1. Electrostatics

2. What is this substance?

3. Thales of Miletos (600 BC)
discovered that if he rubbed fur
on amber, the amber would
attract feathers. This was referred
to as the “Amber Effect”

4. History
The word electricity comes from the Greek elektron which means “amber”.
The “amber effect” is what we call static electricity. 4

5. ELECTROSTATICS the study of electric charges, forces and fields
Static Electricity is “Stationary Electricity” or Accumulation of charge

6. History Two types of charges exists, arbitrarily named
POSITIVE and NEGATIVE
By Benjamin Franklin
So what is positive and what is negative?

7. We know that charged particles exist in atoms
Electrons are responsible for negative charge
and Protons for positive charge
Benjamin Franklin did not know about the existence of these particles but, he did investigate the behavior of static discharge and lightning.

8. Ben knew that if certain electrically neutral objects are rubbed, they can become charged.
For example; when rubber is rubbed with a wool cloth, both become charged.
or a comb through hair
The rubber scrapes electrons from fur atoms. So the rubber is negatively charged and the cloth is positively charged.

9. Ben also knew that a charge separation occurs when a glass rod is rubbed with a silk cloth
In the case of the glass and silk, the glass rod loses negative charge and becomes positively charged while the silk cloth gains negative charge and therefore becomes negatively charged.

10. like charged object repel and unlike charges attract
Ben experimented with the interactions between the charge objects. He suspended one and brought other charged objects near…
repel
repel
attract
Electrons:
Ben observed that
like charged object repel
and unlike charges attract

11. Fundamental Rule Opposites attract, Likes Repel
Things don’t like having a net charge
If objects don’t like having a net charge, then how does it happen?

12. Silk on glass Þ glass ® (+) Who loses electrons? The glass
Fur on rubber Þ rubber ® (-)
The fur 12

13. When objects get Charged:
Must obey Law of Conservation of Charge
Charges may be transferred among different atoms, materials, or objects but all charge is accounted for.
NO NEW charges are created nor are any charges destroyed.
Only electrons can move

14. Remember: An excess of electrons results in: A negative charge
A shortage of electrons results in:
A positive charge
ONLY ELECTRONS MOVE

15. How Do Charges Behave in Materials?
Conductor:
Allows electrons to move easily
Metals, why?
Metals lose electrons, (not held tightly)
Insulator:
Does not allow electrons to move easily
Non metals. Glass, plastic, dry wood. Why?
Electrons held tightly

16. Semiconductors – charges only move freely when certain conditions are met (i.e., heat, sufficient voltage, etc.) ex germanium, selenium, and silicon.
Superconductors – charges move effortlessly and cannot be stopped once they are moving

17. Objects become charged by…
Electrons are rubbed off one insulator onto another insulator
Friction
Conduction
Induction
Grounding
With a credit card 

18. FRICTION: e- rubbed off one insulator to another

19. Objects become charged by…
Friction
Conduction
Charging by CONTACT with
a charged object
Induction
Grounding

20. Charging by Conduction
Requires Contact Electrons transferred.
Results in:
Object with the same charge as original charged object.
Some electrons leave rod and spread over sphere.

21. Objects become charged by…
Friction
Conduction
Charging an object WITHOUT touching a charged object
Induction
Grounding

22. Induction
no contact occurs between charged object and neutral object..
Involves temporary rearrangement of electrons on neutral object
Neutral Object becomes “polarized” but net charge remains the same
If neutral polarized object is grounded, charge will become “opposite” of the charged object and is no longer temporary 22

23. Charging by Induction
Neutral objects can be temporarily attracted to charged objects by a process called POLARIZATON.

24. A negatively charged balloon is brought near a
neutral conducting sphere as shown below. As it
approaches, charge within the sphere will
distribute itself in a very specific manner. Which one of the diagrams below properly depicts the
distribution of charge in the sphere?

