1. Is For Electricity

3. fundamentals that drive our world

5. Charge It!!! What is evidence of charge? What are the two kinds of charge? What are the three ways for and object or material to become charged? HW: Learn 194-201  At least 6 talking to the text points.

6. The Mighty Atom Since there are an equal number of electrons and protons, the net charge on this atom is 0.

7. The Mighty Atom The only way for it to become charged is to gain or lose electrons.

8. Two Types of Charge NEGATIVE (-) : More electrons than protons or an excess of electrons. POSITIVE (+): Fewer electrons than protons or a deficit of electrons. NEUTRAL – Is a state of charge, NOT A TYPE OF CHARGE! Neutral is equal amounts + and -.

9. Quick Check What is the charge on each atom?

10. Charging Can Be Done By.. FRICTION: Rubbing two objects together to remove or deposit electrons. CONTACT: Touching one charged object to a neutral to remove or deposit charge. INDUCTION: Bringing one charged object near a neutral so charges polarize or separate.

11. The Fundamental Concept No matter what – the net charge in any process is always zero. Charge is always conserved. One object might lose charge to another, but the pair of objects still has a net charge of zero.

12. Field of Dreams isn’t about Baseball

13. Sign Convention

14. How Charges Interact

15. How Objects Interact

16. Proof Is In The Pudding

18. Quick Check

19. Insulators Rubbing wool over the R, tape reacted near the R but not near the N. Charge was localized (stuck) near the R and couldn’t move over to the N. N R

20. Conductors

21. The Pie Plates The key to getting a net charge on the pie plate is to touch it so electrons rush from the plate leaving it with a net + charge.

22. Conductors & Insulators CONDUCTORS: Allow charges to pass through them. Induction causes charges to separate. Charges will become evenly distributed on the surface of a conductor.

23. Conductors & Insulators INSULATORS: Do not allow charges to pass through them. Induction causes atoms/molecules to polarize. Charges will become stuck in certain regions of the material.

24. Quick Check

25. Polarization of Insulators

26. Polarization of Conductors

27. Neutrals Will Be Attracted!

28. Quick Check Charged rubber rods are placed near a neutral conducting sphere, causing a redistribution of charge on the spheres. Which of the diagrams below show the proper distribution of charge on the spheres? List all that apply.

29. Charge It! As we have seen that charges behave differently in different materials due to the nature of the bonds involved. Metallic bonds allow electrons to flow freely whereas covalent bonds do not. The dividing line is the metalloids on the Periodic Table. (Thought you were done with chem, eh?!?!)

30. Excuse Me Mr. Coulomb, But Would You Like To Charge That? Like gravity, charges exert forces over a distance. So perhaps we can use gravity as an analog to forces created by charges.

31. Coulomb’s Force Pendulum A positively charged metallic sphere is hung from a non conducting thread. An equally charged negative sphere is brought near by.

32. Coulomb’s Force Pendulum A positively charged metallic sphere is hung from a non conducting thread. An equally charged negative sphere is brought near by. The other sphere shifts towards it. The angle is proportional to the relationship of F e, mg and separation distance r. + mg FeFe θ d

33. Coulomb’s Force Pendulum We know the equation of gravity F = G r mg FeFe θ m 1 m 2 d 2 L d

34. Coulomb’s Force Pendulum Which brings us to this for small angles: We can use similar triangles to relate the two kinds of forces. Fe/d =mg/L Fe/mg = d/L Which says that gravity and the electric force are directly related. r But what about r? mg FeFe θ L d

35. Coulomb’s Force Pendulum

36. Some Simulations http://webphysics.davidson.edu/physlet_resources/bu_s emester2/index.html

37. Coulomb’s Force Pendulum Since they are directly related we conclude both follow the inverse square law. Fe = k r mg FeFe θ L q 1 q 2 r 2

38. Coulomb’s Law Where q is charge measured in coulombs which must be noted as + or - charges r is separation distance in meters k is a constant 9 x 10 9 N·m 2 /C 2 F e = k q 1 q 2 r 2

39. How Big Is A Coulomb? The charge on an electron (e - ) −1.602176487×10 −19 C And a proton (p + ) +1.602176487×10 −19 C It takes 6.2414 ×10 18 electrons to = 1C For singly ionized water that’s.000187 grams Imagine the amount of charge a few grams would hold and you understand a lightning bolt! A mole of e - = 96,484 C. Holy @#&*$!

40. Field of Dreams, Part I Charges and charged objects generate electric fields. These fields can be thought of as vectors passing through empty space. How the field vectors interact is how forces of attraction and repulsion are transferred. We can’t see these fields, only observe their interaction with other objects. Perhaps a look at gravity would help.

41. Electric Field Strength Coulombs Law F g = G Gravity F e = k q 1 q 2 d 2 m 1 m 2 d 2

42. Electric Field Strength Coulombs Law F g = G When these terms are collected we get g the acceleration due to gravity, 9.81 m/s 2 leaving us with the familiar F = mg. F e = k q 1 q 2 d 2 m 1 m 2 d 2

43. Electric Field Strength These terms collect to form a notation of field strength called the Electric Field Intensity, E, which is a vector field, + or -. F = Eq Where E is measured in N/C. F e = k q 1 q 2 d 2

44. Electric Field Notation To note a field we typically show a line (or plate) with a vectors as field lines. +

45. Projectile Motion Link Shoot a charge through the field and it will curve. + -

46. Fields Created By Charges http://www.falstad.com/emstatic/ http://www.falstad.com/vector2de/ http://www.falstad.com/vector3de/

47. Force Related to Distance Lift an object and do work against gravity….. Hey that sounds familiar!!!!!!!!!!! It’s work against gravity, or PE. Wonder if it works for moving a charge in an Electric field?

48. Work Done On Charges PE = mgh E is similar to g h is similar to r or d m is similar to q Bowling Ball

49. Work Done On Charges I can say that I did so many joules of work, total. PE =mgh W = Fd Or I could say I did so many joules of work on the ball. PE = Joules/ BB Bowling Ball

50. Work Done On Charges Each ball has the same PE. The more balls the greater the potential to wreak havoc on the floor. Total PE = 3 x (J/BB) Or 3 J/BB Bowling Ball

51. Work Done On Charges If I imagine that each BB is equal to one coulomb of charge we can write this: PE = J/C Volt = J/C Bowling Ball

52. Work Done On Charges Volt = J/C Which is called POTENTIAL. Bowling Ball

53. A Return to Gravity Coulombs Law F = G F = mg F e = k F = Eq q 1 q 2 d 2 m 1 m 2 d 2

54. Coulombs Law In New Way Fe = k (I) F = Eq E = F/q (II) subbing II into I E = kq/r 2 (III) q 1 q 2 d 2

55. Work Done To Move A Charge http://webphysics.davidson.edu/physlet_resources/bu_s emester2/index.html

56. Work On A Charge W = Fd …………. W = F e d (I) F e = Ed E = F e /q E = k q/r 2 (II) Working a number of substitutions of the these 5 expressions brings some more W = qV V = k q/r