Fundamentals of Electricity & Electronics

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Fundamentals of ELECTRICITY & ELECTRONICS

Fundamentals of Electricity

What is Electricity?

Electricity is a naturally occurring force that exists all around us. Humans have beenaware of this force for many centuries. Ancient man believed that electricity was some formof magic because they did not understand it. Greek philosophers noticed that when a pieceof amber was rubbed with cloth, it would attract pieces of straw. They recorded the firstreferences to electrical effects, such as static electricity and lightning, over 2,500 years ago.

It was not until 1600 that a man named Dr. William Gilbert coined the term “electrica,” aLatin word which describes the static charge that develops when certain materials arerubbed against amber. This is probably the source of the word “electricity." Electricity andmagnetism are natural forces that are very closely related to one another. You will learn alittle about magnetism in this section, but there is a whole section on magnetism if youwant to learn more.

In order to really understand electricity, we need to look closely at the very smallcomponents that compose all matter.

Types of electricity

There are two types of Electricity, Static Electricity and Current Electricity. Static Electricityis made by rubbing together two or more objects and making friction while Currentelectricity is the flow of electric charge across an electrical field.

Static Electricity

Static electricity is when electrical charges build up on the surface of a material. It is usuallycaused by rubbing materials together. The result of a build-up of static electricity is thatobjects may be attracted to each other or may even cause a spark to jump from one to theother. For Example rub a baloon on a wool and hold it up to the wall.

Before rubbing, like all materials, the balloons and the wool sweater have a neutral charge.This is because they each have an equal number of positively charged subatomic particles(protons) and negatively charged subatomic particles (electrons). When you rub the balloonwith the wool sweater, electrons are transferred from the wool to the rubber because ofdifferences in the attraction of the two materials for electrons. The balloon becomesnegatively charged because it gains electrons from the wool, and the wool becomespositively charged because it loses electrons.

Current Electricity


Current is the rate of flow of electrons. It is produced by moving electrons and it ismeasured in amperes. Unlike static electricity, current electricity must flow through aconductor, usually copper wire. Current with electricity is just like current when you think ofa river. The river flows from one spot to another, and the speed it moves is the speed ofthe current. With electricity, current is a measure of the amount of energy transferred overa period of time. That energy is called a flow of electrons. One of the results of current isthe heating of the conductor. When an electric stove heats up, it's because of the flow ofcurrent.

There are different sources of current electricity including the chemical reactions takingplace in a battery. The most common source is the generator. A simple generator produceselectricity when a coil of copper turns inside a magnetic field. In a power plant,electromagnets spinning inside many coils of copper wire generate vast quantities ofcurrent electricity.

There are two main kinds of electric current. Direct (DC) and Alternating (AC). It's easy toremember. Direct current is like the energy you get from a battery. Alternating current islike the plugs in the wall. The big difference between the two is that DC is a flow of energywhile AC can turn on and off. AC reverses the direction of the electrons.

Chapter I: COMPOSITION OF MATTER

Composition of Matter

Elements

All matter is composed of atoms. The number of electrons, protons and electrons determinethe properties of those atoms. Matter is made up of elements. Elements are atoms withspecific properties. The main property that defines each elements are the number ofelectrons, proton and neutrons. An example would be that of hydrogen and helium. Both ofthese are elements. The both have electrons, protons, and neutrons but the numbers ofeach are different. That difference alone allow for different chemical and physicalproperties. An element is defined as matter that is made up of the same kind of atoms. Allsodium atoms have the same physical and chemical properties. All nickel elements have thesame chemical and physical properties, although those properties those define each of thepreceding elements are exclusive to those elements alone. There are 111 recognizedelements and they are categorized according to their properties on the Periodic Table.

Compound


A compound is composed of two or more elements of different kinds that are combined.The elements that make up a compound are always composed with the same elements inthe same ratios every time. Glucose is always composed of 6 carbon atoms, 12 hydrogenatoms and 6 oxygen atoms. The properties of a compound are different that the elementsfrom which it is made.

Chemistry is defined as an organized body of knowledge concerning the composition ofmatter and how matter interacts and changes. Matter can be defined as anything thatpossesses the properties of mass and volume. Mass is the measure of a chunk of matter'sability to resist a change in movement or direction. The chemist calls this "inertia". Volumeis the three dimensional space occupied by matter. It is a universal axiom that two chunksof matter can not occupy the same space simultaneously. All matter is composed of basicparticles of atoms, molecules or ions.

What are atoms?

