1. Static Electricity

2. What Is Static Electricity?
A stationary electrical charge that is built up on the surface of a material

3. Two kinds of charges
After being rubbed, a plastic ruler can attract paper scraps.
Ruler carries electric charge.
It exerts electric force on paper.
This charging method is called charging by friction.
The interaction between static electric charges is called electrostatics.

4. Where do charges come from?
Matter is made up of atoms. + –
Proton (positive charge) +
neutron (neutral)
electron (negative charge) –
atom
nucleus

5. Where do charges come from?
If electrons = protons neutral
If electrons > protons  gaining electrons, negative charge
If electrons < protons  losing electrons, positive charge

6. Electro-negativity + + + + + + + + + + + + electro-negativity + +
- -
- - -
Glass
Human Hair
Nylon
Silk
Fur
Aluminum
Paper
Cotton
Copper
Rubber
PVC
Teflon
Relative
electro-negativity
ranking for some
common materials
from electron donating
materials (+, glass) to
electron accepting
materials (-, teflon)

7. Where do charges come from?
Rubbing materials does NOT create electric charges. It just transfers electrons from one material to the other.

8. Where do charges come from?
When a balloon rubs a piece of wool...
electrons are pulled from the wool to the balloon. + – –
The balloon has more electrons than usual.
wool
The balloon: – charged,
The wool: +charged

9. Insulators and conductors
Insulators: materials that do NOT allow electrons to flow through them easily.
Insulators can be easily charged by friction as the extra electrons gained CANNOT easily escape.

10. 4 Insulators and conductors
Conductors: materials that allow electrons to flow through them easily.
Conductors CANNOT be easily charged by friction as the extra electrons gained can easily escape.

11. Induction: The production of a charge in an uncharged body by bringing a charged object close to it
When negatively charged rod is put near a metal can...
electrons of the can are pushed away from the rod. -
induced charges
 top of the can: positive
attraction +
buttom of the can: negative
& attraction > repulsion -
metal can
repulsion

12. Attraction of uncharged objects
Similarly, when charged rod is close to paper scrap...
molecules of paper align. -
 attraction between the rod and + charge > repulsion between the rod and - charge.
attraction + –
paper
repulsion

13. Electricity
Static

14. Static Discharge
Human body can not feel less than 2,000 volts of static discharge
Static charge built up by scuffing shoes on a carpet can exceed 20,000 volts?

16. Gas Station Fires
Carol said a static gas pump fire is blamed for burning her daughter so badly she needed skin grafts on her legs.
Carol had put the gas pump nozzle on automatic and re-entered her car to write a check. When her then-12-year-old daughter, wearing a sweater and jacket that may have created static electricity, reached for the nozzle, flames suddenly ignited her clothing.

17. A balloon has a negative charge when rubbed by a woollen cloth.
1 If the balloon can attract some paper scraps, which of the following cannot be the charge of paper scraps?
A Neutral B Positive
C Negative

18. A balloon has a negative charge when rubbed by woollen cloth.
2 During rubbing, what have been transferred between the woollen cloth and the balloon?
A Electrons B Protons
C Neutrons

19. How does a positively charged rod attract a neutral object?
When a + charged rod is put near neutral object, ______________ is induced on the side of the object near the rod and _____________ is induced on the side away from the rod. The rod can attract the netural object because _________ between rod and – induced charge > the ________ between rod and + induced charge.
negative charge
positive charge
attraction
repulsion

20. Grounding What is grounding?
An object is grounded when it is connected to the earth through a connecting wire.
If a charged conductor is grounded, it will become neutral.

21. Grounding b How does grounding occur?
When we touch a metal ball of positive charge... + +
electrons flow from the earth to the metal ball to neutralize the metal ball. + + + –
Metal ball becomes neutral.

22. Grounding How does grounding occur?
Similarly, if the metal ball is of negative charge... – –
extra electrons flow from the metal ball to the earth and the ball becomes neutral. – – – –

23. Why do gasoline tankers usually have metal chains at the back?
When cars run, their tires and bodies are usually charged by _______. For gasoline tankers, if the accumulated charge is large enough, _______can be produced and _________ will occur if gasoline vapor is ignited. Those metal chains conduct the charge on the bodies of tankers to the _______ and avoid the danger.
friction
sparks
explosion
ground

24. Lightning kills more than 60 people and
injures more than 400 people a year in the US
one mile every five seconds
about 20,000 C
Voltage of up to 1.2x108 volts

46. Limit Exposure

47. Do Now
Write a paragraph about the cartoon. Tell what he is trying to do. Will it work and why? What do you think will happen? Use the following words, static electricity, lightning, electrons, positive and negative charges.

48. The End