TVET FIRST
Electronics
Electronics
NQF Level 2
Electronics
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NQF Level 2
NQF Level 2
Student’s Book
Electronics 2 s.indd 1
RBJ van Heerden & Jowaheer Consulting and Technologies
STUDENT’S BOOK
TVET FIRST
2015/02/25 8:47 AM
Electronics
NQF Level 2
Student’s Book
RBJ van Heerden & Jowaheer Consulting and Technologies
Electronics NQF Level 2
Student’s Book
© RBJ van Heerden & Jowaheer Consulting and Technologies, 2006
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First published in 2006 by
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Distributed by Macmillan South Africa [Pty] Ltd
ISBN: 978-1-9200-7512-5
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Contents
Topic 1 Fundamentals of electricity .................................................................... 1
Module 1 Electron theory ........................................................................................................ 2
Unit 1.1: Atomic theory in terms of electrical materials .............................................................. 3
Unit 1.2: Electron flow in a conductor ............................................................................................ 5
Unit 1.3: Basic electric circuits ...................................................................................................... 8
Module 2 Magnetic theory ....................................................................................................... 11
Unit 2.1: Permanent magnets ........................................................................................................ 12
Unit 2.2: Characteristics of magnetic lines of flux ........................................................................ 14
Unit 2.3: Electromagnetism............................................................................................................ 16
Unit 2.4: Magnetic field and current flow in terms of movement ................................................. 19
Module 3 Fundamentals of power generation and distribution ............................................... 22
Unit 3.1: Electricity production ....................................................................................................... 23
Unit 3.2: Conversion of resources .................................................................................................. 27
Unit 3.3: Direct current (d.c.) generator ........................................................................................ 33
Unit 3.4: Alternating current (a.c.) generator ................................................................................ 35
Module 4 Electrical units and symbols .................................................................................... 38
Unit 4.1: Electrical units and symbols ........................................................................................... 39
Unit 4.2: Voltage, current and resistance....................................................................................... 43
Unit 4.3: Resistance ........................................................................................................................ 45
Unit 4.4: Power consumed in a d.c. circuit .................................................................................... 47
Module 5 D.c. resistive circuits and calculations ..................................................................... 48
Unit 5.1: Draw and interpret circuits.............................................................................................. 49
Unit 5.2: Calculations of resistive circuits ..................................................................................... 54
Topic 2 Basic electronic theory and concepts ..................................................... 59
Module 6 Atomic and electron theory ...................................................................................... 60
Unit 6.1: Structure of the atom ...................................................................................................... 61
Unit 6.2: Valency electrons ............................................................................................................. 64
Unit 6.3: Conduction with different types of materials .................................................................. 66
Unit 6.4: Bonding processes between different molecule types ................................................... 68
Unit 6.5: Doping of intrinsic materials ........................................................................................... 71
Module 7 Operation of basic electronic components ............................................................... 75
Unit 7.1: Resistor types and values ................................................................................................ 76
Unit 7.2: Capacitor types and values .............................................................................................. 84
Unit 7.3: Inductor types and values ................................................................................................ 92
Contents
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Unit 7.4: Effect of resistance, capacitance and inductance on a circuit........................................ 95
Module 8 Operation of a P-N diode .......................................................................................... 99
Unit 8.1: Creation and biasing of a P-N junction ........................................................................... 100
Unit 8.2: Forward and reverse biasing ........................................................................................... 104
Unit 8.3: Types of specialised diodes ............................................................................................. 107
Unit 8.4: Basic calculations relating to semiconductor theory ..................................................... 110
Module 9 Power supplies.........................................................................................................113
Unit 9.1: Transformers ................................................................................................................... 114
Unit 9.2: Rectifier techniques ......................................................................................................... 117
Unit 9.3: Half-wave and full-wave rectifiers ..................................................................................122
Topic 3 Electrical safety standards ..................................................................... 129
Module 10 The nature of electrical safety ...............................................................................130
Unit 10.1: The dangers of electricity .............................................................................................. 131
Unit 10.2: Earthing and safety practices ........................................................................................ 133
Unit 10.3: Apparatus isolation ........................................................................................................ 135
Module 11 Governance of electrical safety ..............................................................................138
Unit 11.1: Statutory requirements related to electrical safety ...................................................... 139
Module 12 First aid related to electrical incidents ..................................................................142
Unit 12.1: Electrical shock.............................................................................................................. 143
Topic 4 Use and care of hand-held electrical test instruments .......................... 147
Module 13 Principles related to hand-held electrical test instruments ..................................148
Unit 13.1: Hand-held electrical test instruments .......................................................................... 149
Unit 13.2: Basic measurements explained by means of Ohm’s law ............................................. 152
Module 14 Care for hand-held electrical instruments.............................................................155
Unit 14.1: Personal protective equipment .....................................................................................156
Unit 14.2: Care, maintenance and storage of test instruments .................................................... 159
Module 15 Using hand-held electrical test instruments..........................................................162
Unit 15.1: Practical considerations when working with PPEs and hand-held test
instruments .................................................................................................................... 163
Topic 5 Soldering and de-soldering techniques .................................................167
Module 16 Planning of the work task ......................................................................................168
Unit 16.1: Identify and select appropriate hand tools....................................................................169
