1. Electric Fields and Potentials
Joey Multari, Shannon Burt, Katie Abbott

3. Electric Force Electricity exerts a force similarly to gravity.
Fe = kq1q2 r2
where q1 and q2 represent the amount of charge in Coulombs (6.24 x 1018), r is in meters and k is the electrical constant (9 x 109 Nm2 /C2)
1 Coulomb of electrons travels through a 100-W lightbulb in about one second

5. Review
How many coulombs travel through a 100W light bulb in 3 seconds?
What type of behavior does charge have?
A-Attracting
B-repelling
C-both
D- Fast movement
E- Slow movement
Answer to number one 3
Answer to number two C

6. Electric Fields
Just like gravity field, charges have a force field (E) as well, measured in force per unit charge
E = F = kQ
q r2
where Q is a positive test charge
Direction of fields – away from a positive charge, toward a negative charge

7. Force Field Lines Fields have strength and direction
Field is determined by the force and direction of motion of a positive test charge
Field is strongest where the force is the strongest – where the lines are the most concentrated

18. Electrical Potential
Just like gravity—the potential (possibility) of falling to earth, charges have the potential to move toward or away from each other

19. Electrical Potential
Force of attraction/repulsion causes the potential
Potential is energy divided by charge—since charge is usually small, potential can be relatively large—5000 volts on a charged balloon
A larger amount of charge makes larger potential

20. Voltage – Electrical Potential
Voltage = PE/Q
PE in Joules and Q in Coulombs
100 Volts
J/ C
100-J/ 1-C
1,000,000-J/10,000-C

21. Electric Shielding
Electrons repel toward the outside of any conducting surface
Net charge inside is zero
Electrons flow outward evenly, but pile up on sharp corners
Shielding is important in electronic devices such as televisions and computers

22. Faraday Cage
Faraday stated that the charge on a charged conductor resided only on its exterior
To demonstrate this fact he built a room coated with metal foil, and allowed high-voltage discharges from an electrostatic generator to strike the outside of the room
He used an electroscope to show that there was no excess electric charge on the inside of the room's walls.

24. Person in a car hit by artificial lightning
Person in a car hit by artificial lightning. The lightning strikes the car and jumps to the ground bypassing the front tire arcing from the axle to the ground.

25. Storing Charges
Capacitors can store charges on plates which are separated — as in Franklin’s Leyden jars

26. Storing Charges A capacitor is a device that stores electric charge
A capacitor consists of two conductors separated by an insulator

27. capacitor
capacitor

28. Capacitors and Capacitance
A capacitor in a simple
electric circuit.
Charge Q stored:
The stored charge Q is proportional to the potential difference V between the plates. The capacitance C is the constant of proportionality, measured in Farads.
Farad = Coulomb / Volt

29. Parallel-Plate Capacitor
A simple parallel-plate capacitor consists of two conducting plates of area A separated by a distance d.
Charge +Q is placed on one plate and –Q on the other plate.
An electric field E is created between the plates.

31. Capacitor Applications.
Computer RAM memory and keyboards.
Electronic flashes for cameras.
Electric power surge protectors.
Radios and electronic circuits.
Power supplies

33. Van de Graaf Generator
This machine is capable of producing very high electrostatic potential differences in the order of millions of volts
It works by friction of the belt with the rollers and separates charges at combs which take the charges to the dome and picks them up from the ground at the base

34. Van de Graff Generator

35. Van de Graff Generator

36. Van de Graff Generator

37. Electric Forces and Charges

38. Like Signs Repel

39. Unlike Signs Attract

40. Electrical Force Woman is touching negatively-charge sphere
Electrical force is more powerful than gravity

41. Review Which two signs attract? Which two repel?
A) Unlike signs attract, like signs repel
B) unlike signs repel, like signs attract
C) like signs repel and attract
D) vary depending on amount of charge
E) No charges attract, they only repel
A: Unlike signs attract, like signs repel

42. Conservation of Charge

43. Structure of the Atom
Neutron
Proton
Electron
Energy Levels
or Orbits

44. Charge Electrons and protons have an attribute called charge
Electrons have a negative charge
Protons have a positive charge
1800 times more massive than electrons
Neutrons have no charge