The basic of these particles are the atom. Atoms are particles that are composed ofthree sub-atomic particles. The three sub-atomic particles are the proton, neutron, and theelectron. The proton is a positively charged particle that has the mass approximately equalto a hydrogen atom. It is said to have the mass of 1 atomic mass unit (amu). The protonsreside in the nucleus or center of the atom. The neutron is a neutrally charged particle thatis approximately the mass of a proton. The neutron does not have an electrical charge, butit also resides in the nucleus. The particles of the nucleus are called nucleons. The thirdparticle of an atom is the electron. The electron is a negatively charged particle of negligiblebut finite mass. It resides on the outer edges of the atom with an enormous amount ofspace between the nucleus and the electrons.

Because the protons and the neutrons are relatively well protected in the nucleus and theelectron is on the periphery of the atom, it is the electrons that undergo change during achemical reaction. It is the electrons that the chemist focuses upon. It takes millions oftimes more energy for the nucleus to be penetrated so the nucleus is not affected in normalchemical reactions. Atoms are neutral so that means that the positive protons and thenegative electrons must be equal for the atom to be neutral. There are some 111 knowndifferent atoms that are differentiated by two numbers, atomic number and mass number.The atomic number is equal to the number of protons found in the nucleus. For a neutralatom that would also be the number of electrons in the atom. The mass number is definedas the sum of the protons and the neutrons in the nucleus of an atom. In other words, themass number is the number of nucleons found in the atom. If I know the atomic number ofan atom and the mass number then I can determine the number of electrons, protons, andneutrons that the atom has.


What are molecules?

Molecules are clusters of atoms that are held together by strongelectrical forces called bonds. Molecules are neutral like atoms.Substances that form molecular units are called molecular substances.Just as elements can be symbolized by a symbol, molecules can besymbolized by the symbols of the elements that make up thecompound. These are called formulas. Non-metallic elements react withother non-metallic elements to form molecular compounds

What are ions?

Ions are the third basic particle of matter. Ions are charged atoms or groups of atomspossessing an electrical charge. Atoms are neutral possessing equal numbers of negativeelectrons and positive protons. However some atoms have a tendency to lose one or morenegative electrons during a Chemical change. If the atom loses electrons that would meanthat the atom would have more positive protons than negative electrons and the atomwould become positively charged. These ions are called "cations". Metallic elements tend tolose electrons and become cations.

Other atoms prefer to gain one or more negative electrons. This would give such an atommore negative electrons than protons and the atom would be negatively charged. These arereferred to as "anions". Non-metallic elements have atoms that tend to gain electrons tobecome anions.

Why do atoms lose or gain electrons?

The whole motivation of why some atoms lose and some gain electrons is to make theatoms chemically more stable. They gladly sacrifice their electrical neutrality in favor of amore stable state. The more stable state is an ion that has the same number of electrons asone of the noble gases found in the last column of elements on the right of the periodictable. This condition is referred to as being "isoelectronic" to a Noble gas. These elementsused to be called the "inert gases" because there were no known compounds of theseelements. These elements are still relatively inert which a testament of their great stabilityis. All other elements have atoms that would like to emulate these noble gases. In otherwords, to be isoelectronic to a Noble Gas. The Noble gases were found to react with certainvery chemically reactive elements like Fluorine and Oxygen and only Xenon has been knownto form compounds of Fluorine and Oxygen. It is not surprising that such relatively stableelements would react with these two non-metals (Fluorine and Oxygen) If they were toreact it would be the two most reactive non-metals in the universe.

Why do elements lose or gain different numbers of electrons?

All atoms would like to have the same number of electrons as a Noble gas because of theirgreat stability. In order to accomplish that, some atoms must lose one and some more thanone electron in order to have the same number of electrons as the nearest Noble Gas in the


Periodic Table. For the first column of elements called Group 1 located in the first column onthe left side of the Periodic Table each element in this Group have atoms that have only oneelectron that needs to be lost in order to reach this isoelectronic state with the nearestNoble Gas located on the last column on the extreme right of the Table called Group 18.The second column of elements in the Periodic Table called Group 2 has elements whoseatoms have two electrons that must be lost to become isoelectronic to the nearest NobleGas. On the other end of the Periodic Table, there are Groups of elements like Group 15where atoms must gain three electrons in order to become isoelectronic to the nearestNoble Gas. Group 16 elements have atoms that must gain only two electrons to becomeisoelectronic to the nearest Noble Gas. Group 17 elements which are only one column to theleft of the Noble Gas Group requires that its atoms need only to gain one electron.

Basic Structure of Matter

The Atom

All matter such as solids, liquids, and gases, is composed of atoms. Atoms are almostalways grouped together with other atoms to form what is called a molecule. Only a fewgases such as helium are composed of individual atoms as the structural unit. Therefore,the molecule is considered to be the basic building block of matter.

Atoms are extremely small. The radius of a typical atom is on the order of 0.00000000001meter and cannot be studied without very powerful microscopes.

In the next sub-units you will learn about what a material composed of only one type ofatom is called and you will look at the basic model of an atom.