Unit 16.2: Safe use of hand tools related to the job ......................................................................173
iv
Contents
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Module 17 Prepare for soldering .............................................................................................176
Unit 17.1: Getting ready for a soldering task .................................................................................177
Module 18 Performing soldering/de-soldering tasks .............................................................180
Unit 18.1: Preparing for a soldering task ......................................................................................181
Unit 18.2: Soldering connections ...................................................................................................184
Module 19 Inspection of soldering joints .................................................................................189
Unit 19.1: Recognising a good solder joint ....................................................................................190
Unit 19.2: Reasons for poorly soldered joints................................................................................194
Module 20 Completing the work task ......................................................................................197
Unit 20.1: Cleaning the work area ..................................................................................................198
Unit 20.2: Disposing of waste material ..........................................................................................201
Topic 6 Construct basic electronic circuits .........................................................203
Module 21 Plan to construct basic electronic circuits .............................................................204
Unit 21.1: Interpret instructions and planning ..............................................................................205
Unit 21.2: Identify tools and components ......................................................................................207
Module 22 Construct basic electronic circuits .........................................................................210
Unit 22.1: Analysing circuit diagrams to ensure correct component layout .................................211
Unit 22.2: Soldering the components.............................................................................................215
Module 23 Test and commission circuits .................................................................................216
Unit 23.1: Checking the circuit visually for faults ..........................................................................217
Unit 23.2: Connecting the circuit according to operating procedures ..........................................218
Module 24 Complete the work task .........................................................................................220
Unit 24.1: Good housekeeping ........................................................................................................221
Topic 7 Principles of digital logic ........................................................................223
Module 25 The binary number system ....................................................................................224
Unit 25.1: The difference between analogue and digital ...............................................................225
Unit 25.2: The decimal system .......................................................................................................226
Unit 25.3: The binary number system ............................................................................................228
Module 26 Basic logic gates.....................................................................................................238
Unit 26.1: Logic gates .....................................................................................................................239
Topic 8 Basic programmable logic controllers ...................................................247
Module 27 Input / output peripherals ......................................................................................248
Unit 27.1: PLC internal architecture, input and output devices ....................................................249
Contents
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Unit 27.2: Work site hazards and precautions ...............................................................................253
Module 28 Field devices interfaced to a PLC ...........................................................................255
Unit 28.1: Input / output devices interfaced to a PLC ....................................................................256
Unit 28.2: Personal safety equipment ............................................................................................258
Module 29 The processor in a programmable logic controller ................................................259
Unit 29.1: Function of the processor ..............................................................................................260
Unit 29.2: Changing the battery on a PLC and the function of indicator lights ............................262
Module 30 The back plane and power supply of a PLC ............................................................265
Unit 30.1: Back plane .....................................................................................................................266
Unit 30.2: Power supply ..................................................................................................................268
Module 31 The programming terminal ....................................................................................270
Unit 31.1: Programming device ......................................................................................................271
Unit 31.2: Ladder diagrams ............................................................................................................272
Topic 9 Basic concepts of telecommunications ..................................................275
Module 32 Concepts used in telecommunications ...................................................................276
Unit 32.1: Basic concepts ...............................................................................................................277
Module 33 The telephone and fax machine..............................................................................279
Unit 33.1: The telephone ................................................................................................................280
Unit 33.2: Facsimile ........................................................................................................................282
Module 34 Underlying technologies used in telecommunications ...........................................284
Unit 34.1: Modulation and multiplexing .........................................................................................285
Unit 34.2: Concepts of impedance, termination, reflection, cross-talk, noise and signal level ...290
Unit 34.3: Transmission media .......................................................................................................292
Unit 34.4: Analogue and digital transmission ................................................................................295
Unit 34.5: Operation of a data network ..........................................................................................297
Module 35 Networks and systems in telecommunication ........................................................301
Unit 35.1: Public switched telecommunication network (PSTN) ...................................................302
Unit 35.2: Data network services ...................................................................................................303
Unit 35.3: Computer networks .......................................................................................................306
Glossary...................................................................................................................................307
Abbreviations used in this book ...............................................................................................313
Index ........................................................................................................................................315
vi
Contents
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Topic 1
Fundamentals of
electricity
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Module 1
Electron theory
Overview
Electricity is an invisible force that can produce heat, light and motion
by repulsion, or attraction. Many other physical effects are also
possible. In this module you will learn about electric charges, current,
voltage and resistance. You will become familiar with the following
electrical units: the coulomb for measuring charge, the ampere for
measuring current, the volt for measuring potential difference and
the ohm for measuring the resistance of a conductor. Finally, you will
apply this knowledge to electrical circuits.