25. What is grounding?
Involves Transfer of excess electrons to and from the ground

26. Charging by Induction AND Grounding
permanent charge
polarization
grounding
The rod does not touch the sphere.  It pushes electrons out of the back side of the sphere and down the wire to ground.  The ground wire is disconnected to prevent the return of the electrons from ground, then the rod is removed.
The charge on the object is opposite if grounded

27. ~ 1750
“bells”
It consisted of two metal bells, one electrically connected to the earth (grounded) and the other connected to a lightning rod. Hanging between the two bells was a metallic ball suspended by an insulating (dielectric) thread. The lightning rod allows an electric charge to build up on one bell, which then attracts the metallic ball. When the ball hits this charged bell it becomes charged to the same potential and is immediately repelled. Since the grounded bell is charged oppositely, this attracts the ball towards it. When the ball touches and rings the grounded bell, the charge is transferred and the process repeats.
Lightening Bells 27

28. How can I tell if something is charged?

29. Pith Ball Experiment
Pith Ball and a Charged Rod
Pith Ball Experiment

30. In the beginning, the negative rod repels the electrons in the neutral pith ball to the ight. This causes the left side of the pith ball to obtain a net positive charge. Since opposite charges attract, the pith ball is attracted to the rod. When they touch, electrons are transferred to the pith ball giving it a net negative charge. Since the rod remains negative even after the transfer, it repels the negatively charged pith ball.

31. Electroscope-detects the presence of charge
When the leaves are charged, what will happen?
When the leaves are not charged, what will happen?

32. An electroscope is a device that detects static charge.
Negatively charged
Positively charged
The metal leaves of the electroscope move apart if a charged object is brought near the knob. Benjamin Franklin used a similar device when he investigated charges.

33. To review…
Induction results in an OPPOSITE CHARGE
Conduction results in the SAME CHARGE

34. Grounding is allowing charges to move freely along a connection between a conductor and the ground.
The Earth (the ground) is a practically infinite reservoir of electric charge.
Here a positively charge rod attracts electrons from the ground into the electroscope
Here a negatively charge rod repels electrons into the ground from the sphere

35. Static Electricity in our lives
Why are there more problems with static during the dry winter months?
The net charge of a water molecule is neutral, however it is a polar molecule. It can attract a build up of excess electrons
Some Static Electricity is due to friction
Clothes stick to each other in the dryer
How to solve this problem?
Dryer sheets. How do they work?
Dryer sheets contain lots of polar molecules to absorb the excess electrons and keep clothes neutral

36. Applications of Electrostatic Charging
                               
Fine mist of negatively charged gold particles adhere to positively charged protein on fingerprint.
                                                     
Negatively charged paint adheres to positively charged metal.

39. How the Microfiber Works: Proper use of our microfiber cloths means that 99% of the bacteria are removed from surfaces. This is important in areas such as your bathroom and kitchen. The microfiber effectively removes dust, dirt, grease, chemical residues, and micro-organisms.  The dry cloth employs static electricity (created when the synthetic fibers rub together) to attract dust and pull it into the fibers. The wet cloth removes dirt and moisture by capillary action, breaking the surface tension of water and grease, wicking them up. You're left with a clean, microorganism-free surface! By following our care instructions, these cloths will stand up to the rigors of every day use and washing, in both home and commercial settings. Microfiber cloths are very easy to use:Simply fold them, and wipe smooth surfaces with a flat section of cloth in contact with the surface. This means that the palm of your hand covers as much of the cloth as possible. When the cloth gets dirty, refold the cloth so a clean section will be in contact with the surface you are cleaning. Continue until all surfaces of the cloth are filled. This technique works for both wet and dry cleaning. To use the cloths wet, simply wet them in warm water, squeeze out excess water, and fold the cloth to wipe.*** Remember to not use chemical cleaners or soaps with the microfiber - use only water! 
To clean the cloths:
If the cloths are only slightly dirty, they can be rinsed with some dish detergent in warm water. Rinse well, hang to dry, and they are ready to be used again! The microfiber can be used every day, washed many times, and still retain its effective cleaning properties.
Wash dirty cloth in the washing machine with detergent. We recommend the Norwex Laundry Detergent, because it is free from fillers. However, any detergent can be used, as long as it does not contain bleach, fabric softeners, or chemical additives. It is also important to wash the cloths with lint-free laundry (not sweaters or bath towels).
Hang the cloths to dry, or use the dryer. If the cloths are not working well, they may be holding chemical residues or bacteria. Wash in the hottest cycle in your machine, and dry at the hottest dryer setting. Alternatively, they can be boiled on the stove top for several minutes.
To clean the dry mop, use our Rubber Static Brush to release dust and dirt from the mop into the garbage or outdoors. The mops can be machine washed as above. 

