1. The study of electrical charges at rest
Electrostatics
The study of electrical charges at rest

2. The word electricity comes from the Greek word elektron, which means “amber”
The Greeks observed that when the amber was polished with a piece of fur, it would attract small leaves and dust particles
We now know that this is caused by static electricity

3. Electrical Forces
Electrical forces arise from the interactions between electrically charged particles
Postive charges – protons (p+)
Negative charges – electrons (e-)
Opposite charges attract
Similar charges repel

4. Atoms
Atoms are made of a nucleus containing protons and neutrons (n0) surrounded by electrons
The atom as a whole usually contains the same number of protons, neutrons, and electrons.
If there are the same amount of positives than negatives…the atom is electrically neutral in charge.

5. Charging objects
If an electron is removed then it is no longer neutral
The atom now has one more positive charge than negative so it is positively charged.
Positively and negatively charged atoms are called ions.

6. Charging objects
When objects become charged, ONLY electrons are either gained or lost.
Why would electrons be the ONLY particle to be transferred?

7. Law of Conservation of Charge
Electrons are more easily stripped off of atoms than protons because they are found on the outside of the atom
Law of Conservation of Charge
No electrons are created or destroyed when objects become charged…only transferred
The net amount of electric charged produced in any process is zero
Balloons

8. When objects become charged, they tend to lose their charge over time.
Where does the charge go?
The charge usually leaks off into water molecules in the air
Water molecules polar, meaning their charge is not distributed evenly and have a positive and negative side (similar to a bar magnet)

9. Static Electricity The word ‘static’ means not moving
So static electricity is defined as charges that are not moving
It is easier to hold a static charge on a dry day rather than a humid day since the polar water molecule will steal the stored charge when colliding with the charged object

10. Insulators and Conductors
Insulators are materials that do not allow electric charge to move through it easily
Examples?
Conductors are materials that allow electric charge to move through it easily

11. When a piece of metal is placed across the two spheres, charge is allowed to move easily into the other object.
The positive particles want to repel each other and get as far away from each other as possible forcing their way throught the conductor.

12. The charges can not move through the air or through the wood to spread out, because they are not good conductors

13. What makes some materials good conductors is the way the electrons are bound very loosely to the atoms and can move freely within the material
In insulators the electrons are tightly bound to the atom

14. Charging by Contact
When two substances are in contact, one of them has to give up some of its loose electrons to the other
Usually charges are stripped away through friction caused when two objects are rubbed together

15. Charging by conduction
Any excess charges that are gained on a good conductor always resided on its outer surface regardless of shape.
Charges simply push each other away to the very extremities of the object
John Travoltage
If the object is not a good conductor, the object might have to be charged in various locations along the surface to spread the charge

16. Charging by Conduction

17. Charging by Induction
An object can become charged without contact, a charge can be ‘induced’.
Charging through induction occurs when another charged object is brought next to a neutral object and the charges separate

18. If the object is moved away the charges return to normal
If the object was grounded, the electrons would flow out of the object to leave a net positive charge on the object

19. Charge Polarization
When a charged object is brought near an insulator, there is no movement of free electrons
Instead, there is a rearrangement of charges within the individual atoms so that the atoms are electrically polarized (like the poles on a magnet)

20. Check your Understanding from The Physics Classroom Tutorial
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?

21. Check your Understanding
Two neutral conducting pop cans are touching each other. A positively charged balloon is brought near one of the cans as shown below. The cans are separated while the balloon is nearby, as shown. After the balloon is removed the cans are brought back together. When touching again, can X is ____.

22. Check your Understanding
A positively charged balloon is brought near a neutral conducting sphere as shown below. While the balloon is near, the sphere is touched (grounded).
At this point, there is a movement of electrons. Electrons move ____ .

23. Electroscope

24. Electric Field
The space around every electrically charged body creates an electric field.
Just as every object that has mass has a gravitational field around it
Electric field is a vector quantity
If a body with charge q experiences a force F at some point in space the Electric field E is

25. If a positive test charge was placed near the charges below, and vectors are pointing in the direction of the electric force on the test charge, what would be the charge of each? - +

26. Electric Field

27. Electric Force
The electric field acts similar to a field of gravity, so there will be a force acting on the charge
Coulomb’s law
q represents the charge of the particle measure in coulombs [C]
k is Boltzman’s constant equal to 9x109 N·m2/C2

28. Quantized charge
Charge in quantized so charge only exists in discrete amounts (1q, 2q, 3q…nq)
You can never lose a fraction of a charge
The charge of an electron is
e = x10-19 C
The charge on a proton is the same amount but (+)

29. Electric Potential
Just as mass has potential energy in a gravitational field, charge has potential energy in the presence of an electric field

30. A positive charge placed in this electric field will be pushed away buy the positive side and pulled towards it by the negative.
The potential will change to kinetic as it moves.

31. The opposite occurs if the charge is changed to a negative.
The negative charge will move in the opposite direction of the electric field

32. What is going to happen? Acts like a projectile on Earth - v

33. What is going to happen? - - - - - - - - - - - - - - - v + v +

34. Electric Potential Energy
The change in PE is equal to the work done to move a charge
W=Fd
And force is equal to Eq from
So we get the equation
W=qEd which is electric
potential energy

35. A difference in electric potential energy is called the potential difference
Potential difference is measured in volts
It measures the difference in PE between two points per unit of charge

36. Equipotential Lines
All points between charged objects that have the same potential
Hence Equal Potential
An equipotential line must be perpendicular to the electric field

37. Moving it requires no Work, the voltage doesn’t change.
If the point charge moves between the charges then work will be done and the potential energy will change
Moving it requires no Work, the voltage doesn’t change.
Charge has same potential energy along this line
16V
14V
12V
10V 8V