1. Electricity

2. What is electricity?
--- All the phenomena caused by positive and negative charges ---

3. Electric Charges
The electric charge is a property of protons and electrons. A proton is positively charged, and an electron is negatively charged.

4. Electric Charges
A negatively charged object has a surplus of electrons (more electrons than protons)

5. Electric Charges
A positively charged object has a deficit of electrons (fewer electrons than protons)

6. Electrical charges Proton  + charge Electron  - charge
A negatively charged body contains more electrons than protons.
A positively charged body contains fewer electrons than protons.

7. Electric Charges
elementary charge- charge carried by an electron or a proton. It is x 1019 C.
Coulomb- unit of measure of the electric charge. A Coulomb is equivalent to the charge of 6.25 x 1018 electrons or protons.

8. Example
After charging a piece of fabric, Jonathan calculates that it has lost 2x1015 electrons.
a) What is its charge in coulombs?
2x1015 electrons/ 6.25x1018
= C
b) Is this charge positive or negative?

9. Forces of Attraction and Repulsion
Similar electric charges (two positive charges or two negative charges) repel each other
Opposite electric charges (one positive and one negative charge) attract each other

10. Forces of Attraction and Repulsion
electric force- force that permits the attraction or repulsion between charges
law of conservation of charge- electric charges can not be created nor destroyed; they can only be transferred from one object to another

11. Most objects are electrically neutral [equal numbers of positive and negative charges (protons and electrons)]
We can however give a charge to an object by transferring electrons from one place to another (electrification).

12. Electroscope

13. Conductors and Insulators
a substance that permits charges to circulate freely
Ex: metals, electrolytic solutions
Insulators
a substance that does not permit charges to circulate freely
Ex: wood, plastic, glass, paper, ceramic, rubber, silk, air

14. Semi-conductors conductibility depends on different factors
Often used in electronics
Ex: carbon, metalloids

15. Static Electricity
phenomena linked to charges at rest

16. Charging by Rubbing
When two objects are rubbed together, certain atoms from one take the valence electrons of the other. This results in two charged objects with opposite signs.

17. Charging by Rubbing Affinity Substance
High affinity to receive electrons (tendency to become negatively charged)
High affinity to donate electrons (tendency to become positively charged)
Plastic
Gold
Nickel, copper
Rubber
Sulfur
Wood, yellow amber, resin
Cotton
Paper
Silk
Lead
Wool
Glass

18. Charging by Conduction
charge an object by placing it in contact with another object that is already charged. The charges are shared between the two objects. The result is two charged objects with the same sign but the charge is weaker than in the original object.

19. Charging By Induction action that occurs without direct contact
charged object comes close to a neutral object, without touching it
charges with opposite signs progressively accumulate on the side close to the charged object. At the same time, if the second object is a conductor, an equal number of opposite charges accumulates on the other side of the object, conforming to the law of conservation of charge.

20. Charging By Induction

22. In class work
p.172 # 1,2,3,7,8