voltage law （ KVL 基尔霍夫电压定律）

12. or Sum of voltage drops=Sum of voltage rises

13. Example 2.1 Calculate the current i in the circuit Solution: For loop 1, KVL gives For loop 2: KVL gives At node 1 : then i1i1 i2i2 loop1 loop2 2 1

14. Ⅰ. Series Resistors and Voltage Division For N resistors in series The equivalent resistance of any number of resistors connected in series is the sum of the individual resistances. 2.3 Resistors Combinations 串联电阻和分压

15. voltage division （分压） Then

16. Ⅱ. Parallel Resistors and Current Division 并联电阻和分流 The equivalent resistance of N resistors connected in parallel:

17. The equivalent conductance of resistors connected in parallel is the sum of their individual conductances.

18. Two resistors in parallel current division （分流）

19. Ⅲ. Wye-Delta Transformations Y-  转换 Balanced Wye-Delta Transformations

20. 部分电路图和内容参考了： 电路基础（第 3 版），清华大学出版社 电路（第 5 版），高等教育出版社 特此感谢！