1. Rub a balloon against
your hair…
What can you remember from G10?

2. Charge
Charge is a property of objects that causes them to be attracted to or repelled by other objects with charge.
Charge comes in two varieties
Negative
Positive
Protons carry positive charge
Electrons carry negative charge
Most macroscopic objects (table, book, banana, pencil) are uncharged as they have equal numbers of protons and electrons

3. Charged vs. Uncharged Structure of solids
Crystal lattice
Protons in nucleus; fixed and immovable
Electrons moveable in some materials
A positively charged object has lost electrons
A negatively charged objects has gained electrons

5. Charge is conserved A Fundamental conservation law
When one object rubs against another object, one object loses electrons, the other one gains the same number of electrons
Charge is never created or destroyed
Charge is always transferred in integer multiples of the elementary charge
Q=Ne

6. Charge (Q) is measured in coulombs (C) 1C ~ 6.25x1018 e
Smallest possible amount of charge:
1 extra electron: q = x C
1 missing electron: q = x C
= e = elementary charge …
For any charge q:
q = ne , where n = 1, 2, 3, etc…
Charge is quantized
Charge is conserved

7. The coulomb (selected for use with electric currents) is actually a very large unit for static electricity. It is common to use the metric prefixes.
1 mC = 1 x 10-6 C
1 nC = 1 x 10-9 C
1 pC = 1 x C

8. Charging by Contact (rubbing…) - - - - - - - - - - + + + + glass (rub)
silk
fur
plastic
(rub)
Charging by
Contact (rubbing…)

9. Separating Charge
A material on the bottom of the list will gain electrons from a material above it on the list…

10. Example
A piece of fur is rubbed on an acrylic rod. If the rod gains a net charge of -3 nC, how many electrons were transferred from the fur to the rod?

11. Example 2
A solid sphere has a net charge of –4 nC. How many electrons must be added or removed for the sphere to have a net charge of +5 nC?

12. Like charges repel each other. Unlike charges attract each other.
Electric Force RULE’s!
Like charges repel each other.
Unlike charges attract each other. + + - -
Force of repulsion - +
Force of attraction
Electric Force = Non-contact force

13. Opposites Charges Attract
Like Charges Repel

14. Use rubber gloves in the lab
Conductors (such as metals, tap or salt water, and the human body) are good at conducting away any extra charge.
Insulators (like plastic, rubber, pure water, and glass) will not conduct away extra charge.
Metal:
“free electrons”
Use rubber gloves in the lab
Touching it with your hand will discharge it

15. Some electrons leave rod and spread over sphere.
Charging by Contact  
Some electrons leave rod and spread over sphere.

16. Gold-leaf Electroscope Pith-ball Electroscope
Laboratory devices used to study the existence of two kinds of electric charge.
Gold-leaf Electroscope
Pith-ball Electroscope

17. The two negative charges repel each other.
1. Charge the rubber rod by rubbing against fur.
2. Transfer electrons from rod to each pith ball.
The two negative charges repel each other.

18. The two positive charges repel each other.
1. Charge the glass rod by rubbing against silk.
2. Touch balls with rod. Free electrons on the balls move to fill vacancies on the cloth, leaving each of the balls with a deficiency. (Positively charged.)
The two positive charges repel each other.

19. Opposite Charges Attract!
fur
Rubber
silk
glass
Attraction
Note that the negatively charged (green) ball is attracted to the positively charged (red) ball.
Opposite Charges Attract!

20. Charging by Induction    
Rod does not touch 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.

21. The law of conservation of electric charge: "The net amount of electric charge produced in any process is zero." Another way of saying this is that in any process electric charge cannot be created or destroyed, however, it can be transferred from one object to another.
Charged comb attracts neutral water molecules.
Charged comb attracts neutral bits of paper.

22. Explain in 2 sentences

23. - - - - - - Grounding Object is discharged or “grounded” +
The earth is a huge reservoir of positive and negative charge + -
© Laura Fellman

24. Earthing Petrol Tankers
Petrol rubbing against the pipe can build up a static charge which could cause an explosion
The tanker is joined to the ground with a wire to stop a charge building up