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Natural Science

FES 150

Lecturer:Mr. Ayman Abulail

Electric Charge and Electric Currents

Prepared by:

Ahmed Mohammed Al Sayari 200910383

Hassan Abaas Al Bloushi 2009



Table of Contents

Table of Contents ........................................................2

Abstract .......................................................................2

Introduction .................................................................3

Charles-Augustin de Coulomb was born on 14 June

1736 in Angoulême, France. His father Henri

Coulomb, was an inspector of the Royal Fields in Montpellier. His mother, Catherine Bajet, came from

a wealthy family in the wool trade. He is best known

for developing Coulomb's law and The SI unit of

charge, the coulomb, was named after him. He did

on 23 August 1806...................................................9

Conclusion .................................................................15

Abstract

What is electricity? Where does is come from? Who

discovered it? What is it? These are some questions

that people usually don’t think about these days. Youturn on a switch and the light comes on; you put your

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keys in the ignition and turn the car turn on. These

things are some of the things we should think of and

understand what is happening behind that switch or in

the battery of the car or mobile phones, computer andall electric devices. We hear about positive and

negative charge but do not understand them and how

we use them and where they come from. Sometimes

you feel a shock when touching a door knob or while

shaking another person’s hand. What is that shock you

felt and why and how is it happening. We use the units

of Ohm and coulombs but where did these come from

and what do they represent in the world of physicsand electronics. We have many materials with

different properties. Each material has something

special that makes it different from other materials. In

electricity there are special materials that are used in

wires and other electrical devices. Why we use these

material and not other materials is a question in

addition to the pervious questions that need to beanswered.

Introduction

Electric charge and electric currents are very

important to our lives today. In the case of electric

charge we will discuss the different charges and howthey are formed. In addition to static electricity which

talks about the repletion and attraction factor of

charges and signs. Coulombs law and the discovery of

this formula that discusses the forces exerted on an

electric charge and the magnitude of these forces.

These are very important because without these we

would have faced many problems and couldn’tdevelopment and enhance our technology.

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Furthermore electric current has a major role in or

lives. We find current in all of your wires and electrical

devices. Some of the factors in electric current are the

electric battery and how it works, Ohm’s law and therelation of the voltage and resistance to the current. In

addition to resistivity and the different materials used

for electric current. These are other factors are some

greatest discoveries in the world which opened new

doors of technology and inventions. The topic is

interesting because it talks about things that all

people use everyday but don’t really understand the

physics behind it. These discoveries and factors havebeen discovered many years before and since that

time people were trying to develop and enhance these

factors to become more efficient and reliable. Some of

these factors are still being used as it was first

discovered and formulated many years ago such as

Ohm’s law and Coulombs law.

Electric Charge

Static Electricity: Electric Charge and its Conversation

Static electricity is one of the major discovers that

people found out about by coincidence. It was first

known as the “amber effect”, in which the ancient

knew that by rubbing a piece of amber tree with a

cloth, makes the amber attract small pieces of leaves.

We can also feel this even now in our daily lives such

as the attraction we feel when getting out clothes

from the dryer. Even sometimes we feel a shock when

touching a metal door knob. These are all caused as aresult of rubbing in which objects get charged and is

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then said to be a net electric charge. After some

experiments we found out that their where different

charges. One of these experiments is the plastic and

glass experiment. They rub both of these objects will asilk to charge them. Then we try charging another

glass in the same way and bring it close to the first

glass they repelled each other. But when the glass is

brought next to the plastic they attracted. This

experiment is illustrated below:

They found that there are only two kinds of electric

charges and came up with a law that states that:

unlike charges attract and like charges repel.

The charges were referred to as negative and

positive by philosopher and scientist Benjamin

Franklin. He said “that when ever a certain amount of

charge is produced on one object, an equal amount of

the opposite type of charge is produced on another

object.” “For example, when a plastic ruler is rubbed

with a paper towel, the plastic acquires a negative

charge and the towel acquires an equal amount of

positive charge. The charges are separated, but the

sum of the two is zero.” By this example we

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established what we know today as the law of

conservation of electric charge which states that the

net amount of electric charge produced in any process

is zero.