When you have completed this module, you should be able to:
⦁ explain atomic theory in terms of electrical materials
⦁ explain electron flow in a conductor with reference to electron
theory
⦁ explain the effect of an external power source on the electrons in a
conductor with reference to electron theory
⦁ explain the principles of basic electrical circuits in terms of a power
source and load
⦁ explain the basic principles of voltage and current flow in an
electrical circuit in terms of electron theory.
2
Topic 1, Module 1
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Unit 1.1:Atomic theory in terms of
electrical materials
The structure of the atom
We can see the effects and uses of electricity all around us batteries,
static charge, street lights, stoves and refrigerators, lightning, radio and
television, cell phones and many more. All these different ‘forms of
electricity’ have something in common. They are all basic particles of
electric charge with opposite polarities. Everything we can see, feel or
touch is called matter and matter is made up of atoms. The atom is the
smallest part of an element that can exist and still retain the properties
of the element.
An atom consists of three kinds of particles, namely electrons, protons
and neutrons. The centre part of an atom is called the nucleus and it
consists of protons and neutrons. Protons have a positive electrical
charge whereas neutrons are electrically neutral (they have no electric
charge). Electrons are particles with a negative charge that move
around the nucleus. Fig. 1.1 shows the structure of the atom.
Note
Y
ou will learn more about the atom and
electron theory in Module 6.
proton
neutron
electron
P N
Fig. 1.1 The structure of an
atom
Electric charge
All materials, including solids, liquids and gases, contain two basic
particles of electric charge: the electron and the proton. The electron is
the smallest amount of electrical charge and has a characteristic called
negative polarity. The proton is the basic particle with a positive polarity.
Words &Terms
The electrical characteristics of a substance depend on the arrangement
of the electrons and protons as the building blocks of the substance.
This applies to any object you can see around you. Take for instance
your pen or pencil. It consists of matter and therefore it is made up of
atoms. It therefore has electrons and protons, but there is no sign of
any electricity in or around your pen! Why is that?
Electric charge:a property of
matter that causes particles to
attract or repel one another
The reason is that the number of electrons equals the number of
protons, and therefore the opposite electrical forces cancel each other
out, making the pen electrically neutral. This means that the opposing
forces are exactly balanced.
Matter:anything that occupies
space and has mass
If we want to separate the protons and electrons in a substance, then
work must be done. Changing the balance of forces will produce
evidence of electricity. A battery, which is the simplest form of an
electrical supply that we all know, can do electrical work. The chemical
energy in the container of the battery separates the electrical charges to
produce an excess of electrons at the one terminal (called the negative
pole) and an excess of protons at the other terminal (called the positive
pole).
Element:a substance made of
only one type of atom and that
cannot be broken down into
simpler substances
These two opposite charges at the two terminals can supply electrical
energy to a device by means of a transport system known as conductors
of electricity. This combination of a battery, conductors and a device (for
example, a light bulb), is called an electrical circuit.
Fig. 1.2 shows simple 1,5 V battery cells. Note the positive () and ()
terminals of the cell. It also shows the circuit symbol for a cell.
