Industrial Electronics N2

Industrial Electronics N2
Module 1:
Atom theory .................................................................................................................... 6
1.1 Introduction................................................................................................................................. 6
1.2 Matter ................................................................................................................................................ 6
1.2.1 Elements ........................................................................................................................................ 7
1.2.2 Compounds ................................................................................................................................. 7
1.2.3 Molecules ...................................................................................................................................... 7
1.3 The atom .......................................................................................................................................... 7
1.4 Covalent bonds.............................................................................................................................. 8
1.5 Electrical current flow ................................................................................................................... 9
Module 2:
Direct Current Theory ................................................................................................... 11
2.1 Introduction............................................................................................................................... 11
2.2 Electromotive force (emf) ......................................................................................................... 11
2.3 Definition of the ampere............................................................................................................ 11
2.4 Voltage ........................................................................................................................................... 12
2.4.1 Definition of the volt ................................................................................................................. 12
2.5 Resistance ...................................................................................................................................... 12
2.6 Ohm’s Law ..................................................................................................................................... 13
2.7 Power ............................................................................................................................................... 13
2.8 Resistor circuits .............................................................................................................................. 14
2.8.1 Resistors in series ........................................................................................................................ 14
2.8.2 Resistors in parallel .................................................................................................................... 14
2.8.3 Series-parallel combinations.................................................................................................. 15
2.9 Kirchoff’s laws ................................................................................................................................ 16
2.9.1 Current law (first law) ............................................................................................................... 16
2.9.2 Voltage law (second law) ..................................................................................................... 17
Module 3:
Alternating Current Theory.......................................................................................... 20
3.1 Introduction............................................................................................................................... 21
3.2 The cycle ........................................................................................................................................ 21
3.3 Frequency (f) ................................................................................................................................. 21
3.4 Period (t) ......................................................................................................................................... 21
3.5 Instantaneous value .................................................................................................................... 22
3.6 Average and rootmean (RMS) square values of a sinusoidal wave ............................ 24
3.6.1 Mid-ordinate rule method ...................................................................................................... 24
Gateways to Engineering Studies

1
3.6.2 Average and RMS value, calculated method ................................................................ 25

3.6.3 Resistor (R), Capacitor (C), Inductor (L) circuits ............................................................... 26
Resistor (R) ............................................................................................................................................. 26
Capacitor (C) ...................................................................................................................................... 26
Inductor (L) ........................................................................................................................................... 27
R-L circuits ............................................................................................................................................. 28
R-C circuits ............................................................................................................................................ 28
R-L-C circuits ......................................................................................................................................... 29
3.7 Phasors ............................................................................................................................................ 29
3.8 Resonance series circuits ........................................................................................................... 29
Module 4:
Semi-conductor Diodes .............................................................................................. 37
4.1 Introduction............................................................................................................................... 37
4.2 Silicon and germanium.......................................................................................................... 38
4.3 Valence electrons ....................................................................................................................... 38
4.4 Covalent bonds............................................................................................................................ 38
4.5 Doping............................................................................................................................................. 38
4.6 P-type material ............................................................................................................................. 38
4.7 N-type material............................................................................................................................. 39
4.8 Electron flow .................................................................................................................................. 40
4.9 Hole flow ......................................................................................................................................... 40
4.10 PN junction diode ...................................................................................................................... 41
4.10.1 Forward bias............................................................................................................................. 41
4.10.1 Reverse bias ............................................................................................................................. 42
4.11 Zener diodes ................................................................................................................................ 43
4.11.1 Properties of a zener diode ................................................................................................. 43
4.12 Varactor diodes ......................................................................................................................... 44
4.12.1 Properties .................................................................................................................................. 44
4.13 Photodiode .................................................................................................................................. 45
4.14 Light emitting diodes (LED) ..................................................................................................... 45
4.15 The halfwave rectifier with smoothing capacitor............................................................. 46
4.15 The full wave rectifier ................................................................................................................ 46
4.15.1 The centre tap rectifier without smoothing capacitor ................................................ 46
4.15.2 The centre tap rectifier with smoothing capacitor....................................................... 47
4.16 Bridge type rectifier (Four diodes)......................................................................................... 47
4.16.1 Without smoothing capacitor ............................................................................................. 47
4.16.2 With smoothing capacitor ................................................................................................... 48