41. Lightning Becomes very “negative.” Becomes very “positive.”
WHO DETERMINED POSITIVE AND NEGATIVE? 41

43. How lightning forms – YouTube
how lightning works – YouTube
The Birth of a Lightning Bolt - YouTube

44. Four fundamental forces in nature
Gravity
Weak nuclear
Electromagnetic (electricity and magnetism)
Strong nuclear

45. EM force is a billion times stronger than gravity, why don’t we notice it?

46. Electrical Forces Why don’t we notice them?
The attractive and repulsive forces between the charges in Earth and the charges in your body balance out!!!!

47. Electromagnetic force is significant at atomic level. Things you know:
Atom has positively charged nucleus surrounded by negatively charged electrons
All electrons are identical (same mass; same quantity of negative charge)
All protons are identical (same mass; same quantity of positive charge)
Nucleus composed of protons and neutrons. Neutrons are neutral
Neutral atoms have equal protons and electrons so zero net charge

48. It is physical property of matter.
What exactly is CHARGE?
It is physical property of matter.
It comes in two flavors: “plus” and “minus.”
What is the unit for charge?
Coulombs (C)

49. What is the smallest charge possible?
Millikan Oil Drop Experiment
In 1910, Millikan was able to measure the charge of an electron.
The smallest charge possible is:
x Coulombs (C).

50. Definition of Coulomb Abbreviation: C SI unit for charge
One coulomb is NOT equal to the charge of 1 electron!!!!
1C ~ the charge of 6.25 x 1018 electrons
It is the amount of charge to pass through a cross-section of wire in 1 second when 1 Ampere (A) of current is applied.
(We’ll cover the amp later.)
Likewise the + charge of protons is associated with 6.25 x 1018 protons

51. Charge, (Coulombs per particle) # of particles in a Coulomb
Elementary Particles
Particle
Charge, (Coulombs per particle)
# of particles in a Coulomb
electron
-1.6 x 10-19
6.25 x 1018
proton
+1.6 x 10-19 51

52. Ex 1
A strong lightning bolt transfers 35 C to Earth. How many electrons were transferred?
(35 C) (6.25 x 1018 electrons)
2.19 x 1020 electrons

53. Coulomb’s Law
Charles-Augustin de Coulomb used a torsion pendulum to establish his law.

54. Electric Force q  charge, C (coulombs)
d  distance between charges, m
F  electric force, N
k  electrostatic constant x 109 Nm2/C2

55. What happens to F as charge increases?
What happens to F as r increases?
Decreases by inverse square
Look at kc. Is this a large or small value?
large
How is q described for a proton?
positive
For an electron?
negative

56. The Product of q1and q2
If the product, q1q2 ,is negative then the force is attractive.
If the product, q1q2 ,is positive then the force is repulsive.

57. An attracting or repelling force?
Ex 2: Two negatively charged balloons are 0.70m apart. If the charge of each is 2.0 x 10-6C, What is the electric force between the two balloons?
q1 = q2 = 2.0 x 10-6 C
d = r = 0.70 m
F = 9.0 x 10 9 N m2/C2 (-2.0 x 10-6 C)2
(0.70m)2
F = N
An attracting or repelling force?