Polarity:the positive or negative
direction of the charge that flows
in a conductor
Atoms:the tiny particles from
which elements are made
Energy:the ability to do work;
electric energy is the result of
power developed over a certain
period of time
Circuit:the path along which
electricity flows
Electricity:a kind of energy that
we use to power electric
appliances such as stoves, radios
and computers
Unit 1.1: Atomic theory in terms of electrical materials
01375 topic_01.indd 3
3
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Think about it
D
cell
C
cell
AAA cell
AA cell
No 6
cell
It is wrong to call a single cell, as
shown in Fig. 1.2, a battery. In
Electronics, the term ‘ battery’ is
only used when two or more
cells are connected in series or
in parallel in a circuit.
PP3
battery
Fig. 1.2 A cell
Assessment activity 1.1
1.
Briefly describe what you understand by the term electricity.
2.
List five applications of electricity.
3.
What do you understand by the term ‘component’?
4.
Name the two electrical charges.
5.
Name the two main substances which are important to us in
electricity and state their charges.
6.
What is the charge of this book in front of you? Why?
7.
Name the simplest source of electrical energy.
8.
Define an electrical circuit.
9.
Draw the circuit symbol of the cell.
10. Name two types of batteries (not cells) in use today.
4
Topic 1, Module 1
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Unit 1.2:Electron flow in a conductor
Electrons and protons can be grouped in different ways, but all of them
strive towards a specific combination called a stable arrangement.
Each stable combination of electrons and protons makes one particular
type of unit, namely an atom. The simplest atom we get is a gas named
hydrogen. Fig. 1.1 shows a hydrogen atom.
The atom consists of a central mass called the nucleus and electrons
that move in concentric circles around the nucleus. Protons are part
of the nucleus. In their natural state, electrons are in constant motion
around the nuclei of the atom, as shown in Fig. 1.1. This motion is the
basis of electrostatic and magnetic energy. (You will learn more about
the nature of the atom and the movement of electrons in Module 6.)
A proton is 1 840 times heavier than a single electron, but remember,
the proton has a positive charge and the electron a negative charge,
so the charges cancel each other out. The electrical charges are of the
same value but opposite in spite of the mass difference between them.
Terms
&
s
d
r
Wo
ged
y chan
asil
:not e
s
Stable
:circle
circles entre at
ic
r
t
n
Conce have their c
ll
that a e point
m
a
s
the
Think about it
The flow of electrons in a conductor
To transmit electrical energy or convert it into other forms of energy,
there must be a continuous flow of electrons through the conductors
and components of a circuit.
Our planet consists of matter. Matter exists in three forms: liquid, solid
and gas. We are only interested in the solid state of matter because
normal conductors in an electrical circuit are made out of copper (or
aluminium). Copper is an excellent conductor of electricity because it
has a large number of valence electrons (see Module 6) that can pass
through the material quite easily under the influence of a driving force.
This causes some of the electrons in the conductor to become free.
When a driving force (such as the cell in Fig. 1.2) is applied to the ends
of a copper conductor, differences in potential exist between all points
along the conductor. This has the result that the free electrons move
randomly from the negative side to the positive side of the circuit. Fig.
1.3 shows this flow of electrons in a conductor.
Words &Terms
Conductor:a substance
through which an electric
current can flow
Component:a part of a
circuit, such as a cell or a
light bulb
applied voltage
electron
flow (current)
Remember, there is no such
thing as a positive electron!Don’t
make a fool of yourself in the
exam by referring to positive
electrons!
electron
current
Valence electrons:
electrons that are the
furthest away from the
nucleus of the atom
Potential:the energy that
charged particles in an
substance have because of
their position and the size
of their charge
Fig. 1.3 The flow of electrons in a conductor
Electrons further away from the nucleus are more easily removed than
those nearer to the nucleus, and conductors easily lose or replace their
free electrons. In practice, normal room temperature is enough to free
the electrons in a good conductor.
Unit 1.2: Electron flow in a conductor
01375 topic_01.indd 5
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The effect of external power on a conductor
Did you know?
An atom is very small. For
example, 1 cm3 (1 cm 1 cm 1 cm) of copper consists of
approximately 1024 atoms. An
electron is even smaller than an
atom. If only one out of every 100
atoms in a cubic centimetre of
copper is removed from the
metal, there will be a vast
number of electrons moving
freely in the copper at room
temperature. When this small
piece of copper is stretched out
in the form of a conductor, and
one side is made positive and the
other side negative, most of
these electrons will be pulled
towards the positive side, and
pushed from the negative side at
the same time. This movement of
electrons in one direction along
the conductor is known as
current flow.
