Static Electricity
What Is Static
Electricity?
• A stationary electrical
charge that is built up on
the surface of a material
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.
Where do charges come from?
Matter is made up of atoms.
+ Proton (positive charge)
–
neutron (neutral)
+
+
–
+
–
atom
– electron (negative charge)
nucleus
Where do charges come from?
If electrons = protons neutral
If electrons > protons  gaining electrons, negative
charge
If electrons < protons  losing electrons, positive
charge
Electro-negativity
+++++
++++
+++
++
+
Relative
electro-negativity
ranking for some
common materials
from electron donating
materials (+, glass) to -electron accepting
--materials (-, teflon)
--------
•
•
•
•
•
•
•
•
•
•
•
•
Glass
Human Hair
Nylon
Silk
Fur
Aluminum
Paper
Cotton
Copper
Rubber
PVC
Teflon
Where do charges come from?
Rubbing materials does NOT create
electric charges. It just transfers
electrons from one material to the other.
Where do charges come from?
When a balloon rubs a piece of wool...
+
–
–
–
–
–
–
wool
+
+
+
+
electrons are pulled from the
wool to the balloon.
The balloon has more electrons than
usual.
The balloon: – charged,
The wool: +charged
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.
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.
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...
- - - - - - induced
charges
attraction  top of the can: positive
buttom of the can: negative
++ +
+
metal
can
electrons of the can are pushed
away from the rod.
-
-
+
-
repulsion
& attraction > repulsion
Attraction of uncharged objects
Similarly, when charged rod is close to paper
scrap...
- - - - - - -
 attraction between the
attraction
rod and + charge >
repulsion between the rod
and - charge.
––– –
++ + +
––– –
++ + +
paper
molecules of paper align.
repulsion
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?
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.
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
C
Negative
B
Positive
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
C
Neutrons
B
Protons
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
near the rod and _____________
positive charge is induced on the side
away from the rod. The rod can attract the netural object
because _________
attraction between rod and – induced charge >
the ________
repulsion between rod and + induced charge.
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.
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.
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.
Why do gasoline tankers usually have metal
chains at the back?
When cars run, their tires and bodies are usually
friction For gasoline tankers, if the
charged by _______.
accumulated charge is large enough, _______can
be
sparks
explosion will occur if gasoline vapor is
produced and _________
ignited. Those metal chains conduct the charge on the
ground and avoid the danger.
bodies of tankers to the _______
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
•
Limit Exposure
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.
The End