Static electricity is an electric charge that builds up on the surface of objects. It is caused by an imbalance of electrons between two objects, usually through friction. This can cause attraction between objects. Insulators cannot easily dissipate excess electric charge, allowing them to build up static electricity. Conductors readily distribute excess electrons and cannot build up a static charge as easily. Grounding an object provides a path for excess electric charge to flow to earth and neutralize the object.

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
+++++ • Glass
Relative • Human Hair
++++
electro-negativity +++
• Nylon
ranking for some • Silk
++
• Fur
common materials + • Aluminum
from electron donating • Paper
materials (+, glass) to - • Cotton
electron accepting -- • Copper
materials (-, teflon) --- • Rubber
---- • PVC
----- • 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
attraction ⇒ top of the can: positive
charges
++ + 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
attraction
++++ rod and + charge >
–––– repulsion between the rod
paper ++++ and - charge.
––––
repulsion

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,
negative charge
______________ is induced on the side of the object
positive charge
near the rod and _____________ is induced on the side
away from the rod. The rod can attract the netural object
attraction
because _________ between rod and – induced charge >
the ________ between rod and + induced charge.
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
friction
charged by _______. For gasoline tankers, if the
sparks
accumulated charge is large enough, _______can be
explosion
produced and _________ will occur if gasoline vapor is
ignited. Those metal chains conduct the charge on the
ground
bodies of tankers to the _______ and avoid the danger.

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

45. Limit Exposure

46. 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

47. The End