1. Static Electricity Physics Mr. I

2. Part I History Charge and its Conservation
Conductors, Semiconductors, Insulators
Methods of Charging

3. History Electron means “amber” in Greek
Thales of Miletos 600 BC discovered properties by Greek.
He rubbed amber (mineral) with cat fur and attracted feathers.

4. Ben Franklin’s Kite Experiment (1740’s)

5. Leyden Jar

6. Benjamin Franklin
1740’s lightning experiment with kite, key and Leyden jar (stores static electricity).
Franklin developed the lightning rod.
Proposed conservation of charge.
Saw electricity as a flowing fluid and called the flow direction positive.

7. Law of Conservation of Electrical Charge
The net charge of an isolated system remains constant.

8. Example:
An object of +10C touched an identical object that was neutral. What is the charge of each object?

9. Law of Charges
Like charges repel
Opposite charges attract

10. J(oseph) J(ohn) Thomson (1897, England)
He discovered the electron.
He found that the mass of the electron is about 1/1800 of the mass of a hydrogen atom.
He won the Nobel Prize (1906) for his discovery of the electron.

11. JJ Thomson with the CRT

12. Cathode Ray Tube

13. Cathode Ray

14. Electrical Charge
Symbol: q
Unit : Coulomb, C

15. Charge and Mass of the Electron
Charge of Electron:
1.6 x C (Coulombs)
Mass of Electron:
9.11 x kg.

17. Positively charged objects lost electrons.
Example: Rubbing a glass rod with silk.
Rod becomes + (loses electrons)
Silk becomes - (gains electrons). 

18. Negatively charged objects have gained electrons.
Example: rubbing a rubber rod with fur.
Rubber Rod: - charged
Fur: + charged

19. Note
Negatively charged objects have more mass than an identical neutral object, since each extra electron has a mass of 9.11 x kg.

20. Types of Materials in terms of Electrical Conductivity
Conductors (metals)
Semiconductors (germanium, silicon)
Insulators (wood, glass, rubber)

21. Electrostatic Charging Methods
Friction
Conduction
Induction

22. Charging by Friction
The two objects wind up with opposite charges.

23. Triboelectric Series - Celluloid
+ Fur (rabbit) Glass Wool Fur (cat) Lead Silk Human skin, Aluminum Cotton Wood Amber Nickel, Copper, Brass, Gold Rubber Sulfur
- Celluloid

24. Charging by Conduction (direct contact)
The objects end up with the same type charge.
If the charges are equal in size, they share the charge equally.

25. Charging by Induction Objects ends up with opposite charge.
Involves grounding.

26. Electroscopes are used to test the charge of an object.

27. When a charged object is brought near the electroscope, its leaves spread apart.

28. When a charged object touches an electroscope, the electroscope is now charged.

29. What was the charge of the object that touched this electroscope?

30. Polarization

31. Part II
Coulomb’s Law

32. Coulomb’s Law
1785,Charles Augustin Coulomb (French scientist)
F = k q1q2
______ d2
k = 9 x 109 Nm2/C2
d (or r): distance between the charges.
q : charge of each object.

33. The Direction of the Electrical Force

34. Coulomb’s Law is an Inverse Square Law

35. The electrical force is one of the four fundamental forces.

36. Comparison with Gravitational Force
What are 3 differences between the electrical force and the gravitational force?

37. Comparison with Gravitational Force
What are 3 differences between the electrical force and the gravitational force?

38. Example 1
A charge of 2mC is 0.5 m from a charge of 3mC. Find the electric force.

39. Example 2
Three charges are positioned as shown. Find the force acting on the 2 C charge.

40. Example 2
Three charges are positioned as shown. Find the force acting on the 2 C charge.

41. Example 3
Two equal charges are located 1m from each other. The force acting between them is 2N.
How many Coulombs is each charge?
Answer: 15μC