45. Charge Conservation Charge is neither created or destroyed.
What we call charging is either
Transfer of charges, or
Internal rearrangement of charge carrying units
Uncharged (neutral) objects have equal amounts of positive and negative charge
An object with unequal number of electrons and protons is electrically charged
Negative – Electrons > Protons
Positive – Protons > Electrons

46. Removing Electrons from Atoms
Rubber scrapes electrons from fur atoms

47. Charge Quantization
Charge is always an integer multiple of a constant.
Six billion billion electrons is  - 1 Coulomb of charge
Six billion billion proton is + 1 Coulomb of charge
Q=Ne, where e is the unit electrical charge
Electrons have –e charge, protons have +e.
Millikan’s Oil Drop experiment

48. Coulomb’s Law One Coulomb = 6.24 x 1018 electrons
Electrons have a negative charge
qe = -1.6 x Coulomb
Protons have a positive charge
qp = +1.6 x Coulomb
Electrical Force can be positive or negative
Positive – repulsive force
Negative – attractive force

49. Example One pair of charges of 1 C each are 1 m apart F = k q1 q2 / d2
F = (9 x 109 N m2/C2)(1 C)(1 C)/(1-m)2
F = 9 x 109 N m2/C2)(1 C2)/1-m2
F = 9 x 109 N (repulsive)
10 times the weight of a battleship

50. Review
The charge on an electron is 1.6 X 10^-19 C. How many electrons make a charge of 1C?
1/ (1.6 X10^-19) = 6.25 x 10^18

51. What happens to the magnitude of the force as the charges get farther apart?

52. Conductors
An electrical conductor is a substance through which electrical current flows with small resistance
Metals are generally excellent electrical conductors
The electrons in conductors lie in an ‘loose’ outer orbit – the so-called "valence band"

54. Valence Bonds
In a periodic table the columns represent number of valence bonds
Often times, the valence bonds in two combining elements will add up to eight with rare exceptions.

56. Insulators
An electrical insulator is a substance with an extremely high resistance to the flow of charge
Most nonmetals solids are generally excellent insulators
Most atoms hold on to their electrons tightly and are insulators

58. Covalent Bonds
In a tightly knit molecular bond the atoms are held together and therefore hang onto their electrons, creating excellent insulators.

59. Review 1. How much resistance does a conductor have? A- large amount
B- small amount
C- None
D- Average amount
E- infinite
B-Small
columns

60. Review Where are valence electrons represented on the periodic table?
A- columns
B-rows
C- atomic number
D- atomic mass
E- grouping
Answer- a

61. Net Charge Neutral

62. Net Charge Positive

63. Net Charge Negative

64. Charging by Touching
Charging by actually touching object

66. Charging by Induction
Two charged objects placed on opposite sides create a charge in third object.

68. Polarization
Electrons surrounding nucleus may be thought of as a cloud in which the total negative charged is smeared out.

69. Polarization Unpolarized atom
Put negatively charged rod on the right side...
Center of electron cloud shifts to the left.

70. Neutral Objects are Attracted to Charged Objects
Charged comb attracts neutral bits of paper

72. Lightning, lightning rods
Charge Distributions
Charge on Metals
             
              Metal Ball
Charge on Metal Points
                     
           
Lightning, lightning rods

74. Lightning
As the negative charges collect at the bottom of the cloud it forces the negative charges in the ground to be forced away from the surface.  This leaves the ground positive.
A streamer of negative charges is repelled by the bottom of the cloud and attracted by the ground.
As this streamer of negative charges approaches the ground, a streamer of positive charges is repelled by the ground and attracted to the negative streamer.

75. Lightning
When the two streamers connect, they have created a fairly conductive path which allows a sudden down surge of electrons to jump to the ground.  This is the lightning.  
The rapidly moving electrons excite the air along the path so much that it emits light.   It also heats the air so intensely that it rapidly expands creating thunder.
One thing to notice is that the positive charges that make up both the cloud and the ground do not move.  Even the positive streamer launched by the ground is really only made up of positively charged air particles because the electron(s) left the particle.  

77. Electroscope
Conductor
Insulator
Metal Leaves

79. Bibliography
The textbook

80. FIN