The electric cell (see Fig. 1.2) has the ability to set electric energy free.
This is normally achieved by means of a chemical reaction within the
cell. The negative terminal has an excess of electrons while the positive
terminal has a shortage of electrons. When a conductor is connected
to the terminals, electrons will move through the conductor from the
negative terminal to the positive terminal. This conduction process will
last until the chemical reaction is exhausted.
The electrons within the cell move from positive to negative and in the
outer circuit from negative to positive. This movement of electrons from
negative to positive in the outer circuit is called electron current flow.
It is in contrast with conventional current flow, which flows from
positive to negative. This may sound confusing now, but it will soon
become clear!
When one electron starts to move, all the other electrons start to move
one by one. This can be compared to a locomotive pulling trucks:
when the locomotive starts pulling, all the trucks start moving, and
the second one moves to where the first one was, and so on. All the
trucks cover the same distance. The difference with the movement of
electrons is that the electrons are not linked together, but they move as
a result of the forces of attraction and repulsion.
Assessment activity 1.2
1.
What do we call the grouping method that the electrons and
protons in an atom strive to achieve?
2.
Draw a labelled diagram of the simplest atom you know.
3.
What do we call the connection between two components in an
electric circuit?
4.
Which particles in an atom carry the electrical charge? In which
direction do they move?
5.
State the three forms of matter.
6.
What do you understand by the term ‘conductor’ of electricity?
7.
What are the electrons that carry electricity between different
points in a circuit called?
8.
Redraw Fig. 1.3 and describe in your own words how electricity
flows through the material.
Electron current flow:current that
flows from negative to positive
9.
What is the movement of electrons through a material called?
What do we call the material through which the electrons move?
Conventional current flow:
current that flows from positive to
negative
10. How does a cell produce electrical energy?
Words &Terms
Current:the flow of electric
charge through a conductor. The
symbol for current is I and it is
measured in ampere (A)
Terminal:the point on a source of
potential difference (e.g. a battery)
where wires are connected to
make an electric circuit
Attraction:to bring something
closer
11. In which direction do the electrons move in a circuit and inside a
battery?
Repulsion:to push something
away
6
Topic 1, Module 1
01375 topic_01.indd 6
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12. Write a short paragraph in which you explain the flow of an
electrical current in a circuit outside the power source.
13. Apart from copper, name three other conductor materials that you
know about and say where they are used.
14. Which is smaller an electron or a proton?
15. What is the flow of electrons through a conductor called?
Unit 1.2: Electron flow in a conductor
01375 topic_01.indd 7
7
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Unit 1.3:Basic electric circuits
lamp
An electric circuit is a system of conductors and devices that convert
electric energy into other forms of energy such as light, heat, sound or
movement energy.
A functional electric circuit usually consists of four basic parts:
⦁ an energy source such as a battery
⦁ conductors or wires through which electrons flow
⦁ a control device such as a switch
⦁ a load.
switch
cell
(a)
lamp
(load)
Fig. 1.4 shows an electric circuit.
The load is a device or machine within which the actual energy
conversion takes place. An incandescent lamp, an electric motor
and the heating elements of a stove or bar heater are examples of an
electric load.
We normally get three types of diagrams in electricity and electronics:
switch
electron
current
(b)
cell
Fig. 1.4 An electric circuit
(a) Protoboard
⦁ a component or layout diagram
⦁ a block diagram
⦁ a circuit or schematic diagram.
Fig. 1.4 shows a component or layout diagram on the left and a circuit
diagram on the right.
In practice electric circuits can take a variety of forms. Fig. 1.5 shows
some of the most common circuits which you will use in your
practicals or encounter in the workplace.
(b) Veroboard
(c) Printed circuit board
Fig. 1.5 Different electric circuits
s
&Term
s
d
r
o
W
ular
tang
:a rec
s and
Matrix ment of row
e
g
arran
ns
colum
Fig. 1.5 (a) is a protoboard or a breadboard. The components are
simply plugged into the holes and the connections are made by means
of the sockets at the bottom and the wires at the top.