58. F = 4.0 x 10-3 N d = 0.015 m q2 = Fd2 k q2 = (4x10-3N)(0.015m)2
Ex.3: Two equally charged balloons repel each other with a force of 4.0 x 10-3 N. If they are m apart, what is the charge of the each balloon?
F = 4.0 x 10-3 N
d = m
q2 = Fd2 k
q2 = (4x10-3N)(0.015m)2
(9x109Nm2/C2)
q1 = q2 = 1.0 x 10-8C

59. Ex 4: How many Coulombs are in a µC? 1 x 10-6
Two charges are separated by 3.0 cm. Object A has a charge of +6.0 µC. Object B has a charge of -6.0 µC. What is the force on Object A? Is the force attractive or repelling?
-360N, attractive

60. Ex 5
Two electrons exert an electrical force of x 10-8 N on one another.
Is this an attractive or repelling force?
Repelling
Calculate the distance between them.
Rearrange formula to solve for d
Use known charge for an electron
1.5 x m

61. Two charges create a force on one another
Two charges create a force on one another. If the charge of one object is doubled, how does the resulting force change?
F will double
What if charge of one object is tripled?
F will triple

62. Two charges create a force on one another
Two charges create a force on one another. If the distance between the objects is increased by a factor of 2, the force changes by a factor of?
F will decrease by a factor of 4
What if distance between the objects is tripled?
F will decrease by a factor of 9

63. Review………. How many electrons in one Coulomb? 6.25 x 1018 electrons
What is the charge of one electron
-1.6 x Coulombs (C)
How many protons in one Coulomb?
6.25 x 1018 protons
What is the charge of one proton
+1.6 x Coulombs (C).

64. Review………. How many electrons in one Coulomb? 6.25 x 1018 electrons
Calculate the charge of one electron
-1.6 x Coulombs (C)
How many protons in one Coulomb?
6.25 x 1018 protons
Calculate the charge of one proton
+1.6 x Coulombs (C).

65. Force and Fields Contact forces What we mostly deal with
Objects touch each other directly
Ex. A tennis racket hits a tennis ball
F=ma

66. Forces can occur without contact!
Action at a distance
Can you think of anything that applies a force without touching?

67. Gravity demonstrates action at a distance
What happens if you get too far away from the mass exerting the force?
The effects are less

68. What else applies an action at a distance?
Magnets!

69. What else applies an action at a distance?

70. Attracting and repelling forces of charges

71. The space that surrounds these things is altered Examples:
Magnets
Sun
Planets
Electric charge

72. Action at a distance depends on a field of influence
An object within the field may be affected by it
Can be scalar or vector
Magnitude only
Ex. Heat
Can be vector
Magnitude and direction
Ex. Gravity (one direction only since only attracts)
Ex. Electric (more than one direction; attracts and repels

73. Fields are NOT Force, they exert the force
Ex. A person pushes a box.
The person is not the force, he exerts the force!

74. Electric field
A field that exerts force that surrounds an electric charge or group of charges
Magnitude and direction (vector)

75. Electric field
How would you detect and measure an electric field around a charge?
Place another one nearby and see what happens!
Since all charges produce fields, come up with a model

76. Electric field model
Source charge: charge producing the field. Usually designated with a capital Q
Test charge: a mathematical creation
Always positive
Symbol: q’
Doesn’t exist
Infinitely small, thus produces no field of its own

77. What is the source charge if
The test charge q moves towards it?
Negative (attracts)
The test charge q moves away from it?
Positive (repels)
How would I draw these?

78. Where do you think the field is strongest?

79. What if I had more than one source charge
What if I had more than one source charge? What would the field lines look like?

81. Think: Where is the electrical potential energy of a positive test charge (q+) higher, at the point A or B? Why?
Point A. Because of it’s location, it is not where it “wants” to be. It took work to get it there!

82. The electric field is strongest in regions where the lines are close together and weak when the lines are further apart.

83. These fields can be detected in lab…
Threads floating on oil bath become polarized and align themselves with the electric field.

84. 84

85. 85

86. 86

87. 1. Force (Push or Pull) of Source Charge on Test Charge
How do I measure the strength of the electrical field around a source charge (Q)?
What factors do you think the electrical field strength is dependent on?
1. Force (Push or Pull) of Source Charge on Test Charge
2. Distance Between Source Charge and Test Charge

88. First let’s consider effect of force

89. Electric Field Intensity (Strength)
E - Electric Field Strength or Intensity (N/C)
F - Force experienced by a test charge at that location (N)
q’ - magnitude of the test charge placed at that location (C).

