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8/12/2019 Kuliah 1 FMAX0114 Sesi201314 Elektrostatik

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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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They can also be charged by induction:


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Nonconductors wont become charged byconduction or induction, but will experience

charge separation:


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The electroscope can be charged either by

conduction or by induction.

The electroscope can be used for detecting

charge:


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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:

kuliah 1 fmax0114 sesi201314 elektrostatik

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