Electrostatics
Static Electricity
After you take your clothes out of
the dryer, they sometimes are
stuck together. They stick together
because of static electricity. Static
electricity is the electric charge
at rest on an object. When
something is static, it is not moving. The charges of static electricity do
not move away from the object that they are in. So, the object keeps its
charge. Your clothes are charged by friction as they rub against each
other inside a dryer. As the clothes tumble, negative charges are lost by
some clothes and build up on other clothes. When the dryer stops, the
transfer of charges also stops. And because clothing is an insulator, the
built-up electric charges stay on each piece of clothing. The result of this
buildup of charges is static cling.
Electric Discharge
Charges that build up as static electricity on an object eventually leave the
object. The loss of static electricity as charges move off an object is called
electric discharge. Sometimes, electric discharge happens slowly. For
example, clothes stuck together by static electricity will eventually separate
on their own. Over time, their electric charges move to water molecules in
the air. Sometimes, electric discharge happens quickly. It may happen with
a flash of light, a shock, or a crackling noise. For example, when you wear
rubber-soled shoes and walk on carpet, negative charges build up on your
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body. When you reach out for a metal doorknob, the negative charges on
your body can jump to the doorknob. The electric discharge happens
quickly, and you feel a small shock. One of the most dramatic examples of
electric discharge is lightning. How does lightning form through a buildup
of static electricity? The Figure below shows the answer.
Lightning Dangers
Lightning usually strikes the highest point in a charged area because that
point provides the shortest path for the charges to reach the ground.
Anything that sticks up or out in an area can provide a path for lightning.
Trees and people in open areas are at risk of being struck by lightning. For
this reason, it is particularly dangerous to be at the beach or on a golf
course during a lightning storm. Even standing under a tree during a storm
is dangerous. The charges from lightning striking a tree can jump to your
body. Objects can become charged by friction, conduction, and induction.
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Friction
Charging by friction happens when electrons are “wiped” from one
object onto another. If you use a cloth to rub a plastic ruler, electrons
move from the cloth to the ruler. The ruler gains electrons and becomes
negatively charged. At the same time, the cloth loses electrons and
becomes positively charged.
Conduction
Charging by conduction happens when electrons move from one object
to another by direct contact. Suppose you touch an uncharged piece of
metal with a positively charged glass rod. Electrons from the metal will
move to the glass rod. The metal loses electrons and becomes positively
charged.
The friction of a rubbing
balloon on your hair causes
electrons to move from your
hair to the balloon. Your hair
and the balloon become
oppositely charged and attract
each other.
When a negatively charged
plastic ruler touches an
uncharged metal rod, the
electrons in the ruler travel to
the rod. The rod becomes
negatively
charged by conduction.
Induction
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A negatively charged balloon
makes a small section of a
metal beam have a positive
charge through induction.
Electrons in the metal are
repelled by and move away
from the balloon.
Charging by induction happens when charges in an uncharged metal
object are rearranged without direct contact with a charged object.
Suppose you hold a metal object near a positively charged object. The
electrons in the metal are attracted to and move toward the positively
charged object. This movement causes (or induces) an area of negative
charge on the surface of the metal.
Static electricity
,
, electric charge
negative charges
insulator, conductor ,
Lightning
Electrons
, Charging
friction
Friction , conduction
induction
Worksheet
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electric discharge
1. For each pair of terms, explain how the meanings of the terms
differ.
a. static electricity and electric discharge.
______Static electricity is the electric charge at rest on an object.
The loss of static electricity as charges move off an object is called electric discharge.
b. electrical conductor and electrical insulator
___electric conductor is an object which conducts the electric charges.
____electric insulator is an object which does not conduct electric charges.__
2. Which of the following is an insulator?
a) copper
b) rubber
c) aluminum
d) Iron
3. An object becomes charged when the atoms in the object
gain or lose
a) protons.
b) neutrons.
c) electrons.
d) All of the above
4. Give two examples of static electricity.
Your clothes are charged by friction as they rub against each other inside a dryer.
Rubbing a balloon in a piece of wool or your hair makes builds up a static charges.
5. List two examples of electric discharge.
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 when you wear rubber-soled shoes and walk on carpet, negative charges build up on
your body. When you reach out for a metal doorknob, the negative charges on your
body can jump to the doorknob.
 lightning.
6. Compare the three methods of charging.
Methods of charging
Friction
Conduction
Induction
Point of comparison
Definition
Charging by friction
Charging by
Charging by induction
happens when
conduction happens
happens when
electrons are “wiped”
when electrons move
charges in an
from one object onto
from one object to
uncharged metal
another.
another by direct
object are rearranged
contact.
without direct contact
with a charged object.
When you hold a
When you touch an
If you use a cloth to
Example
uncharged piece of
rub a plastic ruler,
metal with a positively
electrons move from
charged glass rod.
the cloth to the ruler.
Electrons from the
The ruler gains
metal will move to the
electrons and
glass rod. The metal
becomes negatively
loses electrons and
charged. At the same
becomes positively
time, the cloth loses
charged.
electrons and
metal object near a
positively charged
object. The electrons
in the metal are
attracted to and move
toward the positively
charged object. This
movement causes (or
induces) an area of
negative charge on
the surface of the
becomes positively
metal.
charged.
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7. Do the balloons have the same charge or opposite charges?
Explain your answer.
____these balloons have the same charges.
Because they repel from each other.
8. How would the photograph look
if each balloon were given the
charge opposite to the charge it
has now? Explain your answer.
___
if the balloons have opposite charges , one
of them is positively charged and the other is
negatively charged they would attract.
9. The statements below are false. For each statement, replace the
underlined term to make a true statement.
1. Charges flow easily in an electrical insulator . (electrical conductor…)
2. Lightning is a form of static electricity .
Resources:
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(…electric discharge…)
 Holt Science and Technology.
Physical Science
ISBN -13: 978-0-030-46228-3
Chapter 17 – page 474
 Websites:
http://www.google.com.qa/imgres?q=hires+static+charges&hl=en&sa=X&qscrl=1&nord=1&rlz=1T4RNRN_enUS444US445
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http://www.google.com.qa/imgres?q=repulsion+and+attraction+between+balloon
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