90. Ex 6 E = F/q’ E = 2N/ 1 x 10-10C E = 2 x 1010 N/C
A test charge has a magnitude of 1 x 10-10C. It experiences a force of 2N in an electrical field. What is the Intensity of the field?
Variables:
F = 2N
q’ = 1 x 10-10C
E = F/q’
E = 2N/ 1 x 10-10C
E = 2 x 1010 N/C

91. Ex 7
A test charge of 6 x uC is placed 200 mm from a proton (this is the source charge). What is the electrical force between them? What is the Field strength at this point? What is the direction of the field?
Are my variables in
the correct units?
Variables:
q’ = 6 x 10-26µC
p+= 1.6 x 10-19C
d = 200 mm
Variables:
q’ = 6 x 10-32C
p+= 1.6 x 10-19C
d = 0.2m
Now we can solve. This is a 2 step problem.
Step 1: Solve for force using Coulombs Law
Step 2: Use the calculated force and solve for Field Intensity

92. Ex 7 cont
A test charge of 6 x µC is placed 200 mm from a proton (this is the source charge). What is the electrical force between them? What is the Field strength at this point? What is the direction of the field?
F = kqq d2
Variables:
q’ = 6 x 10-32C
p+= 1.6 x 10-19C
d = 0.2m
F = (9 x 109C)(6 x 10-32C)(1.6 x 10-19C)
0.2m2
F = 2.16 x 10-39N
E = F/q’
E = 2.16 x 10-39N / 6 x 10-32C
E = 3.6 x 10-8 N/C

93. Remember: The direction of the electric field at a point in space is
the same as the direction in which a positive charge would move if it were placed at that point. The electric field lines or lines of force indicate the direction. -Q +
Electric field line flow Out of positive charges and into Negative charges.

94. Units: N/C The electric field intensity E at a distance d from a
source charge Q can be found without knowing the test charge!:
Q is often written lower case, but I do not want you to confuse source charges with test charges
Units: N/C

95. = 2.7x104 N/C, towards q or to the left
EX 8: What is the electric field intensity at a distance of 2 m
from a source charge of -12 μC? Include direction.
d = 2 m
q = -12 μC
q = -12μC
To determine the direction of the field, ask
If the source charge is negative do the
field lines go out or in?
= 2.7x104 N/C, towards q or to the left

96. How do I determine the field strength if there are multiple charges?

97. When more than one charge contributes to the field, the resultant field is the vector sum of the contributions from
each charge.
Where k : 9x109Nm2/C2
Units: N/C
Note we will look at direction of the field to know whether fields add or subtract at a point.

98. Remember this? -Q +
Electric field line flow Out of positive charges and into Negative charges.

99. r2 r2 X = kq1 + kq2 = (9 x 109)(8 x 10-6) + (9 x 109)(12 x 10-6)
Ex 9: Two charges q1=-8 μC and q2=+12 μC are placed
120 mm apart in the air. What is the electric field at the midpoint between them? ET
q1 = -8 μC
q2 = +12 μC
r = m E1 E2 - q1 X + q2
The fields have the same direction so they add:
out of positive
into negative
= kq1 + kq2
r r2
= (9 x 109)(8 x 10-6) + (9 x 109)(12 x 10-6)
(0.06) (0.06)2
E= 2.0 x x 107 = 5.0 x 107 N/C
to the left

100. r2 r2 X = kq1 - kq2 = (9 x 109)(8 x 10-6) - (9 x 109)(12 x 10-6)
Ex.10: Two charges q1=+8 μC and q2=+12 μC are placed 120 mm apart in the air. What is the electric field at the midpoint between them? ET
The fields are in opposite
directions so they subtract
q1 = + 8 μC
q2 = +12 μC
r = m E2 E1 + q1 X + q2
= kq1 - kq2
r r2
= (9 x 109)(8 x 10-6) - (9 x 109)(12 x 10-6)
(0.06) (0.06)2
E= 2.0 x x 107 = -1.0 x 107 N/C
E = 1.0 x 107 N/C to the left