Insulators and Conductors

After many experiments we found out that there

are some materials that let electricity or electric

charges to flow and some do not allow. One of these

experiments are having two object in which one of them is charge and the another is neural (having no

charge) and having some kind of metal touching both

objects, the neural object will be charged with the

same charge as the first object. In the same conditions

instead of using a metal object to touch both objects

we use a wooden object the result will be neural and

nothing will happen to either objects. After manyexperiments we found out that materials that contain

iron are conductors (allow electric flow) and materials

such as wood and rubber are insulators (do not allow

electric flow). There are also some materials that are

not really good conductors nor are good insulators and

are not considered neither insulators nor conductors

such as silicon and germanium, these materials are

known as semiconductors.

Induced charge

An object having as positive charge is brought

close to a neutral object. When both of them touch the

neural will acquire a positive charge, meaning that the

free electrons moved from one object to the other.

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This type of charging is called charging by conduction.

Another kind of charging objects is induced charge, for

example let us take the example before with the two

rods one with a positive charge and the other with aneutral charge. If we put the positive charged rod on

one end of the neural rod without touching, the free

electrons will not be able to leave the rod, but still be

able to move within the rod. Meaning it will form a

positive charge on the opposite side of the rod which

is far from the originally positive rod which is brought

close.

An electroscope is a deviceused to detect charge. In theelectroscope there is inside twomovable metal leaves. Theseleaves are connected to a metal

knob from the outside. Theapparatus works in two ways byusing conduction and inductioncharging methods. If a positivecharge is brought close to the knobwe will be using induction chargewhich will form a positive chargeon both leaves making them repeleach other. In the other case of conduction if a positive charge

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object touches the knob the whole apparatus acquiresthe net charge, making the leaves repel. The strongerthe charge the further apart they move.

By using the electroscopewe can only know if there is a

charge in the object but still we

do not know what charge is it a

negative or a positive charge,

as illustrated before if we use a

negative charge instead of a

positive we will still get the

same result. But we can figure

out the charge using the electroscope by using this

technique. First by using conduction there was a

negative charge in the apparatus, we bring a negative

object to the knob making the charges repel and move

apart even more, then bring another object which we

know is positively charged and touch the knob if the

leaves move a but closer than before then the originalsign was negative, this technique works either way for

positive or negative charges.

Coulombs Law

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Charles-Augustin de Coulomb was

born on 14 June 1736 in

Angoulême, France. His father

Henri Coulomb, was aninspector of the Royal Fields in

Montpellier. His mother,

Catherine Bajet, came from a

wealthy family in the wool

trade. He is best known for developing Coulomb's

law and The SI unit of charge, the coulomb, was

named after him. He did on 23 August 1806.

He studied the electric charge forces of attraction and

repulsion on other electric charges and wanted to

know the factors that affected the magnitude of these

forces. Then after many studies and experiments he

came up with this statement “the force one small

charged object exerts on a second one is proportional

to the product of the magnitude of the charge on one,

Q1 times the magnitude of the charge on the other,

Q2, and inversely proportional to the square of the

distance r between them”. This is illustrated in the

equation below:

This equation as mentioned before gives the

magnitude of the electric force that either object

exerts on the other. Furthermore the direction of the

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http://en.wikipedia.org/wiki/Angoul%C3%AAme

http://en.wikipedia.org/wiki/France

http://en.wikipedia.org/w/index.php?title=Royal_Fields&action=edit&redlink=1

http://en.wikipedia.org/wiki/Montpellier

http://en.wikipedia.org/w/index.php?title=Catherine_Bajet&action=edit&redlink=1

http://en.wikipedia.org/wiki/Coulomb's_law


http://en.wikipedia.org/wiki/SI_unit

http://en.wikipedia.org/wiki/Coulomb

http://en.wikipedia.org/wiki/France

http://en.wikipedia.org/w/index.php?title=Royal_Fields&action=edit&redlink=1

http://en.wikipedia.org/wiki/Montpellier

http://en.wikipedia.org/w/index.php?title=Catherine_Bajet&action=edit&redlink=1



http://en.wikipedia.org/wiki/SI_unit

http://en.wikipedia.org/wiki/Coulomb

http://en.wikipedia.org/wiki/Angoul%C3%AAme



electric force is always along the line joining the two

objects.