Elements

An Element defined

Any material that is composed of only one type of atom is called a chemical element, abasic element, or just an element. Any material that is composed of more than one type ofatom is called a compound. Every element has a unique atomic structure. Scientists knowof only about 109 basic elements at this time. (this number has a habit of changing.) Allmatter is composed of combinations of one or more of these elements. Ninety-one of thesebasic elements occur naturally on or in the Earth. The other elements are man-made. Youmay recognize the names of some of these basic elements, such as: hydrogen helium,oxygen, iron, copper, gold, aluminum, uranium. The periodic table of elements (showbelow) lists the basic elements and some of their elements.


ATOM MODELS

What is an atom composed of?

An atom is the smallest particle of any element that still retains the characteristics of thatelement. However, atoms consist of even smaller particles. Atoms consist of a central,dense nucleus that is surrounded by one or more lightweight negatively charged particlescalled electrons. The nucleus is made up of positively charged particles called protons andneutrons which are neutral. An atom is held together by forces of attraction between theelectrons and the protons. The neutrons help to hold the protons together. Protons andneutrons are believed to be made up of even smaller particles called quarks. We will limitour discussions to protons, neutrons and electrons.

Niels Bohr was a Danish scientist who introduced the model of an atom in 1913. Bohr'smodel consists of a central nucleus surrounded by tiny particles called electrons that areorbiting the nucleus in a cloud. These electrons are spinning so fast around the nucleus ofthe atom that they would be just a blur if we could see particles that small. In our picturesand exercises the electron appears to orbit in the same path around the nucleus much likethe planets orbit the Sun. But, please be aware that electrons do not really orbit in thesame path. The electrons actually change their orbit with each revolution.


ELECTRIC CHARGE

Electrons

Electrons are the smallest and lightest of the particles in an atom.Electrons are in constant motion as they circle around the nucleus of thatatom. Electrons are said to have a negative charge, which means thatthey seem to be surrounded by a kind of invisible force field. This is calledan electrostatic field.

Protons

Protons are much larger and heavier than electrons. Protonshave a positive electrical charge. This positively chargedelectrostatic field is exactly the same strength as the electrostaticfield in an electron, but it is opposite in polarity. Notice thenegative electron (pictured at the top left) and the positive proton(pictured at the right) have the same number of force field lines ineach of the diagrams. In other words, the proton is exactly aspositive as the electron is negative.

Like charges repel, unlike charges attract

Two electrons will tend to repel each other because both have a negative electrical charge.Two protons will also tend to repel each other because they both have a positive charge. Onthe other hand, electrons and protons will be attracted to each other because of their unlikecharges.

Since the electron is much smaller and lighter than a proton, when they are attracted toeach other due to their unlike charges, the electron usually does most of the moving. This isbecause the protons have more mass and are harder to get moving. Although electrons arevery small, their negative electrical charges are still quite strong. Remember, the negativecharge of an electron is the same as the positive electrical charge of the much larger in sizeproton. This way the atom stays electrically balanced.

Another important fact about the electrical charges of protons and electrons is that thefarther away they are from each other, the less force their electric fields have on eachother. Similarly, the closer they are to each other, the more force they will experience fromeach other due to this invisible force field called an electric field.


THE FREE ELECTRON

Maintaining electrical balance

Each basic element has a certain number of electrons and protons, which distinguishes eachelement from all other basic elements. In most elements, the number of electrons is equalto the number of protons. This maintains an electrical balance in the structure of atomssince protons and electrons have equal, but oppositeelectrostatic fields.

Pictured here is an atom of copper, which is much more complex than either an atom ofhydrogen or helium.

The copper atom has 29 protons in its nucleus with 29 electrons orbiting the nucleus. Noticethat in the copper atom, the electrons are arranged in several layers called shells. This isto graphically represent that the electrons are at different orbits or energy levels within theatom. The energy of an electron is restricted to a few particular energy levels. The energy issaid to be quantized, meaning that it cannot vary continuously over a range, but instead islimited to certain values. These energy levels or shells follow a very predictable pattern. Theclosest shell to the nucleus can have up to 2 electrons. The second shell from the nucleuscan have up to 8 electrons. The third shell can have up to 18 electrons. The fourth shell canhave up to 32 electrons, and so on. Atoms can have this many electrons, but they do nothave to have this many electrons in each shell. The greater distance between the electronsin the outer shells and the protons in the nucleus mean the outer shell electrons experienceless of a force of attraction to the nucleus than do the electron in the inner shells.

In the next sub-unit you will learn about the the outer shell of an atom called the valenceshell.

THE VALENCE SHELL

What is the valence shell?


Notice that in the copper atom pictured below that the outside shell has only one electron.This represents that the copper atom has one electron that is near the outer portion of theatom. The outer shell of any atom is called the valence shell. When the valence electron inany atom gains sufficient energy from some outside force, it can break away from theparent atom and become what is called a free electron.

