1. Chapter 34 – electric current

3. Charge flows until no difference in potential

4. To sustain flow of charge, something must keep one end at a higher potential

5. Compare this to water flowing from a reservoir

7. Only electrons

8. Variable: I, I = q/t

9. SI unit: ampere (A), the “amp”, 1 A = 1 C / sec

10. The same number of e enter conductor as leave

12. causes a potential difference

13. Must have capacity to maintain

14. constant flow

15. Batteries  chemical reaction

16. Generators  convert mech. work to electrical energy

17. The voltage (potent. diff) is what forces charges to move – “electric pressure”

18. 120 V give 120 J to each coulomb of charge

20. Voltage & resistance (R) – the tendency to slow movement of charges

21. We can ↑ current by either:

22. ↑ voltage (electric pressure) or

23. ↓ resistance (or both)

24. Resistance of conductor depends:

25. Conductivity (how well it conducts)

26. Thickness – thicker = < resistance

27. Length – shorter = < resistance

29. High temp superconductor > 100 K

30. Ohm’s “law” states: current is directly related to voltage and resistance  I = V/R

31. 2 x V = 2 x I, 2 x R = I/2

32. Therefore: small R = large current

34. Depends upon voltage & body resistance

35. Rwith salt water ~ 100 Ω, Rdry ~ 500,000 Ω

36. Voltage drives current: ↑ voltage  ↑ current

37. Touching outlet while dry (120 V)  small current

38. Wet while grounded ↑ current dramatically, poss. Fatal

40. Why birds sit on high voltage wires

41. Charges move down path of least resist. – the wires, not bird

43. To prevent this, a third wire of plug is grounded and connected to appliance

45. Alternating (AC) – charges move back and forth

46. In US, occurs 60 times/sec (60 Hz) at 120 V

47. The wires constantly change polarity

48. Positive ↔ Negative

50. The e experience a force, moving them along E – field

51. Constant collisions (w/ rigid particles of conductor) cause heating & slow the motion of e – drift velocity

53. e do not come from power companies, they are already in the conductors (wires)

54. Power companies provide the energy (via an E-field) that causes the charges to move

56. P = I V

57. Provides a relationship between power & current

58. A kilowatt • hour = energy

59. Energy companies charge some amount per kilowatt • hour