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4.17 Calculations ................................................................................................................................ 48

Module 5:
Semi-conductor transistors ......................................................................................... 51
5.1 Introduction............................................................................................................................... 51
5.1.1 NPN transistor ............................................................................................................................. 52
5.1.2 PNP transistor .............................................................................................................................. 52
5.2 Operation of a transistor ............................................................................................................ 52
5.3 Basic amplifier circuit .................................................................................................................. 53
5.3.1 The transistor as a switch......................................................................................................... 54
5.4 Transistor circuit configurations ................................................................................................ 54
5.4.1 Common base .......................................................................................................................... 55
5.4.2 Common emitter ...................................................................................................................... 55
5.4.3 Common collector ................................................................................................................... 55
Module 6:
Measuring instruments ................................................................................................ 57
6.1 Introduction............................................................................................................................... 57
6.2 Lenz’s law ....................................................................................................................................... 57
MOVING COIL METER, ANALOGUE TYPE ................................................................................................ 58
6.3 The ampere meter ....................................................................................................................... 58
6.3.1 Internal arrangement of shunt resistor for the ampere meter ..................................... 59
6.3.2 Multi range ampere meter .................................................................................................... 60
6.4 The volt meter ............................................................................................................................... 60
6.4.1Internal arrangement of multiplier for the voltmeter ....................................................... 60
6.4.2 Multi range volt meter ............................................................................................................. 61
6.4 The ohmmeter............................................................................................................................... 61
6.5 The analogue multi-meter ......................................................................................................... 62
6.6 The digital multi-meter ................................................................................................................ 63
Module 7:
Transducers ................................................................................................................... 66
7.1 Introduction............................................................................................................................... 66
7.2 Light dependant resistor (LDR) ................................................................................................. 66
APPLICATION CIRCUIT .............................................................................................................................. 68
7.3 Thermocouples ............................................................................................................................. 68
CHARACTERISTIC CURVE .......................................................................................................................... 69
7.4 Bi-metallic strip .............................................................................................................................. 69
7.4.1Temperature sensitive transducer ......................................................................................... 69
7.5 Thermistor........................................................................................................................................ 69

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Module 8:
Syncro systems ............................................................................................................. 72
8.1 Introduction............................................................................................................................... 72
8.2 Lenz’s law ....................................................................................................................................... 72
8.2.1 Applications ............................................................................................................................... 72
8.3 Advantages of synchro systems over mechanical systems ............................................ 73
8.3.1 Acceptable symbols ................................................................................................................ 73
8.3.2 Operation.................................................................................................................................... 73
8.4 Wiring diagrams ............................................................................................................................ 73
Module 9:
The decibel ................................................................................................................... 76
9.1 Introduction............................................................................................................................... 76
9.2 Formula ........................................................................................................................................... 76

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5
Module 1 00
Learning Outcomes
When you have completed this module, as a learner you will be able to:
 Draw sketches of the atomic structure to illustrate universal properties

 Describe:
o Electron shells
o Free electrons
o Positive and negative charges
 Give an elementary description of:
o Conductors
o Insulators
o Non-active elements
1.1 Introduction
To understand electronics, you must first have an understanding of

atoms and basic atomic structure. This module discusses atomic
theory and explains the atom and its properties and how this
applies to conduction and insulation.
1.2 Matter
Matter is anything that has weight and takes up space. Matter cannot be
created or destroyed.
Matter exists in four different states, solid, liquid, gas and plasma. The earth and
anything on it is classified as matter.
Examples thereof:
 Solid matter are wood and stone
 Liquid matter are water and oil
 Gas matter are oxygen and helium
 Plasma consists of ionised particles such as lightning
Matter can change its state from one form to another. If ice is heated it will
become water and then steam. A solid has changed into a liquid form and then
into a gas.