Pictured here is an atom of copper, which is much more complex than either anatom of hydrogen or helium.

Atoms with few electrons in their valence shell tend to have more free electrons since thesevalence electrons are more loosely bound to the nucleus. In some materials like copper, theelectrons are so loosely held by the atom and so close to the neighboring atoms that it isdifficult to determine which electron belongs to which atom. Under these conditions, thevalence or free electrons tend to drift randomly from one atom to its neighboring atoms.Under normal conditions the movement of the electrons is truly random, meaning they aremoving in all directions by the same amount. However, if some outside force acts upon thematerial, this flow of electrons can be directed through materials and this flow is calledelectrical current. Materials that have free electrons and allow electrical current to floweasily are called conductors. Many materials do not have any free electrons. Because ofthis fact, they do not tend to share their electrons very easily and do not make goodconductors of electrical currents. These materials are called insulators. There will be moreinformation on this later.

Chapter II: SOURCES OF ELECTRICITY, CHARGES, AND STATIC ELECTRICITY

Static Electricity

Static electricity is an electric charge built up on persons or objects through friction. It ismost familiar as an occasional annoyance in seasons of low humidity, but can bedestructive and harmful in some situations. When working in direct contact with integrated


circuits electronics, or in the presence of flammable gas, care must be taken to avoidaccumulating and discharging static electricity.

Static electricity is electricity that does not flow in a current. Static electricity is generatedby rubbing two nonmagnetic objects together. The friction between the two objectsgenerates attraction because the substance with an excess of electrons transfers them tothe positively-charged substance. Usually, substances that don't conduct current electricity(insulators) are good at holding a charge. These substances may include rubber, plastic,glass or pitch. The electrons that are transferred are stored on the surface of an object.

Materials Causing Charges

Static electricity is created by putting certain materials together and then pulling themapart causes excess electrical charges to be created on their surfaces. This can be done bypushing them together and pulling them apart or by rubbing the materials together, whichis the main way it is created.

Excess Of Charges

Most matter is electrically neutral. That means its atoms and molecules have the samenumber of electrons as protons. If a material somehow obtains extra electrons and attachesthem to the atom's outer orbits or shells, that material has a negative ( - ) charge.Likewise, if a material loses electrons, it has an excess of positive (+) charges. The electricfield from the excess of charges then causes the electric effects of attraction, repulsion or aspark (lightning).

Stealing Electrons

According to Solar System Model (or Bohr Model) of the atom, electrons are in orbits orshells around the nucleus. A maximum number of electrons are allowed in each orbit.Forces in each atom seek to reach that maximum number, such that if an element is justone electron short of the maximum amount in its outer orbit, it would try to "steal" anelectron from another element that may be just starting its outer orbit. This is the basis ofchemical reactions.

Adhesive Molecular Force

That force will also tend to hold two different materials together. In that situation, the forceis called the adhesive molecular force. When different materials are pressed together andthen pulled apart, the adhesive molecular force pulls electrons from material unto the other.This creates the phenomenon.

You can see this effect with a piece of Scotch tape or similar tape. First verify that it is notattracted to your finger. Then stick it to some surface and then pull it off. Put you finger


near the tape and it will now be attracted to your finger, showing that there is an excess ofcharges on the tape.

Despite their small size, protons and electrons carry an electrical charge. Protons carry a"positive" charge, while electrons carry a "negative" energy charge.

Usually, the two different charges balance each other out, and nothing happens. But whentwo objects with like charges (all positive or all negative) come together, the charges repeland the objects move away from each other. Objects with opposite charges attract eachother because the different charges want to enter a state of balance with each other.

Objects can get a negative charge by picking up electrons from other objects. For example,when your shoes scuff against the rug, your shoes are actually picking up electrons fromthe rug. The electrons fly over your body, giving you a negative charge.

Your new electrons fly over your body because they are looking for a positive charge. If youtouch a metal doorknob, the electrons on your body will leap into the metal, attracted bythe protons there. The transfer of electrons is actually a small electrical current, andproduces the tiny electric shock you feel.

Lightning is similar, except on a much bigger scale. Both lightning and static electricityhappens because of the attraction between the opposite charges.

Not friction

Although your can create it by pressing materials together and pulling them apart, rubbingthem together works even better, except in the case of something sticky like tape.

One unfortunate result from saying that rubbing materials creates this phenomenon is thatmost people think that friction causes the charges to build up. It is not friction that causesthe spark, rather it is the adhesive forces that pull off electrons.

Dry human skin and rabbit fur have the greatest tendency to give up electrons whenrubbed on something and become positively ( + ) charged. Teflon and vinyl have thegreatest tendency to become negatively charged ( - ) when rubbed. If you want to create acharge, rubbing fur on teflon should give the best results.


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Fundamentals of Electricity & Electronics