Fig. 1.5 (b) is a veroboard or a leo-board. This type of board has a
matrix of holes and copper strips at the bottom. Components are
mounted on top of the board and connections are made mainly at the
bottom of the board by means of the copper strips.
Fig. 1.5 (c) is a printed circuit board (or a PC board in short). This type
of board must be prepared by means of a special method, which will
be dealt with later. The components are then mounted on top of the
8
Topic 1, Module 1
01375 topic_01.indd 8
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board and soldered at the bottom where the copper tracts connect the
various components.
Voltage and current flow in an electric
circuit
Normally in electronics when we refer to a specific circuit we use a
schematic or circuit diagram. The schematic diagram uses ‘shorthand’
symbols called circuit symbols. Refer to Fig. 1.4 (b). Note the symbol
for the battery and electrical bulb. The connecting wires are shown
simply as straight lines because their resistance is small enough to be
negligible.
s
Words &Term
e ability of a
Resistance:th
mponent to
co
substance or
of electric
reduce the flow
mbol for
current. The sy
and it is
R
resistance is
ms ()
oh
in
d
measure
worth
Negligible:not
important
considering;un
Any electric circuit has three important characteristics:
⦁ There must be a source, in other words the applied voltage. Without
the source, no current can flow.
⦁ There must be a complete path for current to flow. In other words,
there must be an unbroken path from one side of the applied
voltage source through the external circuit and then returning to the
other side of the source.
⦁ The current path normally has resistance. Resistance can be included
in the form of the load or it may just be part of the wiring.
Take note that it is the current (electron flow) that moves through the
circuit and not the voltage. Voltage is also referred to as potential
difference, which you will learn more about in a later module.
The voltage across the filament in the bulb (see Fig. 1.4) causes the
electrons to flow from one side to the other, but it is the potential
difference across the filament that does the work of moving electrons
through the filament.
As the current flows in the circuit, electrons leave the negative terminal
of the cell and the same number of free electrons in the conductor are
returned to the positive terminal of the cell. In the process whereby
electrons are lost from the negative charge and gained by the positive
charge, the two charges would tend to cancel each other out. The
chemical action inside the cell separates electrons and protons all the
time to maintain the negative and positive charges at the terminals
of the cell to provide a potential difference. If there is no chemical
reaction inside the cell, current flow will stop. This is what happens
when cells or batteries stop producing electricity we say the battery
is flat!
Assessment activity 1.3
1.
What are the four functional parts of an electric circuit?
2.
Name and describe the three different types of diagrams that are
used in electronics.
3.
Which of the diagrams in Fig. 1.4 are normally used in electronics?
Why?
Think about it
The Department of Education
specifies in Subject Outcome 4
(covered in Module 4) that all
electrical units and symbols
must be in accordance with SI
units (as prescribed by the IEC International Electrotechnical
Commission). However, for some
components there is more than
one symbol. For example, the
symbol for resistance may be
either the rectangular symbol
) or the well-known
(
‘ zigzag’ symbol (
). If there
is more than one standard
symbol for a component, you
should use only one in a circuit
diagram. However, you should
know the other symbols as they
may be asked in the exam.
s
Words &Term
tential
Voltage:see po
difference
rence:the
Potential diffe
ectrical
el
in
e
differenc
n two
potential betwee
t. It is the
ui
rc
points in a ci
e one unit
ov
m
to
work done
n two points
charge betwee
it is
d
in a circuit an
lts (V). Also
vo
in
measured
ge
known as volta
Unit 1.3: Basic electric circuits
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erms
Words &T
g wire
a conductin
Filament:
t
a
th
ric bulb
in an elect
t
a
e
h
d
n
a
ght
gives off li
ric
ct
le
e
n
a
n
e
energy wh
gh it
sses throu
current pa
with
nt:glowing
Incandesce
heat
onal
n internati
SI units:a
f
units o
system of
e
ent (from th
m
re
u
meas
tème
French Sys
al)
n
o
Internati
10
4.
Describe the three types of circuit connections mentioned in the
text.
5.
Draw the circuit symbols of a battery, a bulb and a conductor.
6.
Draw a block diagram of an electric motor connected to a power
source.
7.
Name the three characteristics of an electrical circuit.
8.
Briefly explain why there is no current through a light bulb unless
it is connected across a source of energy.
9.
What is the difference between voltage and current?
10. In any circuit: (a) state two requirements for producing current;
(b) give the direction of electron flow.
Topic 1, Module 1
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