Electric Currents

Electric Battery

The people who discovered the electric battery were

Luigi galvanic and Volta. A battery

produces its energy by converting or

transforming chemical energy into

electrical energy this is the basic

phenomena of how it works. Today

we have many kinds of batteries and

electric cells. The basic battery

contains two rods made out of

dissimilar metals called electrodes. These electrodes are put in a

solution such as a dilute acid called

an

electrolyte. Such devices are called an electric cell and

having several cells together is considered to be a

battery.

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As shown in the figure we have two electrodes, one

made of Zinc and the other from Copper. They are

both put in sulfuric acid as the electrolyte. Theremaining part that is not in the solution is known as

the terminal where connections and wires are

connected. In this case the zinc electrode will start to

dissolve and then acquires a negative charge and the

copper gets a positive charge. If the electrodes are not

connected there will not be much flow in the cell which

will cause it to die.

Electric Current

For a battery to do its main

function and we need a

continuous path which connects

between the terminals of thebattery. This path then is

known as an electric circuit. We

use this in a light bulb, heater,

radio and many other things. In this case were we

have a continuous circuit from one terminal of the

battery to the other, the flow of charge in the wires is

called an electric current.

The current (I) is known as the amount of the charge

that passes through the conductor at any location

during the time interval as shown below:

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Electric current is measured in coulombs per second

known as Ampere, after the French physicist Andre

Ampere.

Ohm’s Law: Resistance and Resistors

This law was established by George Simon Ohm in

which he ran experiments to show that current in a

wire is proportional to the potential difference. To

have an electric current, a difference in potential is

required. Different steps and discoveries took place to

come up with Ohm’s law. The main comparison wasbetween electric current in a wire and water in a river

which is now known as the water analogy. In the end

George discovered that how small or large a current is

in a wire does not only depend on the voltage but also

on the resistance the wire offers to the flow of

electrons. This is how he came up with this equation

for the electrical resistance showing that the current isinversely proportional to the resistance.

Furthermore from that equation before he derived

what we know now as Ohm’s law, he found out that in

metal conductors the resistance is a constant

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independent of the voltage and came up with this

formula.

The unit for resistance is called ohm and is

abbreviated by omega (Ω).

Resistors are used to control the amount of current.

These resistors have resistance from less than 1 Ohm

to million of Ohms. The value of a resistance is givenor written on the resistor from the exterior, or may be

given as a color code as shown in the bottom table.

The first two colors represent the first and second

digits, the third color represents the power of ten that

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http://en.wikipedia.org/wiki/Omega




it must be multiplied by, and the fourth is the

manufactured tolerance.

Resistivity

By experiments it was found that the resistance R of

any wire is directly proportional to the length L and

inversely proportional to its cross-sectional area A.

This is how we came up with this rule.

The unit for resistivity is (Ω.m). The resistivity depends

on the material used in the first place then other

factors effect its result such as purity, heat treatment,

temperature and other factors as shown in some of

the materials below.

Discussion

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Electric factors such as electric charge, field, potential,

and current. These discoveries have led to even major

discoveries and developments that we see today. By

using Ohm’s & Coulombs law and understanding theelectric current, electric battery, the different charges

and materials. The derivation of different equations

and formulas to be able to understand the relation

between them such as Current, voltage and resistance

in Ohm’s law and how each one is inversely or directly

proportional to one another.

Conclusion

The discoveries that were mentioned before in the

field of electric charge and electric current have

changed the world as we now it today. With out these

discoveries we wouldn’t have all of this technology

and some of the luxuries we use in our daily lives.Electricity, mobile phones, computers, cars and many

other devices wouldn’t be available nowadays if not

for these discoveries. We should try to improve in the

fields of electric charge and electric current and try to

enhance them to be more efficient to provide a better

living for the future. These discoveries made by

coulomb or ohm and other scientist we found many

years ago. As the years passed the technology andusage of these discoveries have increased rapidly in

addition to having major improvement done to them

and are used in many different fields. This is how

important these finding over the years have affected

our lives as we know now it.

Reference

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DOUGLAS.C.GIANCOLI. PHYSICS: PRINCIPLES WITH APPLICATION, SIXTH

EDITION; Published by: PEARSON EDUCATION, INC: 2005.

http://www.wikipedia.org/

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