1. 19 Current, Resistance, & DC Circuits

2. Electric Current Current: net charge passing through a cross-section per unit time. Units: Ampere (A), 1 A = 1C/s (mA,  A, nA, pA) Scalar, Positive current=flowing direction of positive charges

3. Resistance and Ohm’s Law R: resistance, L: length, A:cross section,  : resistivity Unit(R): Ohm(  ), 1  = 1V/A; Unit(  ): ohm.meter ( .m) Temperature dependence: R T = R 0 [1+  (T-T 0 )] T in Celsius, R 0 = R(T=T 0 =20 o C)  : temperature coefficient (0.003~0.005 o C -1 ) L A

4. Resistivities of Different Materials

5. Superconductivity & Non-ohmic Conductors

6. Electromotive Force & Circuits A pump is needed to keep the water circulating  pump~electromotive force (emf) Circulating without pump  No emf~imposiple

7. emf Source (  ) Terminal voltage: V ab =  V ab =  = IR (ideal emf) V ab =  r (with internal resistance, r)

8. Voltage and Current Measurements

9. Potential drops and rises in circuit

10. Power: the energy consumed per unit time. Power Output of a Source Ir 2 is the energy dissipated inside the source  heat Energy and Power in Electric Circuits

11. Resistors in Series & Parallel (in series) (in parallel)

12. Combinations

13. Kirchhoff’s Rules Junction Rule Loop Rule

14. Kirchhoff’s Rules

15. Electrical Measuring Instruments Ammeters Galvanometer Voltmeters

16. Resistance-Capacitance Circuits and Transient Effects

17. Summary: Current

18. Summary: Resistance & Ohm’s Law

19. Summary: emf

20. Summary: Energy & Power

21. Summary: Resistors in Parallel & Series (in series) (in parallel)

22. Summary: Kirchhoff’s Rules

23. Summary: Charging & Discharging

24. Homework Ch19: 1, 5, 7, 12, 24, 31, 33, 42, 48, 52, 57, 61, 63

25. Problem 57

26. Problem 61

27. Problem 52 & 53