Static Electricity
Remember that most atoms are made up of
three subatomic particles:
1.
Protons
2.
Electrons
3.
Neutrons
These are arranged in the following manner:
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Because the electrons are outside the
nucleus, they are much more likely to be
transferred from one object to another.
When two substances are rubbed together,
electrons are transferred from one to
another.
The one which gains electrons becomes
negatively charged and the one which loses
electrons becomes positively charged. Both
of these objects will attract neutral ones.
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Law of Electric Charges
The Law of Electric Charges states that:
Ø Like charges repel
Ø Opposite charges attract
The Law of Electric Charges states that:
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Quick Review
Remember that most atoms are made up of three subatomic
particles:
1.
2.
3.
According to the Bohr -Rutherford model, they are arranged in the
following manner:
Because the ________________ are outside of the nucleus, they
are more likely to be transferred from location to location. This
may be done in one of three ways.
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Transfer of Electric Charges
There are three ways in which electric
charge can be transferred:
1.Charging by friction: As two objects
rub together, electrons move from one
object to another. The electrostatic
series can be used to determine which of
the objects will gain electrons and which
will lose them.
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2.Charging by contact: Electric charge
can sometimes be transferred by simply
touching one object with another.
3.Charging by induction: Transfer of
charges due to a charged object being
close to an uncharged object.
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Charging By Friction
Static electricity can be caused by rubbing two
different substances together. This is charging
by friction. Before being rubbed, both objects
are neutral which means they have the same
number of protons and electrons. When they
are rubbed, one object will lose electrons and
become positively charged. The other object
will gain electrons and become negatively
charged. Remember the protons and neutrons
never move.
To determine which object in the pair will
become positively charged and which will be
negatively charged, we use the Electrostatic
Series.
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The Electrostatic Series
This is a chart which list objects in the order
that they are able to hold onto their electrons
(or gain others). The object that is closer to the
top of the chart is always the positive one. It
has a loose hold on its electrons so will lose
them. The object that is closer to the bottom is
the negative one. It has a strong hold on its
electrons and will likely gain other electrons.
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The Electrostatic Series
Acetate
Glass
Wool
Cat’s fur, human hair
Calcium, magnesium, lead
Silk
Aluminum, zinc
Cotton
Paraffin wax
Ebonite
Polyethylene (plastic)
Carbon, copper, nickel
Rubber
Sulphur
Platinum, gold
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Use your electrostatic series to determine which object in each pair
will become positively charged and which will become negatively
charged:
Object Pairs
wool and acetate
silk and wool
ebonite and glass
rubber and cotton
fur and silk
hair and rubber
balloon
Positively charged
Negatively charged
In each case, indicate which pair will result in attraction and which
will result in repulsion:
1. + and + ______________________
2. + and - _______________________
3. – and - _______________________
4. Acetate and silk after being rubbed together
__________________
5. Silk (that has just been rubbed with wool socks) and a
negatively charged rubber balloon. _________________
When two substances are rubbed together, electrons are transferred from one substance to
the other.
The one which gains extra electrons becomes ______________ charged. The one which loses
electrons becomes _______________ charged.
To figure out which object will gain electrons and which will lose them, we use the
______________________________.
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Charging By Contact
Uncharged (neutral) objects can become
charged if they come into contact with charged
objects. When an uncharged object is charged
with a neutral one, it will take on the same
charge as the one that touches it.
If a negatively charged ebonite rod touches a
neutral pith ball, the pith ball will also become
negatively charged. The two objects will now
have the same charge and will repel each other.
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Charging By Contact
We have learned that electrons can be transferred by the
process of friction. Another way to transfer electric charge
is by _______________________. This simply means
touching a ____________________ one with a charged
one. The charged object might be positive or negative, it
doesn’t matter.
When charging by contact, the neutral object takes on the
__________________ charge as the object which touched
it.
Example: Touch a neutral pith ball with a negatively
charged ebonite rod. What charge will the pith ball have
after being touched? _____________________________
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Charging by Induction
The third and final way to transfer electric
charge is by induction. This requires
moving a charged object near, but not
touching, a neutral one.
Assume that a balloon has been charged by
rubbing it against your hair (friction) and is
now negatively charged. The nearby wall is
neutral meaning it contains an equal
number of positive and negative charges.
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As the negative balloon approaches the
neutral wall, it will repel the negative
charges at the wall’s surface, leaving behind
the positive charges. The surface of the
wall is now said to be positive and since
opposites attract, the balloon sticks to the
wall.
This type of induction is referred to as
temporary induction as soon the charges in
the wall will move back to their original
position and the balloon will fall off the
wall.
When charging by induction, the once
neutral object always takes on the opposite
charge to the object which approached it.
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Grounding
One way to protect ourselves against
electric shock is grounding. This means
directing the electricity into the ground
with a conductor. Some people who work
around a lot of electric charge wear
grounding straps.
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Insulators and Conductors
Conductors are materials that allow
electrons to move freely through them.
Metals are good conductors. One popular
conductor is copper wire.
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Insulators are materials that do not allow
electrons to move freely through them.
Static charge remains in place in an
insulator. Sometimes insulators can be
used to protect us from electric shocks. For
example, electric cords are often covered
with plastic to protect us.
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Review Insulators and Conductors
Answer the following on a separate piece of paper.
1. Define insulator and give two examples.
2. Define conductor and give two examples.
3. Why do our metal water taps not give us an electric charge?
4. What is the method of charging which requires rubbing one object with another?
5. What is the method of charging an object which simply requires touching it?
6. Give two examples, from your everyday life of charging by contact.
7. What charge does an object receive if it is charged by contact?
8. Define neutralization.
9. What is another term for neutralization?
10. What does it mean if an object is grounded?
11. Why does the earth itself not give us an electric charge?
12. Which types of objects tend to hold their electric charge very well?
13. Which types of objects tend to lose their electric charge more quickly?
14. Does a positively charged object only attract a negatively charged one? Explain.
15. How does a lightning rod work?
16. Ques. 1-4 on page 489 (SNC1D1).
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Lightning
Lightning is a natural process where electric
charges are moving through the air. We see
lightning as a jagged path caused by the
electric charges trying to find the fastest
path to the ground. The charges are drawn
to tall buildings because these shorten their
path to the ground.
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Lightning Rods
A lightning rod may be placed on the top of
a building. It is usually made of metal (a
conductor) and is long and pointed so it will
be the tallest part of the building.
The lightning rod should be the part of the
building first hit by the lightning and then
should channel the lightning into the
ground. Lightning always seeks the fastest
route to the ground.
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Static Electricity Review
1. Define static electricity.
2. Explain how you can give an electrostatic charge to a neutral object
by contact.
3. When you bring a charged object near to, but not touching, a neutral
one, what would you expect?
4. What does rubbing (friction) do to the two objects involved?
5. Can the protons in an atom move?
6. If a material gains electrons, what charge will it have?
7. What is conductor? Give an example.
8. List two common insulators.
9. Is dry air a conductor or an insulator?
10.What is grounding?
11.How does a lightning rod work?
12.What is static cling? Why does it occur more in the winter time?
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