kuliah 1 fmax0114 sesi201314 elektrostatik
TRANSCRIPT
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FMAX0114 : ELECTROSTATIC
Pn Hashlina Rusdi
Room: 217
GENERAL CONTENT
Charges
Electric charges: Coulombs LawElectric field: flux and Gausss Law
Electrical potential: Charge distribution and electric
potential energy
Capacitors:
Dielectric and energy storage
Combination of capacitors [series & parallel]
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REFERENCES
1. College Physics sixth edition
Thomson publications {penulis:serway/Faughn}
2. College Matriculation Physics Semester I&II
IPTA Publications. {Penulis: pensyarah PASUM}
3. College Matriculation Physics 3000 best Problem-
Solving Strategies semester I&II
SAP publications. {Penulis; Pensyarah PASUM}
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16. Electric Charge,
Electric Forces andElectric Field
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16.1: Properties of Electric
Charges Two types of charges exist
They are called positive and negative
Like charges repel and unlike charges attract
one another Natures basic carrier of positive charge is the
proton
Protons do not move from one material to anotherbecause they are held firmly in the nucleus
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16.1: Properties of Charge
Charge is quantized
All charge is a multiple of a fundamental unit
of charge. symbol: e
Electrons have a charge ofe
Protons have a charge of +e
The SI unit of charge is the Coulomb (C)
e = 1.6 x 10-19 C
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16.1: Properties of Charge
Natures basic carrier of negative charge isthe electron
Gaining or losing electrons is how an object
becomes charged Electric charge is always conserved
Charge is not created, only exchanged
Objects become charged because negativecharge is transferred from one object toanother
The arithmetic sum of the total charge
cannot change in any interaction.
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Objects can be charged by rubbing
Rubbing charges objects by moving electrons
from one to the other.
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Charge comes
in two types,
positive and
negative; likecharges repel
and opposite
charges attract
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16.2 Electric Charge in the Atom
Atom:Nucleus (small,
massive, positive
charge)
Electron cloud (large,
very low density,
negative charge)
Atom is electrically
neutral.
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16.2 Electric Charge in the Atom
Polar molecule: neutral overall, but charge notevenly distributed
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16.3 Insulators and Conductors
Conductor(metals):Charge flows freely
Insulator (Most other
materials):
Almost no charge flows
Some materials are semiconductors. (Si , Ge)
The characteristics of semiconductors are
between those of insulators and conductors
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Conductors
Conductors are materials in which the
electric charges move freely
Copper, aluminum and silver are good
conductors
When a conductor is charged in a small
region, the charge readily distributes itself
over the entire surface of the material
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Insulators
Insulators are materials in which electric
charges do not move freely
Glass and rubber are examples of insulators
When insulators are charged by rubbing, only
the rubbed area becomes charged
There is no tendency for the charge to move into
other regions of the material
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Charging by Conduction
A charged object (the rod) is
placed in contact with
another object (the sphere)
Some electrons on the rodcan move to the sphere
When the rod is removed,
the sphere is left with a
charge
The object being charged isalways left with a charge
having the same sign as the
object doing the charging
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Charging by Induction
When an object is connected
to a conducting wire or pipe
buried in the earth, it is said
to be grounded
A negatively charged rubber
rod is brought near anuncharged sphere
The charges in the sphere
are redistributed
Some of the electrons inthe sphere are repelled
from the electrons in the
rod
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Charging by Induction, cont
The region of the sphere nearest thenegatively charged rod has an excess ofpositive charge because of the migration
of electrons away from this location A grounded conducting wire is connected
to the sphere
Allows some of the electrons to move from thesphere to the ground
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Charging by Induction, final
The wire to ground is removed, thesphere is left with an excess of induced
positive charge The positive charge on the sphere is
evenly distributed due to the repulsionbetween the positive charges
Charging by induction requires nocontact with the object inducing thecharge
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16.4 Induced Charge; the Electroscope
Metal objects can be charged by conduction:
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16.4 Induced Charge; the Electroscope
They can also be charged by induction:
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16.4 Induced Charge; the Electroscope
Nonconductors wont become charged byconduction or induction, but will experience
charge separation:
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16.4 Induced Charge; the Electroscope
The electroscope can be charged either by
conduction or by induction.
The electroscope can be used for detecting
charge:
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16.4 Induced Charge; the Electroscope
The charged electroscope can then be used to
determine the sign of an unknown charge.
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16.5 Coulombs Law
State that the electric force between two point
charges is proportional to the product of thecharges and inversely proportional to the distance
between them.
This equation gives the magnitudeof the force.
The value of k;
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16.5 Coulombs Law
The proportionality constant k can also bewritten in terms of , the permittivity of free
space:
Charge on the electron:
Electric charge is quantized in units of the
electron charge.
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16.5 Coulombs Law
The force is along the line connecting the
charges, and is attractive if the charges areopposite, and repulsive if they are the same.
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A 4.5 109 C charge is located 3.2 mfrom a2.8 109 C charge. Find the
electrostatic force exerted by one
charge on the other.
Example 1:
E l 1
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9 92
1 2 9
22 2
4.5 10 C 2.8 10 CN m8.99 10
C 3.2 m
ek q q
Fr
81.1 10 N
Since the charges have opposite signs, the
force is one of attraction .
Its magnitude is
A 4.5 109 C charge is located 3.2 m from
a2.8 109 C charge. Find the electrostatic
force exerted by one charge on the other.
Example 1:
Solution 1: