3. Electrical Fundamental

8/11/2019 3. Electrical Fundamental

1/926

Integrated Training SystemDesigned in association with the

club66pro.co.uk question practice aid

Module 3

Electrical undamentals!or

E"S" #art$66

%icence &ategory'( and ')


2/926



#re!ace

Thank you !or purchasing the Total Training Support Integrated Training System. *e are sureyou will need no other re!erence material to pass your E"S" #art$66 e+am in this Module.

,

%

-

These notes hae been written by instructors o! E"S" #art$66 courses/ speci!ically !or

practitioners o! arying e+perience within the aircra!t maintenance industry/ and especially those

who are sel!$studying to pass the E"S" #art$66 e+ams. They are speci!ically designed to meet theE"S" #art$66 syllabus and to answer the questions being asked by the ,0 &"" in their

e+aminations.

The E"S" #art$66 syllabus !or each sub$section is printed at the beginning o! each o! the

chapters in these course notes and is used as the 1%earning 2becties1.

(, *e suggest that you take each chapter in$turn/ read the te+t o! the chapter a couple o! times/ i!

only to !amiliarise yoursel! with the location o! the in!ormation contained within. Then/ using

your club66pro.co.uk membership/ attempt the questions within the respectie sub$section/

%i and continually re!er back to these notes to read$up on the underpinning knowledge required toanswer the respectie question/ and any similar question that you may encounter on your real

#art$66 e+amination. Studying this way/ with the help o! the question practice and their

%i e+planations/ you will be able to master the subect piece$by$piece/ and become pro!icient in thesubect matter/ as well as pro!icient in answering the &"" style E"S" part$66 multiple choicequestions.

%

*e regularly hae a reiew o! our training notes/ and in order to improe the quality o! the

notes/ and o! the serice we proide with our Integrated Training System/ we would appreciate

your !eedback/ whether positie or negatie.

So/ i! you discoer within these course notes/ any errors or typos/ or any subect which is not

particularly well/ or adequately e+plained/ please tell us/ using the 4contact$us5 !eedback page o! the

club66pro.co.uk website. *e will be sure to reiew your !eedback and incorporate any changesnecessary. *e look !orward to hearing !rom you.

inally/ we appreciate that sel!$study students are usually also sel!$!inancing. *e work eryhard to cut the cost o! our Integrated Training System to the bare minimum that we can proide/ and

in making your training resources as cost e!!icient as we can/ using/ !or e+ample/ monoprinting/ but proiding the diagrams which would be better proided in colour/ on the

club66pro.co.uk website. In order to do this/ we request that you respect our copyright policy/ and

re!rain !rom copying/ scanning or reprinting these course notes in any way/ een !or sharing with!riends and colleagues. 2ur surial as a serice proider depends on it/ and copyright abuse only

dealues the serice and products aailable to yoursel! and your colleagues in the

!uture/ and makes them more e+pensie too.

Exclusively from

www.airtechbooks.con


3/926

Module 3 #re!ace ITTS Integrated Training System

&opyright )7(7


4/926



n

Intentionally 'lank

8%

IIModule 3 #re!ace

TTS Integrated Training System &opyright )7(7


5/926



:

Module 3 &hapters

(. Electron Theory

).Static Electricity and &onduction! 3.Electrical Terminology

;. ? 6.D& &ircuits

8.@esistanceA@esistor

B.#owerr 5 C.&apacitanceAcapacitor, (7.Magnetism

((.InductanceAinductor().D& MotorA


6/926

&opyright )7(7


7/926



Intentionally 'lank

iModule 3 #re!ace

TTS Integrated Training System &opyright )7(7


8/926

w 5 Integrated Training SystemDesigned in association with the


TTS Integrated

Training System

Module 3

%icence &ategory '(A')

Electrical undamentals

3.( Electron Theory

Module 3.( Electron Theory ($(,se andAor disclosure is TTS Integrated Training Systemgoerned by the statement


9/926

./.. $$ 7 o! thie r.han!ar


10/926



&opyright Gotice

&opyright. "ll worldwide rights resered. Go part o! this publication may be reproduced/ stored

in a retrieal system or transmitted in any !orm by any other means whatsoeerH i.e.photocopy/

electronic/ mechanical recording or otherwise without the prior written permission o! Total TrainingSupport %td.

0nowledge %eels $ &ategory "/ '(/ ') and & "ircra!t Maintenance%icence

'asic knowledge !or categories "/ (3( and ') are indicated by the allocation o! knowledge leels indicators (/ ) or3 against each applicable subect. &ategory & applicants must meet either the category '( or the category ')

basic knowledge leels.

The knowledge leel indicators are de!ined as !ollowsH

%EE% (J " !amiliarisation with the principal elements o! the subect.

2bectiesH

J The applicant should be !amiliar with the basic elements o! the subect.

J The applicant should be able to gie a simple description o! the whole subect/ using common words ande+amples.

J The applicant should be able to use typical terms.

%EE% )

J " general knowledge o! the theoretical and practical aspects o! the subect.J "n ability to apply that knowledge.

2bectiesHJ The applicant should be able to understand the theoretical !undamentals o! the subect.

J The applicant should be able to gie a general description o! the subect using/ as appropriate/ typicale+amples.

J The applicant should be able to use mathematical !ormulae in conunction with physical laws describing thesubect.

J The applicant should be able to read and understand sketches/ drawings and schematics describing thesubect.

J The applicant should be able to apply his knowledge in a practical manner using detailed procedures.

%EE% 3J " detailed knowledge o! the theoretical and practical aspects o! the subect.

J " capacity to combine and apply the separate elements o! knowledge in a logical and comprehensiemanner.

2bectiesH

J The applicant should know the theory o! the subect and interrelationships with other subects.

J The applicant should be able to gie a detailed description o! the subect using theoretical !undamentalsand speci!ic e+amples.

J The applicant should understand and be able to use mathematical !ormulae related to the subect.

J The applicant should be able to read/ understand and prepare sketches/ simple drawings and schematicsdescribing the subect.

J The applicant should be able to apply his knowledge in a practical manner using manu!acturer5sinstructions.

J The applicant should be able to interpret results !rom arious sources and measurements and apply

correctie action where appropriate.

($)

t (

LJ

I

Module 3.( Electron Theory ,se andAor disclosure isTTS Integrated Training System goerned by the statement &opyright )7(7 on page ) o! this &hapter.


11/926



Table o! &ontents

Module 3.( Electron Theory =Matter =

Elements and &ompounds =

Molecules =

"toms =

9 Energy %eels B% Shells and Sub$shells C

alence ((

&ompounds ((

Ionisation ((

&onductors/ Semiconductors/ and Insulators ((

%

%

,

Module 3.( Electron Theory ($3,se andAor disclosure is TTS Integrated Training Systemgoerned by the statement


12/926

on page ) o! this &hapter. &opyright )7(7


13/926



Module 3.( Enabling 2becties

2bectie E"S" 66 @e!erence %eel

Electron Theory 3.( (Structure and distribution o! electrical charges withinHatoms/ molecules/ ions/ compounds

! l

($;

TTS Integrated Training SystemModule 3.( Electron Theor

y ,se andAor disclosure is

goerned by the statement &opyright )7(7 on page ) o! this &hapter.


14/926


club66pio.co.uk question practice aid

Module 3.( Electron Theory

Matter

Matter is de!ined as anything that occupies space and has weightK that is/ the weight and

dimensions o! matter can be measured. E+amples o! matter are air/ water/ automobiles/

clothing/ and een our own bodies. Thus/ we can say that matter may be !ound in any one o!three statesH solid/ liquid/ and gaseous.

Elements and &ompounds

"n E%EMEGT is a substance which cannot be reduced to a simpler substance by chemical

means. E+amples o! elements with which you are in eeryday contact are iron/ gold/ siler/copper/ and o+ygen. There are now oer (77 known elements. "ll the di!!erent substances weknow about are composed o! one or more o! these elements.

*hen two or more elements are chemically combined/ the resulting substance is called acompound. " compound is a chemical combination o! elements which can be separated by

(

r

%

chemical but not by physical means. E+amples o! common compounds are water whichconsists o! hydrogen and o+ygen/ and table salt/ which consists o! sodium and chlorine. "

mi+ture/ on the other hand/ is a combination o! elements and compounds/ not chemicallycombined/ that can be separated by physical means. E+amples o! mi+tures are air/ which is

made up o! nitrogen/ o+ygen/ carbon dio+ide/ and small amounts o! seeral rare gases/ and sea

water/ which consists chie!ly o! salt and water.

Molecules

" molecule is a chemical combination o! two or more atoms/ atoms are described in the ne+t

paragraph. In a compound the molecule is the smallest particle that has all the characteristics o!

the compound.

&onsider water/ !or e+ample. *ater is matter/ since it occupies space and has weight.

Depending on the temperature/ it may e+ist as a liquid water/ a solid ice/ or a gas steam.

@egardless o! the temperature/ it will still hae the same composition. I! we start with a quantityo! water/ diide this and pour out one hal!/ and continue this process a su!!icient number o!

times/ we will eentually end up with a quantity o! water which cannot be !urther diided without

ceasing to be water. This quantity is called a molecule o! water. I! this molecule o! water

diided/ instead o! two parts o! water/ there will be one part o! o+ygen and two parts o!

hydrogen L)7.

"toms

Molecules are made up o! smaller particles called atoms. "n atom is the smallest particle o! anelement that retains the characteristics o! that element. The atoms o! one element/ howeer/ di!!er

!rom the atoms o! all other elements. Since there are oer (77 known elements/ theremust be oer (77 di!!erent atoms/ or a di!!erent atom !or each element. :ust as thousands o!

($=

,se andAor disclosure isModule 3.( Electron Theory

TTS Integrated Training System


15/926

goerne y t e statement



16/926

Integrated Training System

Designed in association with the nclub66pro.co.uk question practice aid

words can be made by combining the proper letters o! the alphabet/ so thousands o! di!!erent

materials can be made by chemically combining the proper atoms. :

"ny particle that is a chemical combination o! two or more atoms is called a molecule. The

o+ygen molecule consists o! two atoms o! o+ygen/ and the hydrogen molecule consists o! twoatoms o! hydrogen. Sugar/ on the other hand/ is a compound composed o! atoms o! carbon/

hydrogen/ and o+ygen. These atoms are combined into sugar molecules. Since the sugarmolecules can be broken down by chemical means into smaller and simpler units/ we cannothae sugar atoms.

The atoms o! each element are made up o! electrons/ protons/ and/ in most cases/ neutrons/which are collectiely called subatomic particles. urthermore/ the electrons/ protons/ and

neutrons o! one element are identical to those o! any other element. The reason that there are

di!!erent kinds o! elements is that the number and the arrangement o! electrons and protonswithin the atom are di!!erent !or the di!!erent elements

The electron is considered to be a small negatie charge o! electricity. The proton has a positiecharge o! electricity equal and opposite to the charge o! the electron. Scientists hae measuredthe mass and sie o! the electron and proton/ and they know how much charge each

possesses. The electron and proton each hae the same quantity o! charge/ although the masso! the proton is appro+imately (B38 times that o! the electron. In some atoms there e+ists aneutral particle called a neutron. The neutron has a mass slightly greater than that o! a proton/but it has no electrical charge. "ccording to a popular theory/ the electrons/ protons/ andneutrons o! the atoms are thought to be arranged in a manner similar to a miniature solarsystem. The protons and neutrons !orm a heay nucleus with a positie charge/ around whichthe ery light electrons reole.

igure (.( shows one hydrogen and one helium atom. Each has a relatiely simple structure.The hydrogen atom has only one proton in the nucleus with one electron rotating about it. Thehelium atom is a little more comple+. It has a nucleus made up o! two protons and two neutrons/ Iwith two electrons rotating about the nucleus. Elements are classi!ied numerically according tothe comple+ity o! their atoms. The atomic number o! an atom is determined by the number o!protons in its nucleus.

n

($6 Module 3.( Electron Theory ,se antllor disclosure isTTS Integrated Training System goerned the &opyright )7(7 on page ) o! this &hapter.


17/926



((

(5I./NOI,I4:5

E%E&T@2G S c$:

I

LPD@2


18/926

on page ) o! this &hapter. opyr g t


19/926



Energy %eels

Since an electron in an atom has both mass and motion/ it contains two types o! energy. 'y

irtue o! its motion the electron contains kinetic energy. Due to its position it also contains

potential energy. The total energy contained by an electron kinetic plus potential is the !actorwhich determines the radius o! the electron orbit. In order !or an electron to remain in this orbit/ it

must neither


20/926



period o! time the electron may ump back to the !irst leel emitting a new photon identical to theone it receied.

" second alternatie would be !or the electron to return to the lower leel in two umpsK !rom the

third to the second/ and then !rom the second to the !irst. In this case the electron would emit twophotons/ one !or each ump. Each o! these photons would hae less energy than the

original photon which e+cited the electron.

This principle is used in the !luorescent light where ultraiolet light photons/ which are not isible to

the human eye/ bombard a phosphor coating on the inside o! a glass tube. The phosphor electrons/

in returning to their normal orbits/ emit photons o! light that are isible. 'y using the proper

chemicals !or the phosphor coating/ any colour o! light may be obtained/ including white.

This same principle is also used in lighting up the screen o! a teleision picture tube.

The basic principles ust deeloped apply equally well to the atoms o! more comple+ elements. Inatoms containing two or more electrons/ the electrons interact with each other and the e+act%: path o! any one electron is ery di!!icult to predict. Loweer/ each electron lies in a speci!ic

energy band and the orbits will be considered as an aerage o! the electron5s position.

Shells and Sub$shells

The di!!erence between the atoms/ inso!ar as their chemical actiity and stability are concerned/ is

dependent upon the number and position o! the electrons included within the atom. Low are theseelectrons positioned within the atom? In general/ the electrons reside in groups o! orbits calledshells. These shells are elliptically shaped and are assumed to be located at !i+ed

interals. Thus/ the shells are arranged in steps that correspond to !i+ed energy leels. Theshells/ and the number o! electrons required to !ill them/ may be predicted by the employment o!

#auli5s e+clusion principle. Simply stated/ this principle speci!ies that each shell will contain a

ma+imum o! )n) electrons/ where n corresponds to the shell number starting with the one

closest to the nucleus. 'y this principle/ the second shell/ !or e+ample/ would contain )) )or B

electrons when !ull.

In addition to being numbered/ the shells are also gien letter designations/ as pictured in !igure ($3.

Starting with the shell closest to the nucleus and progressing outward/ the shells are labelled 0/ %/

M/ G/ 7/ #/ and / respectiely. The shells are considered to be !ull/ or complete/ when they contain

the !ollowing quantities o! electronsH two in the 0 shell/ eight in the % shell/ (B in the M shell/ and so

on/ in accordance with the e+clusion principle.

Each o! these shells is a maor shell and can be diided into sub$shells/ o! which there are !our/

labelled s/ p/ d/ and !. %ike the maor shells/ the sub$shells are also limited as to the number o!

electrons which they can contain. Thus/ the 1s1 sub$shell is complete when it contains two

electrons/ the 1p1 sub$shell when it contains 6/ the 1d1 sub$shell when it contains (7/ and the 1!1

sub$shell when it contains (; electrons.

Module 3.( Electron Theory ($C,se andAor disclosure is TTS Integrated Training Systemgoerned by the statement


21/926



22/926



LETTERDESI


23/926



alence

The number o! electrons in the outermost shell determines the alence o! an atom. or this

reason/ the outer shell o! an atom is called the alence shellK and the electrons contained inthis shell are called alence electrons. The alence o! an atom determines its ability to gain orlose an electron/ which in turn determines the chemical and electrical properties o! the atom. "n

atom that is lacking only one or two electrons !rom its outer shell will easily gain electrons to

complete its shell/ but a large amount o! energy is required to !ree any o! its electrons. "n atom

haing a relatiely small number o! electrons in its outer shell in comparison to the number o!

electrons required to !ill the shell will easily lose these alence electrons. The alence shell

always re!ers to the outermost shell.

&ompounds

#ure substances made up more than ( element which hae been oined together by a chemical

,

,

$ /

t,

reaction there!ore the atoms are di!!icult to separate. The properties o! a compound are di!!erent

!rom the atoms that make it up. Splitting o! a compound is called chemical analysis.

Gote that a compoundH

J consists o! atoms o! two or more di!!erent elementsbound together,J can be broken down into a simpler type o! matter elements by chemical means but not

by physical means/

J has properties that are di!!erent !rom its component elements/ andJ always contains the same ratio o! its component atoms.

Ionisation

*hen the atom loses electrons or gains electrons in this process o! electron e+change/ it is said tobe ionied. or ionisation to take place/ there must be a trans!er o! energy which results in achange in the internal energy o! the atom. "n atom haing more than its normal amount o!

electrons acquires a negatie charge/ and is called a negatie ion. The atom that gies up

some o! its normal electrons is le!t with less negatie charges than positie charges and is

called a positie ion. Thus/ ionisation is the process by which an atom loses or gains electrons.

&onductors/ Semiconductors/ and Insulators

In this study o! electricity and electronics/ the association o! matter and electricity is important.

Since eery electronic deice is constructed o! parts made !rom ordinary matter/ the e!!ects o!

electricity on matter must be well understood. "s a means o! accomplishing this/ all elements o!

which matter is made may be placed into one o! three categoriesH conductors/semiconductors/ and insulators/ depending on their ability to conduct an electric current.conductors are elements which conduct electricity ery readily/ insulators hae an e+tremelyhigh resistance to the !low o! electricity. "ll matter between these two e+tremes may be called

semiconductors.

($((Module 3.( Electron Theory

,se andAor disclosure is TTS Integrated Training Systemgoerned by the statement


24/926



25/926



The electron theory states that all matter is composed o! atoms and the atoms are composed o!

smaller particles called protons/ electrons/ and neutrons. The electrons orbit the nucleus which

contains the protons and neutrons. It is the alence electrons the electrons in the outer shell

that we are most concerned with in electricity. These are the electrons which are easiest to

break loose !rom their parent atom. Gormally/ conductors hae three or less alence electronsKinsulators hae !ie or more alence electronsK and semiconductors usually hae !our alence

electrons. The !ewer the alence electrons/ the better conductor o! electricity it will be. &opper/ n5n!or e+ample/ has ust one alence electron.

The electrical conductiity o! matter is dependent upon the atomic structure o! the material !rom

which the conductor is made. In any solid material/ such as copper/ the atoms which make upthe molecular structure are bound !irmly together. "t room temperature/ copper will contain a

considerable amount o! heat energy. Since heat energy is one method o! remoing electrons !rom

their orbits/ copper will contain many !ree electrons that can moe !rom atom to atom. *hen not

under the in!luence o! an e+ternal !orce/ these electrons moe in a haphaard

manner within the conductor. This moement is equal in all directions so that electrons are not lostor gained by any part o! the conductor. *hen controlled by an e+ternal !orce/ the electrons moe

generally in the same direction. The e!!ect o! this moement is !elt almost instantly !rom one end o!the conductor to the other. This electron moement is called an electric current.

Some metals are better conductors o! electricity than others. Siler/ copper/ gold/ and

aluminium are materials with many !ree electrons and make good conductors. Siler is the bestconductor/ !ollowed by copper/ gold/ and aluminium. &opper is used more o!ten than silerbecause o! cost. "luminium is used where weight is a maor consideration/ such as in hightensionpower lines/ with long spans between supports.


26/926



!

% "tomic Element Electrons per Shell "tomic Element Electrons per ShellGo. Go.

0%MG2# 0%MG 7 #( Lydrogen I =3 Iodine ) B (B B 8

% ) Lelium ) =; Uenon ) B (B (B B3 %ithium ) ( == &esium ) B (B B B (; 'eryllium ) ) =6 'arium ) B (B B B )

= 'oron ) 3 =8 %anthanum ) B (B B C )

6 &arbon ) ; =B &erium ) B (B (C C )

8 Gitrogen ) = =C #raseodymium ) B (B )7 C )

B 2+ en ) $67 $ Geodymium ) B (B )( C )

C luorine ) 6( #romethium ) B (B )) C )

(7 Geon ) 6) Samarium ) B (B )3 C )

(( Sodium ) 63 Europium ) S (B ); C )

() Magnesium ) 6;


27/926

goerne y t e statement



28/926



5. :

Li

:

Intentionally 'lank

($(;Module 3.( Electron Theory ,se andAor disclosure is

TTS Integrated Training Systemgoerned by the statement

&opyright )7(7 on page ) o! this &hapter.


29/926

cub66pro.co.uk question!ractice aid

TTS IntegratedTraining System

Module 3

%icence &ategory'(A6)


3.) Static Electricity and &onduction

)$(

Module 3.) Static Electricity and &onduction TTS integrated Training System !$$$


30/926


31/926



&opyright Gotice

Total Training Support %td. T

%icence



%EE% 8

2bectiesH

J

Je+amples.


%EE% )

J "n ability to apply that knowledge.2bectiesH

J



Jsubect.


%EE% 3

J

J " capacity to combine and apply the separate elements o! knowledge in a logical and comprehensiemanner.

2bectiesH

J

and speci!ic e+amples.

J



J The applicant should be able to interpret results !rom arious sources and measurements and applycorrectie action where appropriate.

)$)Module 3.) Static Electricity and &onduction

TTS Integrated Training System ,se andAor disclosure isgoerned by the statement



32/926


, club66pro.co.uk question practice aid

Table o! &ontents

Module 3.) Static Electricity and &onduction =Introduction =Static Electricity 6Gature o! &harges 8

&harged 'odies 8

&oulomb5s %aw o! &harges B

,nit o! &harge B

Electric ields B

&onduction o! Electricity in Solids/ %iquids and a acuum C

%i

%

u

%

Module 3.) Static Electricity and &onduction )$3,se andAor disclosure Is

goerned by the statement TTS Integrated Training SystemiT


33/926



34/926



Module 3.) Enabling 2becties

2bectie E"S" 66 @e!erence %eel

Static Electricity and &onduction 3.) )Static electricity and distribution o! electrostatic charges

Electrostatic laws o! attraction and repulsion

,nits o! charge/ &oulomb5s %aw

&onduction o! electricity in solids/ liquids/ gases and aacuum

i:

t i

)$;Module 3.) Static Electricity and &onduction

,se andAor disclosure is

TTS Integrated Training System goerned by the statement &opyright )7(7 on page ) o! this &hapter.


35/926



%

Module 3.) Static$ Electricity and &onduction

Introduction

Electrostatics electricity at rest is a subect with which most persons entering the !ield o!electricity and electronics are somewhat !amiliar. or e+ample/ the way a person5s hair standson end a!ter a igorous rubbing is an e!!ect o! electrostatics. *hile pursuing the study o!

electrostatics/ you will gain a better understanding o! this common occurrence. 2! een greater

signi!icance/ the study o! electrostatics will proide you with the opportunity to gain important

background knowledge and to deelop concepts which are essential to the understanding o!%l electricity and electronics.

/

Interest in the subect o! static electricity can be traced back to the


36/926



37/926



Static Electricity

In a natural or neutral state/ each atom in a body o! matter will hae the proper number o!

electrons in orbit around it. &onsequently/ the whole body o! matter composed o! the neutral atoms

will also be electrically neutral. In this state/ it is said to hae a 1ero charge.1 Electrons will neitherleae nor enter the neutrally charged body should it come in contact with other

neutral bodies. I!/ howeer/ any number o! electrons is remoed !rom the atoms o! a body o! matter/

there will remain more protons than electrons and the whole body o! matter will become electrically

positie. Should the positiely charged body come in contact with another body haing a normal

charge/ or haing a negatie too many electrons charge/ an electric current will !low between

them. Electrons will leae the more negatie body and enter the positie body. This electron !low

will continue until both bodies hae equal charges. *hen two bodies o!

matter hae unequal charges and are near one another/ an electric !orce is e+erted between thembecause o! their unequal charges. Loweer/ since they are not in contact/ their chargescannot equalie. The e+istence o! such an electric !orce/ where current cannot !low/ is re!erred to

as static electricity. 1Static1 in this instance means 1not moing.1 It is also re!erred to as anelectrostatic !orce.

2ne o! the easiest ways to create a static charge is by !riction. *hen two pieces o! matter arerubbed together/ electrons can be 1wiped o!!1 one material onto the other. I! the materials used aregood conductors/ it is quite di!!icult to obtain a detectable charge on either/ since equaliing

currents can !low easily between the conducting materials. These currents equalie the chargesalmost as !ast as they are created. " static charge is more easily created between non$conducting materials. *hen a hard rubber rod is rubbed with !ur/ the rod will accumulate

electrons gien up by the !ur/ as shown in !igure ).(. Since both materials are poor conductors/ery little equaliing current can !low/ and an electrostatic charge builds up. *hen the charge

becomes great enough/ current will !low regardless o! the poor conductiity o! the materials. Thesecurrents will cause isible sparks and produce a crackling sound.

W&L"@


38/926



Gature o! &harges

*hen in a natural or neutral state/ an atom has an equal number o! electrons and protons.

'ecause o! this balance/ the net negatie charge o! the electrons in orbit is e+actly balanced bythe net positie charge o! the protons in the nucleus/ making the atom electrically neutral.

"n atom becomes a positie ion wheneer it loses an electron/ and has an oerall positiecharge. &onersely/ wheneer an atom acquires an e+tra electron/ it becomes a negatie ionand has a negatie charge.

Due to normal molecular actiity/ there are always ions present in any material. I! the number o!

positie ions and negatie ions is equal/ the material is electrically neutral. *hen the number o!

positie ions e+ceeds the number o! negatie ions/ the material is positiely charged. Thematerial is negatiely charged wheneer the negatie ions outnumber the positie ions.

Since ions are actually atoms without their normal number o! electrons/ it is the e+cess or the lacko! electrons in a substance that determines its charge. In most solids/ the trans!er o!charges is by moement o! electrons rather than ions. The trans!er o! charges by ions will

become more signi!icant when we consider electrical actiity in liquids and gases. "t this time/ we

will discuss electrical behaiour in terms o! electron moement.

&harged 'odies

2ne o! the !undamental laws o! electricity is that like charges repel each other and unlikecharges attract each other. " positie charge and negatie charge/ being unlike/ tend to moe

ri toward each other. In the atom/ the negatie electrons are drawn toward the positie protons in

%?l the nucleus. This attractie !orce is balanced by the electron5s centri!ugal !orce caused by itsrotation about the nucleus. "s a result/ the electrons remain in orbit and are not drawn into thenucleus. Electrons repel each other because o! their like negatie charges/ and protons repeleach other because o! their like positie charges.

$/ The law o! charged bodies may be demonstrated by a simple e+periment. Two pith paper pulp

%i balls are suspended near one another by threads/ as shown in !igure ).).

$/

' &igure ).) $ @epulsion and attraction o! charged bodies

)$8

,se andAor disclosure is Module 3.) Static Electricity and &onduction


39/926

goerned by the statement ntegrate ra n ng ystemon page ) o! this &hapter. &opyright )7(7


40/926

Integrated Training System nDesigned in association with the


I! a hard rubber rod is rubbed with !ur to gie it a negatie charge and is then held against the

right$hand ball in part "/ the rod will gie o!! a negatie charge to the ball. The right$hand ball will

hae a negatie charge with respect to the le!t$hand ball. *hen released/ the two balls willbe drawn

together/ as shown in !igure ).) ". They will touch and remain in contact until the le!t$hand ball

gains a portion o! the negatie charge o! the right$hand ball/ at which time they will swing apart asshown in !igure ).) &. I! a positie or a negatie charge is placed on both balls !igure )$) '/

the balls will repel each other.

&oulomb5s %aw o! &harges

The relationship between attracting or repelling charged bodies was !irst discoered and written

about by a rench scientist named &harles ". &oulomb. &oulomb5s %aw states that

&harged bodies attract or repel each other with a !orce that is directly proportional to theproduct o! their indiidual charges/ and is inersely proportional to the square o! the

distance between them.

The amount o! attracting or repelling !orce which acts between two electrically charged bodies in!ree space depends on two things $ ( their charges and ) the distance between them.

,nit o! &harge

The process o! electrons arriing or leaing is e+actly what happens when certain combinationso! materials are rubbed togetherH electrons !rom the atoms o! one material are !orced by therubbing to leae their respectie atoms and trans!er oer to the atoms o! the other material. In

other words/ electrons comprise the 1!luid1 hypothesied by 'enamin ranklin. The operationalde!inition o! a coulomb as the unit o! electrical charge in terms o! !orce generated betweenpoint charges was !ound to be equal to an e+cess or de!iciency o! about6/)B7/777/777/777/777/777 electrons. 2r/ stated in reerse terms/ one electron has a charge o!about 7.777777777777777777(6 coulombs. 'eing that one electron is the smallest knowncarrier o! electric charge/ this last !igure o! charge !or the electron is de!ined as the elementarycharge.

n

( coulomb R 6/)B7/777/777/777/777/777 electrons

Electric ields

The space between and around charged bodies in which their in!luence is !elt is called anelectric !ield o! !orce. It can e+ist in air/ glass/ paper/ or a acuum. electrostatic !ields anddielectric !ields are other names used to re!er to this region o! !orce.ields o! !orce spread out in the space surrounding their point o! origin and/ in general/

diminish in proportion to the square o! the distance !rom their source.

The !ield about a charged body is generally represented by lines which are re!erred to as

electrostatic lines o! !orce. These lines are imaginary and are used merely to represent thedirection and strength o! the !ield. To aoid con!usion/ the lines o! !orce e+erted by a positie

charge are always shown leaing the charge/ and !or a negatie charge they are shown

entering. igure ).3 illustrates the use o! lines to represent the !ield about charged bodies.

)$B Module 3.) Static Electricity and &onduction,se andlor disclosure is

TTS Integrated Training System goerned by the statement &opyright )7(7 on page ) o! this &hapter.


41/926



!

,

"

'

igure ).3 $ Electrostatic lines o! !orce

,igure ).3 " represents the repulsion o! like$charged bodies and their associated !ields. #art

' represents the attraction o! unlike$charged bodies and their associated !ields.

r &onduction o! Electricity in Solids/ %iquids and a acuum

Solids

( Electric current is the moement o! alence electrons. &onduction is the name o! this process., It is more !ully described in &hapter ( o! this Module.


42/926

goerned by the statement ntegrate ra n ng ystemon page ) o! this &hapter. &opyright )7(7


43/926



Taking water as an e+ample. @emember !irstly/ that water is considered to be a non$conductor o!

electricity. It can allow some electricity through it i! a high oltage is applied to it. This is due to the

presence o! a minute concentration o! L!i and 2L$ ions in the water. Loweer/ electrons cannot

!low through water.

&oalent substances do not conduct at all in solution.

Ionic substances are able to conduct electricity when they are dissoled in water.

The reason lies again in the !act that ionic substances are made o! charged particles $ ions.

*hen the ionic solid is dissoled in water the ionic lattice breaks up and the ions become !ree tomoe around in the water. *hen you pass electricity through the ionic solution/ the ions areable to carry the electric current because o! their ability to moe !reely. " solution conducts by meanso! !reely moing ions.

"n electrolyte is a liquid which can carry an electric current through it. Ionic solutions and ionicmelts are all electrolytes.

Electrolysis describes the process which takes place when an ionic solution or melt haselectricity passed through it.


44/926



#lasma is the state o! matter where some o! the electrons in a gas are stripped or 1ionied1

!rom their molecules or atoms. " plasma can be !ormed by high temperature/ or by application o!

a high electric or alternating magnetic !ield as noted aboe. Due to their lower mass/ the electrons

in a plasma accelerate more quickly in response to an electric !ield than the heaierpositie ions/

and hence carry the bulk o! the current.

acuum

It is a common belie! that electricity cannot !low through a acuum. This is howeer incorrect.

@emember that a conductor is 1something through which electricity can !low/1 rather than

1something which contains moable electricity.1 " acuum o!!ers no blockage to moingcharges. Should electrons be inected into a acuum/ the electrons will !low uninhibited and

unretarded. "s such/ a acuum is an ideal conductor.

This !act is taken adantage o! in many situations/ !rom teleisions to acuum ales. "

acuum arc can arise when the sur!aces o! metal electrodes in contact with a good acuum

%

%

r%

,

%

begin to emit electrons either through heating thermionic emission or ia an electric !ield that

is su!!icient to cause !ield emission. 2nce initiated/ a acuum arc can persist since the !reedparticles gain kinetic energy !rom the electric !ield/ heating the metal sur!aces through high

speed particle collisions. This process can create an incandescent cathode spot which !reesmore particles/ thereby sustaining the arc. "t su!!iciently high currents an incandescent anodespot may also be !ormed.

Electrical discharge in acuum is important !or certain types o! acuum tubes and !or higholtage acuum switches.

)$((

,se andAor disclosure isModule 3.) Static Electricity and &onduction

goerned by the statement TTS Integrated Training System


45/926

on page ) o! this &hapter. copyr g t


46/926



E

Intentionally 'lank

:

n

)$()Module 3.) Static Electricity and &onduction

TTS Integrated Training System ,se andAor disclosure isgoerned by the statement



47/926

$(

!,

i

( (%

% i



TTS Integrated

Training System

Module 3

%icence &ategory'(A')


3.3 Electrical Terminology


48/926


club66pro.co.uk question practice aid ,:

&opyright Gotice

&opyright. "ll worldwide rights resered. Go part o! this publication may be reproduced/

stored in a retrieal system or transmitted in any !orm by any other means whatsoeerH i.e.

photocopy/ electronic/ mechanical recording or otherwise without the prior written permission o!

Total Training Support %td.


.Fi

'asic knowledge !or categories "/ '( and ') are indicated by the allocation o! knowledge leels indicators (/ ) or

3 against each applicable subect. &ategory & applicants must meet either the category '( or the category ')basic knowledge leels.


8%EE% ( ". :

J " !amiliarisation with the principal elements o! the subect.2bectiesH


J The applicant should be able to gie a simple description o! the whole subect/ using common words and

e+amples. nJ The applicant should be able to use typical terms.

%EE% )J " general knowledge o! the theoretical and practical aspects o! the subect.

J "n ability to apply that knowledge.2bectiesH

J The applicant should be able to understand the theoretical !undamentals o! the subect.





%EE% 3

J" detailed knowledge o! the theoretical and practical aspects o! the subect.J " capacity to combine and apply the separate elements o! knowledge in a logical and comprehensiemanner.

2bectiesH

J The applicant should know the theory o! the subect and interrelationships with other subects.J The applicant should be able to gie a detailed description o! the subect using theoretical !undamentals


J The applicant should understand and be able to use mathematical !ormulae related to the subect.


J The applicant should be able to apply his knowledge in a practical manner using manu!acturer5s i:instructions.



3$)

Module 3.3 Electrical Terminology 3$(,se andAor disclosure is

goerned by the statementTTS Integrated Training System

on oaae ) o! this &hanter &onriaht )7(7


49/926

Mo u e 3.3 E ectr ca Term no ogyTTS Integrated Training System ,se andAor disclosure is

goerned by the statement &opyright )7(7 on page ) o! this &hapter


50/926

Integrated Training System,

Table o! &ontentsu

,Module 3.3 Electrical TerminologyElectrical Energy

Electrical &harges

Electric &urrent

Electrical @esistance

&onductance% Electrical %aws

i

% i

%I%I

Designed in association with the


=

=

6

B

(3

(3(;


51/926

Module 3.3 Electrical Terminology 3$3,se andAor disclosure is

goerned by the statement TTS Integrated Training Systemon page ) o! this &hapter &opyright )7(7


52/926



Module 3.3 Enabling 2becties

2bectie

Electrical TerminologyThe !ollowing terms/ their units and !actors a!!ecting themH

potential di!!erence/ electromotie !orce/ oltage/ current/

resistance/ conductance/ charge/ conentional current !low/

electron !low

3$;

E"S" 66 @e!erence %eel

3.3 )

T i

Module 3.3 Electrical TerminologyTTS Integrated Training System ,se andAor disclosure is



53/926



Module 3.3 Electrical Terminology

Electrical Energy

In the !ield o! physical science/ work must be de!ined as the product o! !orce and

displacement. That is/ the !orce applied to moe an obect and the distance the obect ismoed are the !actors o! work per!ormed.

,It is important to notice that no work is accomplished unless the !orce applied causes a change inthe position o! a stationary obect/ or a change in the elocity o! a moing obect. " worker

may tire by pushing against a heay wooden crate/ but unless the crate moes/ no work will be

accomplished.

, Energy

In our study o! energy and work/ we must de!ine energy as the ability to do work. In order toper!orm any kind o! work/ energy must be e+pended conerted !rom one !orm to another.

- , Energy supplies the required !orce/ or power/ wheneer any work is accomplished.2ne !orm o! energy is that which is contained by an obect in motion. *hen a hammer is set in

motion in the direction o! a nail/ it possesses energy o! motion. "s the hammer strikes the nail/

the energy o! motion is conerted into work as the nail is drien into the wood. The distance the

r(

El

((

L,

nail is drien into the wood depends on the elocity o! the hammer at the time it strikes the nail.

Energy contained by an obect due to its motion is called kinetic energy. "ssume that the

hammer is suspended by a string in a position one meter aboe a nail. "s a result o!graitational attraction/ the hammer will e+perience a !orce pulling it downward. I! the string is

suddenly cut/ the !orce o! graity will pull the hammer downward against the nail/ driing it into

the wood. *hile the hammer is suspended aboe the nail it has ability to do work because o! its

eleated position in the earth5s graitational !ield. Since energy is the ability to do work/ the

hammer contains energy.

Energy contained by an obect due to its position is called potential energy. The amount o!

potential energy aailable is equal to the product o! the !orce required to eleate the hammer

and the height to which it is eleated.

"nother e+ample o! potential energy is that contained in a tightly coiled spring. The amount o!energy released when the spring unwinds depends on the amount o! !orce required to wind the

spring initially.

3$=Module 3.3 Electrical Terminology


goerned by the tatement TTS Integrated Training System


54/926


ciub66pro.co.uk question practice aid

Electrical &harges

rom the preious study o! electrostatics/ you learned that a !ield o! !orce e+ists in the space

surrounding any electrical charge. The strength o! the !ield is directly dependent on the !orce o! the

charge.

The charge o! one electron might be used as a unit o! electrical charge/ since charges arecreated by displacement o! electronsK but the charge o! one electron is so small that it isimpractical to use.

The practical unit adopted !or measuring charges is the coulomb/ named a!ter the scientist&harles &oulomb. 2ne coulomb is equal to the charge o! 6/)B7/777/777/777/777/777 si+quintillion two hundred and eighty quadrillion or 6.)B + (7(B electrons.

*hen a charge o! one coulomb e+ists between two bodies/ one unit o! electrical potential

energy e+ists/ which is called the di!!erence o! potential between the two bodies. This is re!erred toas electromotie !orce/ or oltage/ and the unit o! measure is the olt.

(Electrical charges are created by the displacement o! electrons/ so that there e+ists an e+cesso! electrons at one point/ and a de!iciency at another point. &onsequently/ a charge must

always hae either a negatie or positie polarity. " body with an e+cess o! electrons is

considered to be negatie/ whereas a body with a de!iciency o! electrons is positie.

" di!!erence o! potential can e+ist between two points/ or bodies/ only i! they hae di!!erentcharges. In other words/ there is no di!!erence in potential between two bodies i! both hae ade!iciency o! electrons to the same degree. I!/ howeer/ one body is de!icient o! 6 coulombs

representing 6 olts/ and the other is de!icient by () coulombs representing () olts/ there is a

di!!erence o! potential o! 6 olts. The body with the greater de!iciency is positie with respect to theother.

In most electrical circuits only the di!!erence o! potential between two points is o! importance and

the absolute potentials o! the points are o! little concern. ery o!ten it is conenient to use onestandard re!erence !or all o! the arious potentials throughout a piece o! equipment. or thisreason/ the potentials at arious points in a circuit are generally measured with respect to the metalchassis on which all parts o! the circuit are mounted. The chassis is considered to be at eropotential and all other potentials are either positie or negatie with respect to the chassis. *henused as the re!erence point/ the chassis is said to be at ground potential.

2ccasionally/ rather large alues o! oltage may be encountered/ in which case the oltbecomes

too small a unit !or conenience. In a situation o! this nature/ the kiloolt k/ meaning (/777 olts/

is !requently used. "s an e+ample/ )7/777 olts would be written as )7 k. In other cases/ the olt

may be too large a unit/ as when dealing with ery small oltages. or thispurpose the millioltm/ meaning one$thousandth o! a olt/ and the microolt Y/ meaning one$millionth o! a olt/

are used. or e+ample/ 7.77( olt would be written as ( m/ and7.7777)= olt would be written as )= Y.

*hen a di!!erence in potential e+ists between two charged bodies that are connected by aconductor/ electrons will !low along the conductor. This !low is !rom the negatiely charged body to

the positiely charged body/ until the two charges are equalied and the potential di!!erence nolonger e+ists.

3$6

t. :

8

ni

F. (

8

8

Module 3.3 Electrical Terminology,se andlor disclosure is

TTS Integrated Training Systemgoerned by the statement

on page ) o! this chapters &opyright )7(7


55/926

opyr g on page ) o! this &hapter l E


56/926



%i

%

,

,

%I

,

"n analogy o! this action is shown in the two water tanks connected by a pipe and ale in

!igure 3.(. "t !irst the ale is closed and all the water is in tank ". Thus/ the water pressure

across the ale is at ma+imum. *hen the ale is opened/ the water !lows through the pipe

!rom " to ' until the water leel becomes the same in both tanks. The water then stops !lowing

in the pipe/ because there is no longer a di!!erence in water pressure between the two tanks.

T"G0 " T"G 0 '

&D

t

igure 3.( $ "n analogy o! potential di!!erence

Electron moement through an electric circuit is directly proportional to the di!!erence in potential

or electromotie !orce EM/ across the circuit/ ust as the !low o! water through thepipe in !igure3.( is directly proportional to the di!!erence in water leel in the two tanks.

" !undamental law o! electricity is that the electron !low is directly proportional to the appliedoltage. I! the oltage is increased/ the !low is increased. I! the oltage is decreased/ the !low isdecreased.

Module 3.3 Electrical Terminology 3$8,se andAor disclosure is

goerned by the statement TTS Integrated Training System


57/926

on page ) o! this &hapter opyr g t


58/926


ciub6dpro.co.uk question practice aid

Electric &urrent

Electron !low

It has been proen that electrons negatie charges moe through a conductor in response to anelectric !ield. Electron current !low will be used throughout this e+planation. Electroncurrent is de!ined as the directed !low o! electrons. The direction o! electron moement is !rom a

region o! negatie potential to a region o! positie potential. There!ore electron !low can be said to!low !rom negatie to positie. The direction o! current !low in a material is determined by the

polarity o! the applied oltage.

&onentional &urrent low

In the ,0 and Europe/ conentional current !low is said to be !rom positie to negatie potential $the opposite way to the actual !low o! electrons.

&onentional current was de!ined early in thehistory o! electrical science as a !low o! positie

charge. In solid metals/ like wires/ the positie low o! positie charge

charge carriers are immobile/ and only the %..:negatiely charged electrons !low. 'ecause the

electron carries negatie charge/ the electron

current is in the direction opposite to that o!

conentional or electric current.

Electric charge moes !rom the positie side o!

the power source to the negatie.

In other conductie materials/ the electric current igure 3.) $ &onentional current

is due to the !low o! charged particles in both !low directiondirections at the same time. Electric currents in

electrolytes are !lows o! electrically charged atoms ions/ which e+ist in both positie and

negatie arieties. or e+ample/ an electrochemical cell may be constructed with salt water a

solution o! sodium chloride on one side o! a membrane and pure water on the other. Themembrane lets the positie sodium ions pass/ but not the negatie chloride ions/ so a net

current results. Electric currents in plasma are !lows o! electrons as well as positie andnegatie ions. In ice and in certain solid electrolytes/ !lowing protons constitute the electric

current. To simpli!y this situation/ the original de!inition o! conentional current still stands.n

There are also materials where the electric current is due to the !low o! electrons and yet it isconceptually easier to think o! the current as due to the !low o! positie 1holes1 the spots that

should hae an electron to make the conductor neutral. This is the case in a p$type

semiconductor. %.K

These E"S" #art$66 Module 3 notes will use conentional current notation throughout/ unlessotherwise stated/ and then only !or speci!ic reasons.

r$/

3$B Module 3.3 Electrical TerminologyTTS Integrated Training System ,se and!or disclosure is

goerned by the statement

&opyright )7(7 gon page ) o! this &hapter


59/926



@andom Dri!t

"ll materials are composed o! atoms/ each o! which is capable o! being ionised. I! some !orm o!

energy/ such as heat/ is applied to a material/ some electrons acquire su!!icient energy to moe to

a higher energy leel. "s a result/ some electrons are !reed !rom their parent atom5s which

then becomes ions. 2ther !orms o! energy/ particularly light or an electric !ield/ will cause

ionisation to occur.

The number o! !ree electrons resulting !rom ionisation is dependent upon the quantity o! energy

applied to a material/ as well as the atomic structure o! the material. "t room temperature somematerials/ classi!ied as conductors/ hae an abundance o! !ree electrons. ,nder a similar

%i

,

LR

,

%

condition/ materials classi!ied as insulators hae relatiely !ew !ree electrons.

In a study o! electric current/ conductors are o! maor concern. &onductors are made up o!

atoms that contain loosely bound electrons in their outer orbits. Due to the e!!ects o! increased

energy/ these outermost electrons !requently break away !rom their atoms and !reely dri!tthroughout the material. The !ree electrons/ also called mobile electrons/ take a path that is not

predictable and dri!t about the material in a haphaard manner. &onsequently such a moement istermed random dri!t.

It is important to emphasie that the random dri!t o! electrons occurs in all materials. The degree o!

random dri!t is greater in a conductor than in an insulator.

Directed Dri!t

"ssociated with eery charged body there is an electrostatic !ield. 'odies that are charged alike

repel one another and bodies with unlike charges attract each other. "n electron will be a!!ected by

an electrostatic !ield in e+actly the same manner as any negatiely charged body. It isrepelled by a negatie charge and attracted by a positie charge. I! a conductor has a di!!erence in

potential impressed across it/ as shown in !igure 3.3/ a direction is imparted to the random dri!t.This causes the mobile electrons to be repelled away !rom the negatie terminal andattracted toward the positie terminal. This constitutes a general migration o! electrons !rom one

end o! the conductor to the other. The directed migration o! mobile electrons due to the potential

di!!erence is called directed dri!t.

Module 3.3 Electrical Terminology 3$Cgoerned by the statement TTS Integrated Training Systemon page ) 7( this &hapter &opyright )7(7

$$$



60/926



r1

igure 3.3 $ Directed dri!t

The directed moement o! the electrons occurs at a relatiely low elocity rate o! motion in aparticular direction. The e!!ect o! this directed moement/ howeer/ is !elt almost

instantaneously/ as e+plained by the use o! !igure 3.3. "s a di!!erence in potential is impressedacross the conductor/ the positie terminal o! the battery attracts electrons !rom point ". #oint "

now has a de!iciency o! electrons. "s a result/ electrons are attracted !rom point ' to point ".

#oint ' has now deeloped an electron de!iciency/ there!ore/ it will attract electrons. This samee!!ect occurs throughout the conductor and repeats itsel! !rom points D to &. "t the same instant

the positie battery terminal attracted electrons !rom point "/ the negatie terminal repelled

electrons toward point D. These electrons are attracted to point D as it gies up electrons topoint &. This process is continuous !or as long as a di!!erence o! potential e+ists across theconductor. Though an indiidual electron moes quite slowly through the conductor/ the e!!ect o!

a directed dri!t occurs almost instantaneously. "s an electron moes into the conductor at pointD/ an electron is leaing at point ". This action takes place at appro+imately the speed a light

(B6/777 Miles #er Second.

