1. Electrostatics

2. Section 1: Intro to Static Electricity

3. Define Electrostatics
Electrostatics- Physics that deals with the attractions and repulsions of electrical charges not dependent on their motion. (Electricity at rest)

4. Electrical forces arise from charged particles in the atoms.
What are the charged particles called?
- ____________
+ ____________

5. Electrical forces arise from charged particles in the atoms.
Proton (+)
Electron (-)

6. Define Charge
Charge- The fundamental electrical property to which mutual attractions or repulsions between electrons or protons is attributed.
Neutral atoms contain equal numbers of positive protons and negative electrons. (net 0 charge)

7. Only the electrons move to create unbalanced charges.

8. When atoms lose electrons they become positively charged ions.
Becomes
Neutral Sodium (Na)
11 protons(+) and 11 electrons(-)
Positive Sodium Ion (Na+)
11 protons(+) and 10 electrons(-)

9. When atoms gain electrons they become negatively charged ions.
17 p
18 n
17 p
18 n
Becomes
Neutral Chlorine (Cl)
17 protons(+) and 17 electrons(-)
Negative Chlorine Ion (Cl-)
17 protons(+) and 18 electrons(-)

10. Electrical charges are conserved!
When one atom becomes a positive ion another one/few must have accepted those electrons and become equally negative
Ex sodium is +1 because it gave its extra electron to chlorine
17 p
18 n
11p
12 n
Becomes Negative Chlorine Ion (Cl-)
17 protons(+) and 18 electrons(-)
Becomes Positive Sodium Ion (Na+)
11 protons(+) and 10 electrons(-)

11. Interaction between charges
Like charges repel and opposite charges attract.

12. Define Static Electricity
Static Electricity - Electricity at rest
Electric charges that can be confined to an object
I hate static electricity

13. Some materials have a greater affinity for electrons
Greater affinity for e- : stick to electrons more and tend to gain electrons becoming negative
Less affinity for e- : don’t hold electrons as tight and are more likely to loose electrons become positive

14. Friction can cause charge separation
Electrons are stripped from one material and added to the other when rubbed together

15. A wool cloth does not have much affinity for electrons.
Charging by Friction
A wool cloth does not have much affinity for electrons.
Becomes Positive
PVC becomes negative

16. Activity 1 List some examples of charging by friction
When have you noticed static electricity or attraction of one object to another
Static cling from dryer (cotton socks w/ nylon pants)
Balloon rubbed in hair
Walking on carpet

17. Attraction for electrons
(Hold electrons tightly)
Most likely to gain electrons and become negative
(Hold electrons loosely)
Most likely to loose electrons and become positive)
PVC
Rubber
Cotton
Paper
Silk
Fur
Wool
Nylon
Hair
Acetate
Glass

18. Question Set 1
1. A girl pulls a wool cap off her head. What charge will be produced:
on her hair?
on her cap?
2. Which will produce the most static cling with a cotton t-shirt in a dryer. Wool socks or a nylon nightgown?
3. Can there be static cling if only cotton items are placed in a dryer?
4. Predict the charges on the underlined objects:
A rubber rod rubbed with fur
A glass test tube rubbed with silk
A PVC pipe rubbed with nylon

19. Question Set 1
1. A girl pulls a wool cap off her head. What charge will be produced:
on her hair? positive
on her cap? negative
2. Which will produce the most static cling with a cotton t-shirt in a dryer. Wool socks or a nylon nightgown? Nylon
3. Can there be static cling if only cotton items are placed in a dryer? No
4. Predict the charges on the underlined objects:
A rubber rod rubbed with fur negative
A glass test tube rubbed with silk positive
A PVC pipe rubbed with nylon negative

20. Conductor: Material through which electrons move freely
Examples (gold, silver, copper, and aluminum)
The general rule is that good thermo conductors are good electric conductors

21. Metals tend to share electrons in electron clouds
electrons are free to move around making them better conductors.

22. Electrical Insulator
Electrical Conductor

23. Insulator: Material through which electrons do not freely move
Examples: rubber, paper, plastic, air

24. Grounding Removing a static charge by producing a path to the ground
Electrons move from a negatively charged objects to the ground until the object is neutral
Electrons move from ground to neutralize positively charged objects
The earth both accepts and gives electrons while remaining overall neutral
Grounding wand for Van De Graaff generator

25. Grounding
It’s easy to ground conductors since electrons transfer readily
It’s hard to ground insulators since charges don’t move away easily

26. Section 2: Charging Objects
Three Ways of putting a charge on an object
Friction
Induction
Conduction

27. 1. Charging by Friction
Charging by rubbing objects that have different affinities for electrons together

28. Induction (charging without contact)
Bring a charged object (rod) close to a neutral one (ball) without contact

29. Induction (charging without contact)
Bring a charged object (rod) close to a neutral one (ball) without contact
The electrons in the ball will be repelled leaving a positive side
- - -

30. Induction (charging without contact)
Bring a charged object (rod) close to a neutral one (ball) without contact
The electrons in the ball will be repelled leaving a positive side
The now positive sided ball with be attracted to the negative rod
- - -

31. Induction (charging without contact)
Induction is only a temporary change without contact therefore electrons are not transferred
The charge induced is opposite
Take away the rod and a neutral charge will return
- - -

32. Conduction (charging with contact)
Conduction is a more permanent change with contact; electrons are transferred and then isolated.
Charge conducted is the same
After conduction the ball and rod will repel each other
- - -

33. Make this table in your notes
Conduction
Induction
Contact?
Contact
No Contact
Permanent?
Permanent
Temporary
Charge vs. Charging Device
Same
Opposite

34. Section 3: Coulomb’s Law

35. Electric Charge Symbol is Q or q The MKS unit is the coulomb (C)
1 C = the charge on 6.25 x 1018 electrons
Extra info to help you with problems
1 electron = 1.60 x C
A coulomb is a huge charge. Static charge is usually stated in µC which is 1x10-6 C.

36. Magnitude of force
3 factors affecting the magnitude of the force between two charged objects:
Charge on the objects
Distance between objects
Material separating objects

37. Coulomb’s Law F: electrical force Q1: charge 1 Q2: charge 2
F: electrical force
Q1: charge 1
Q2: charge 2
d: distance between charges
k: constant depending on materials separating objects
For air, k = 8.99 x 109 N·m2/C2

38. When using this equation:
A positive force (F) signifies repulsion
Both charges (Qs) must be positive or both negative
A negative force (F) signifies attraction
One charge (Q1 or Q2) must be positive and the other negative

39. Example 1
a. What is the electrostatic force between two objects, +13 μC and -22 μC which are 0.055m apart (μC = x 10-6 C)
b. Is it an attraction or a repulsion?

40. Example 1
a. What is the electrostatic force between two objects, +13 μC and -22 μC which are 0.055m apart (μC = x 10-6 C)
b. Is it an attraction or a repulsion?
Attraction (Q1 and Q2 are opposite signs)

41. Coulomb’s Law is similar to Newton’s Law of Gravity Similarities: el
Coulomb’s Law is similar to Newton’s Law of Gravity
Similarities:
They both are used to calculate a field force
Both forces have an inverse square relationship to distance
They are both related by a constant
Differences:
Force of gravity is always attractive
Electrostatic force can be either attractive or repulsive
Gravities constant is very small since gravity is a very weak force
Fg relates force created by a masses, Fel relates force created by charges

42. el
Both electric and gravitational forces are field forces because objects do not have to touch to be subjected to the force.

43. Section 4: Electrical Fields
Electrical Field (E): an area of electrical influence around a charged object.
Variable E
Unit: newton per coulomb (N/C)

44. Drawing electrical fields-
Arrows point away from the positive and toward the negative
In the direction a positive charge would travel in the field
Spacing of lines show field strength

45. Drawing electrical fields-
Arrows point away from the positive and toward the negative
In the direction a positive charge would travel in the field
Spacing of lines show field strength
This is what it would be seen if you used iron filings to see the field

46. Common point charge examples

48. Electric field between two parallel plates

49. All charge lies on the surface of a conductor
Electrical field inside a conductor is zero
E = 0 inside conductor

50. True or false: A cars tires protect you from being struck by lightning

51. False: Electrical shielding does
The metal outside the car gives the car a path to the ground

52. Shielding
Here is more proof of shielding

53. Section 5: Voltage

54. I.
Work must be done on a positive charge to move it away from a negative sphere.
The electric PE of the charge will increase

55. When the charge is released, it will move closer to the negative sphere. Its electric PE will decrease and work can be done by the charge.

56. II.
Work is required to push the small + charge against the electric field around the + sphere.
Since work is done on the small charge, its PE increases.
The closer it gets, the more it is repelled by the field and the more work is required.

57. III.
Once the little charge is placed on the sphere, the charge on the sphere increases, and the field around it becomes stronger.
Moving the next + charge toward the sphere will take even more work and give the small charge more PE.

58. Potential Difference (Electric Potential)
Potential difference (or electrical potential) is work done as a single charge is moved in an electric field.
Unit is the volt
1V = 1J/1C
Potential difference is measured in volts and commonly called voltage (V).

59. Which positive charge has more potential energy?

60. Which positive charge has more potential energy?
Its closer and therefore
has a greater repulsion

61. Activity 2 Which rock has more potential energy?
Which rock has a greater potential difference? A B

62. Rock B has more charges and therefore more potential energy (PE)
Both rocks have the same potential difference (potential energy per charge)
but
Rock B has more charges and therefore more potential energy (PE) A B

63. Electric potential is not the same as electrical potential energy
Electric potential is not the same as electrical potential energy. Electric potential is electric potential energy per charge.
Potential Energy (PE Total)
Electric Potential (PE of one charge)

64. Section 6: Electric Storage and Discharge

65. Electrical Energy Storage
Capacitor- simple device used to store electrical energy. The simplest form is a pair of conducting plates separated by a small distance.
The plates hole equal and opposite charges
The electrical energy in a capacitor comes from the work done to charge it.
These capacitors consist of thin metal foils rolled up into a cylinder

66. Electric Discharge
Discharge occurs when the electric field around a conductor becomes so strong. The air is ionized helping the charge make a break for the ground.

67. Arc Discharge
Arc- a rapid discharge producing heat, light, and sound.

68. Lightning 1 2
Storm clouds cause a separation of charges trough updrafts and downdrafts. The bottoms of clouds become negative.
The negative bottom of the clouds induces the top of the ground to become positive
Moist air is ionized by the strong electrical field creating a conducting path. Lightning is the arc formed. 3

69. Facts about lightning
Charges are separated in storm clouds; + top and – bottom
Ground under the cloud becomes positively charged by induction
V = millions of volts; causes arc discharge with tremendous energy.

70. Corona Discharge
Corona- a slow discharge of static electricity from a pointed conductor

71. Lightning Rods-
Prevent strike by allowing induced charge to leak off building in a corona discharge
Provide a path to the ground in case of a strike