3$(7

. .

Module 3.3 Electrical Terminology,se andAor disclosure is

TTS Integrated Training System goerned by the statement &opyright )7(7 gon page ) o! this &hapter T


61/926

Integrated Training System,

%i

%

I

%i

%

Magnitude o! &urrent low

igure 3.; $ E!!ect o! directed dri!t.

Designed in association with theclub66pro.co.uk question practice aid

Electric current has been de!ined as the directed moement o! electrons. Directed dri!t/

there!ore/ is current and the terms can be used interchangeably. The e+pression directed dri!t isparticularly help!ul in di!!erentiating between the random and directed motion o! electrons.Loweer/ current !low is the terminology most commonly used in indicating a directed

moement o! electrons.

$%9

%

The magnitude o! current !low is directly related to the amount o! energy that passes through a

conductor as a result o! the dri!t action. "n increase in the number o! energy carriers the mobile

electrons or an increase in the energy o! the e+isting mobile electrons would proide an increase incurrent !low. *hen an electric potential is impressed across a conductor/ there is an increase in the

elocity o! the mobile electrons causing an increase in the energy o! the carriers. There is also thegeneration o! an increased number o! electrons proiding added carriers o! energy. The additional

number o! !ree electrons is relatiely small/ hence the magnitude o! current !low is primarily

dependent on the elocity o! the e+isting mobile electrons.

The magnitude o! current !low is a!!ected by the di!!erence o! potential in the !ollowing manner.

Initially/ mobile electrons are gien additional energy because o! the repelling and attracting

electrostatic !ield. I! the potential di!!erence is increased/ the electric !ield will be stronger/ the

amount o! energy imparted to a mobile electron will be greater/ and the current will be

increased. I! the potential di!!erence is decreased/ the strength o! the !ield is reduced/ the

%energy supplied to the electron is diminished/ and the current is decreased.Measurement o! &urrentThe magnitude o! current is measured in amperes. " current o! one ampere is said to !low

Lwhen one coulomb o! char *e passes a point in one second. @emember/ one coulomb is equalto the charge o! 6.)B + (7( electrons.

Module 3.3 Electrical Terminology 3$((,se andAor disclosure is


62/926

goerned by the statement TTS Integrated Training Systemon page ) o! this &hapter &opyright )7(7


63/926


club66pro.co.uk question practice aid lF (

requently/ the ampere is much too large a unit !or measuring current. There!ore/ the

milliampere m"/ one$thousandth o! an ampere/ or the microampere Y"/ one$millionth o! anampere/ is used. The deice used to measure current is called an ammeter and will bediscussed in detail in a later module.

" current o! ( "mp is !lowing when a quantity o! ( &oulomb o! charge !lows !or ( second.

The current I in amperes can be calculated with the !ollowing equationH

n

*hereH

n

is the electric charge in coulombs ampere seconds

t is the time in seconds

It !ollows thatH

tR.$t

3$()

and

r

:

Module 3.3 Electrical TerminologyTTS Integrated Training System ,se andAor disclosure is



64/926


65/926

ectrical @esistance


66/926

tegrated Training SystemDesigned in association with the


%i (,

!I,1

,(% i

It is known that the directed moement o! electrons constitutes a current !low. It is also knownthat the electrons do not moe !reely through a conductor5s crystalline structure. Some materials

o!!er little opposition to current !low/ while others greatly oppose current !low. This opposition to

current !low is known as resistance @/ and the unit o! measure is the ohm. The standard o!measure !or one ohm is the resistance proided at ero degrees &elsius by a column o!mercury haing a cross$sectional area o! one square millimetre and a length o! (76.3centimetres." conductor has one ohm o! resistance when an applied potential o! one olt produces a

current o! one ampere. The symbol used to represent the ohm is the


67/926

Integrated Training SystemDesigned in association with theclub66pro.co.uk question practice aid

Electrical %aws

araday5s %aw

araday5s law o! induction states that the induced electromotie !orce in a closed loop o! wire isdirectly proportional to the time rate o! change o! magnetic !lu+ through the loop.

2hm5s %aw"n electrical circuit/ the current passing through a conductor between two points is directly

proportional to the potential di!!erence i.e. oltage drop or oltage across the two points/ and

inersely proportional to the resistance between them.

0irchho!!5s %aws

#urrent Law $"t any point in an electrical circuit where charge density is not changing in

time/ the sum o! currents !lowing towards that point is equal to the sum o! currents!lowing away !rom that point.

%oltage Law$ The directed sum o! the electrical potential di!!erences around any closedcircuit must be ero.

%ens5s %aw

The induced current in a loop is in the direction that creates a magnetic !ield that opposes thechange in magnetic !lu+ through the area enclosed by the loop. That is/ the induced currenttends to keep the original magnetic !lu+ through the !ield !rom changing.

3$(;

:

L. J

Module 3.3 Electrical TerminologyITS Integrated Training System ,se andAor disclosure is


E l


68/926



TTS Integrated

Training System

Module 3

% i,

%

%icence &ategory '(A6)


3.;


69/926


ciub66pro.co.uk question practice aid

&opyright Gotice

Z &opyright. "ll worldwide rights resered. Go part o! this publication may be reproduced/ i r %


photocopy/ electronic/ mechanical recording or otherwise without the prior written permission o!Total Training Support %td.


'asic knowledge !or categories "/ '( and ') are indicated by the allocation o! knowledge leels indicators (/ ) or

3 against each applicable subect. &ategory & applicants must meet either the category '( or the category ')basic knowledge leels.The knowledge leel indicators are de!ined as !ollowsH


2bectiesH


J The applicant should be able to gie a simple description o! the whole subect/ using common words ande+amples.


%EE% )J " general knowledge o! the theoretical and practical aspects o! the subect.J "n ability to apply that knowledge.

2bectiesHJ The applicant should be able to understand the theoretical !undamentals o! the subect. n





%EE% 3 nJ " detailed knowledge o! the theoretical and practical aspects o! the subect.J " capacity to combine and apply the separate elements o! knowledge in a logical and comprehensie

manner.2bectiesH


J The applicant should be able to gie a detailed description o! the subect using theoretical !undamentalsand speci!ic e+amples.

J The applicant should understand and be able to use mathematical !ormulae related to the subect.J The applicant should be able to read/ understand and prepare sketches/ simple drawings and schematics

describing the subect.




;$) Module 3.;


70/926



%

%

$8

%

L

%

T

%

Table o! &ontents

Module 3.;


71/926

L on pace ) o! this &hapter. opyr g


72/926


club


73/926



% Module 3.;


74/926



oltage #roduced by riction

The !irst method discoered !or creating a oltage was that o! generation by !riction. The

deelopment o! charges by rubbing a rod with !ur is a prime e+ample o! the way in which a

oltage is generated by !riction. 'ecause o! the nature o! the materials with which this oltage isgenerated/ it cannot be coneniently used or maintained. or this reason/ ery little practical use hasbeen !ound !or oltages generated by this method.

In the search !or methods to produce a oltage o! a larger amplitude and o! a more practicalnature/ machines were deeloped in which charges were trans!erred !rom one terminal to

another by means o! rotating glass discs or moing belts. The most notable o! these machines isthe an de


75/926

&opyright )7(7 page ) o! this &hapter..


76/926


&lub66pro.co.uk question practice aid

&rystals o! this type also possess another interesting property/ the 1conerse pieoelectric

e!!ect.1 That is/ they hae the ability to conert electrical energy into mechanical energy. "

oltage impressed across the proper sur!aces o! the crystal will cause it to e+pand or contract8(

% i

r

,

,

its sur!aces in response to the oltage applied.

oltage #roduced by Leat

*hen a length o! metal/ such as copper/ is heated at one end/ electrons tend to moe away !romthe hot end toward the cooler end. This is true o! most metals. Loweer/ in some metals/ such asiron/ the opposite takes place and electrons tend to moe toward the hot end. Thesecharacteristics are illustrated in !igure ;.). The negatie charges electrons are moing through thecopper away !rom the heat and through the iron toward the heat. They cross !rom the iron to thecopper through the current meter to the iron at the cold unction. This deice is generally re!erred toas a thermocouple

&2%D

:,II&lloG

igure ;.) $ oltage produced by heat.

Thermocouples hae somewhat greater power capacities than crystals/ but their capacity is still

ery small i! compared to some other sources. The thermoelectric oltage in a thermocouple

depends mainly on the di!!erence in temperature between the hot and cold unctions.&onsequently/ they are widely used to measure temperature/ and as heat$sensing deices inautomatic temperature control equipment. Thermocouples generally can be subected to much

greater temperatures than ordinary thermometers/ such as the mercury or alcohol types.

oltage #roduced by %ight

*hen light strikes the sur!ace o! a substance/ it may dislodge electrons !rom their orbits around thesur!ace atoms o! the substance. This occurs because light has energy/ the same as any moing!orce.

Some substances/ mostly metallic ones/ are !ar more sensitie to light than others. That is/

more electrons will be dislodged and emitted !rom the sur!ace o! a highly sensitie metal/ with a

gien amount o! light/ than will be emitted !rom a less sensitie substance. ,pon losing

electrons/ the photosensitie light$sensitie metal becomes positiely charged/ and an electric!orce is created. oltage produced in this manner is re!erred to as a photoelectric oltage.

Module 3.;


77/926



The photosensitie materials most commonly used to produce a photoelectric oltage are

arious compounds o! siler o+ide or copper o+ide. " complete deice which operates on the

photoelectric principle is re!erred to as a 1photoelectric cell.1 There are many di!!erent sies and

types o! photoelectric cells in use/ and each seres the special purpose !or which it is designed.

Gearly all/ howeer/ hae some o! the basic !eatures o! the photoelectric cells shown in !igure;.3.

#L2T2SEGSITIE SI%E@2UIDE S,@"&E

H .%I/.

%I


78/926



The power capacity o! a photocell is ery small. Loweer/ it reacts to light$intensity ariations in an

e+tremely short time. This characteristic makes the photocell ery use!ul in detecting or

accurately controlling a great number o! operations. or instance/ the photoelectric cell/ or some

!orm o! the photoelectric principle/ is used in teleision cameras/ automatic manu!acturingprocess controls/ door openers/ burglar alarms/ and so !orth.

i

..

F

I,

r9

I

,

oltage #roduced by &hemical "ction

oltage may be produced chemically when certain substances are e+posed to chemical action. I!

two dissimilar substances usually metals or metallic materials are immersed in a solution that

produces a greater chemical action on one substance than on the other/ a di!!erence o!

potential will e+ist between the two. I! a conductor is then connected between them/ electrons

will !low through the conductor to equalie the charge. This arrangement is called a primary cell.

The two metallic pieces are called electrodes and the solution is called the electrolyte. Theoltaic cell illustrated in !igure ;.; is a simple e+ample o! a primary cell. The di!!erence o!potential results !rom the !act that material !rom one or both o! the electrodes goes into solution in

the electrolyte/ and in the process/ ions !orm in the icinity o! the electrodes. Due to the electric!ield associated with the charged ions/ the electrodes acquire charges.

VIG& &2##E@

E%E&T@2DE . . E%E&T@2DE

igure ;.; $ oltaic cell.

The amount o! di!!erence in potential between the electrodes depends principally on the metals

used. The type o! electrolyte and the sie o! the cell hae little or no e!!ect on the potential

di!!erence produced.

There are two types o! primary cells/ the wet cell and the dry cell. In a wet cell the electrolyte is

a liquid. " cell with a liquid electrolyte must remain in an upright position and is not readily

transportable. "n automotie battery is an e+ample o! this type o! cell. The dry cell/ much more

commonly used than the wet cell/ is not actually dry/ but contains an electrolyte mi+ed withother materials to !orm a paste. Torches and portable radios are commonly powered by dry

cells.

Module 3.;


79/926



'atteries are !ormed when seeral cells are connected together to increase electrical output.

oltage #roduced by Magnetism

Magnets or magnetic deices are used !or thousands o! di!!erent obs. 2ne o! the most use!ul andwidely employed applications o! magnets is in the production o! ast quantities o! electric power

!rom mechanical sources. The mechanical power may be proided by a number o!di!!erent sources/ such as gasoline or diesel engines/ and water or steam turbines. Loweer/ the

!inal conersion o! these source energies to electricity is done by generators employing theprinciple o! electromagnetic induction. These generators/ o! many types and sies/ are

discussed in other modules in this series. The important subect to be discussed here is the!undamental operating principle o! all such electromagnetic$induction generators.

To begin with/ there are three !undamental conditions which must e+ist be!ore a oltage can be n

produced by magnetism. K (

J There must be a conductor in which the oltage will be produced.

J There must be a magnetic !ield in the conductor5s icinity.

J There must be relatie motion between the !ield and conductor. The conductor must bemoed so as to cut across the magnetic lines o! !orce/ or the !ield must be moed so that nthe lines o! !orce are cut by the conductor.

In accordance with these conditions/ when a conductor or conductors moe across a magnetic!ield so as to cut the lines o! !orce/ electrons within the conductor are propelled in onedirection or another. Thus/ an electric !orce/ or oltage/ is created.

In !igure ;.=/ note the presence o! the three conditions needed !or creating an induced oltage.

;$(7Module 3.;


80/926



"

&

direction o!

motion reersed

igure ;.= $ oltage produced by magnetism.

J " magnetic !ield e+ists between the poles o! the &$shaped magnet.

J There is a conductor copper wire.

J There is a relatie motion. The wire is moed back and !orth across the magnetic !ield.

J In !igure ;.= iew "/ the conductor is moing toward the !ront o! the page and the

electrons moe !rom le!t to right.

The moement o! the electrons occurs because o! the magnetically induced EM acting on theelectrons in the copper. The right$hand end becomes negatie/ and the le!t$hand end positie. Theconductor is stopped at iew '/ motion is eliminated one o! the three required conditions/ and

there is no longer an induced EM. &onsequently/ there is no longer any di!!erence in

potential between the two ends o! the wire. The conductor at iew & is moing away !rom the !ronto! the page. "n induced EM is again created. Loweer/ note care!ully that the reersal o! motionhas caused a reersal o! direction in the induced EM.

I! a path !or electron !low is proided between the ends o! the conductor/ electrons will leae the

negatie end and !low to the positie end. This condition is shown in part iew D. Electron !lowwill continue as long as the EM e+ists. In studying !igure ;.=/it should be noted that the

induced EM could also hae been created by holding the conductor stationary and moing the

magnetic !ield back and !orth.

The more comple+ aspects o! power generation by use o! mechanical motion and magnetism are

discussed later in &hapter (; $ D& MotorA


81/926



r/ 9%

intentionally 'lank

I

;$()Module 3.;


82/926



([

TTS Integrated

Training System,

Module 3

, %icence &ategory'(A')


3.= D& Sources o! Electricity

Module 3.= D& Sources o! Electricity =$(


83/926



&opyright Gotice

&opyright. "ll worldwide rights resered. Go part o! this publication may be reproduced/


photocopy/ electronic/ mechanical recording or otherwise without the prior written permission o!Total Training Support %td.

0nowledge %eels $$$ &ategory "/ '(/ ') and & "ircra!t Maintenance%icence



! l


2bectiesH


e+amples.


%EE% )J " general knowledge o! the theoretical and practical aspects o! the subect.

J "n ability to apply that knowledge.

2bectiesHJ The applicant should be able to understand the theoretical !undamentals o! the subect.

Je+amples.

subect.

subect.


%EE% 3J " detailed knowledge o! the theoretical and practical aspects o! the subect.

Jmanner.

2bectiesH



J

Jdescribing the subect

Date post:	02-Jun-2018
Category:	Documents
Upload:	indirfan-haerudin
View:	217 times
Download:	0 times

3. Electrical Fundamental

Documents