6
Figure 1.1 Matter
1.2.1 Elements
Elements are used to construct matter. Examples of elements are gold, copper,
iron and silicon.
1.2.2 Compounds
A compound consists of two or more different types of elements. A compound
is formed when one or more elements react in a chemical way. For instance,
water is a compound that is made up of the elements oxygen and hydrogen.
1.2.3 Molecules
A molecule is the smallest part of a compound that still retains the characteristics
of the original compound without breaking up into individual atoms. A water
molecule is formed when two hydrogen atoms combine with one oxygen atom.
1.3 The atom

The atom is the smallest part of an element that can take part in a chemical
reaction. It has a nucleus that is build up of protons and neutrons, and has
electrons that revolve around the nucleus in definite orbits or shells.

7
Figure 1.2
The electrons in the orbits have a negative charge and they are attracted by
the protons in the nucleus, which have a positive charge. Each orbit can take
up only a certain number or electrons. The number of electrons in an orbit
determined by the formula 2n².
If the outermost orbit is incomplete (not completely filled with electrons), then
that orbit is called the valency band. The electrons inside the valency band are
called the valency electrons. The number of valency electrons in an atom is
called the valency number of the atom.
The protons in the nucleus have a positive charge, while the neutrons have no
charge at all. The number of electrons and protons in a neutral atom are the
same. The negative charge of electrons has the same amount of charge as the
positive charge of the protons. The atom will thus be electrically neutral.
The atomic number always indicates the number of protons or electrons in the
atom.
If the valency electrons are easily removed from the atom then the element to
which these atoms belong is called a conductor. Electrons which have left an
atom are called free electrons.
When electrons are removed from an atom, the atom becomes positively
charged. This positively charged atom is called a positive ion or a cation. When
electrons are added to an atom, it becomes negatively charged and is called
a negative ion.
If electrons of an atom are not easily removable, the element is called an

insulator. There exists elements which fall between conductors and insulators,
and they are called semiconductors.
1.4 Covalent bonds

Some atoms cannot exist on their own as a stable element. Such an atom must
combine with another similar atom or with a completely different atom to form
a certain type of material.

8
When two such atoms combine, a covalent bond is formed. In a covalent bond,
the two atoms involved each have one electron in the bond and they share
these two electrons with each other. Covalent bonds are very strong and
cannot easily be broken up.
Figure 1.3
1.5 Electrical current flow

Below is a metal bar which is connected to a cell. The chemical reaction that
takes place causes the free electrons in the metal bar to be attracted by the
positive terminal of the cell and to be repelled by the negative terminal.
This causes an electrical current to flow from the negative terminal of the cell to
the positive terminal. This type of current flow is referred to as electron current
flow. When referring to current flow as being from positive to negative, it is called
conventional current flow.
Figure 1.4
Activity 1.1
1. Define the following:

a. Matter
b. Elements
c. Compounds

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d. Molecules
e. The atom
f. Nucleus
g. Electrons
h. Conductor
i. Insulator
j. Covalent bond
2. Draw a model of an atom with an atomic number 28.
3. Draw a model of an atom which has 3 valence electrons.
4. Sketch two atoms in a covalent bond.
Self-Check
I am able to: Yes No

 Draw sketches of the atomic structure to illustrate universal
properties
 Describe:
o Electron shells
o Free electrons
o Positive and negative charges
 Give an elementary description of:
o Conductors
o Insulators
o Non-active elements
If you have answered ‘no’ to any of the outcomes listed above, then speak
to your facilitator for guidance and further development.

10
Module 2
Learning Outcomes
When you have completed this module, as a learner you will be able to
 Describe and illustrate circuit diagrams and calculations of current,

voltage and power for resistors in:
o Series
o Parallel
o Series – parallel combinations
 Explain the definitions of Kirchhoff’s first and second laws
 Draw circuit diagrams of Kirchhoff’s first and second laws
2.1 Introduction
Direct current can be defined that there is a fixed polarity of applied

voltage and the current flows in one direction. The unit of electrical
current is the ampere (A).Current flow is indicated by (I).
Definition: Potential Difference (PD)

The pd is the electrical pressure between any two points in a closed
circuit.
2.2 Electromotive force (emf)

The emf is that force that has the potential electrical energy to produce a current
flow in a circuit. EMF is measured in an open circuit. An open circuit does not
produce current flow.
2.3 Definition of the ampere

There are two common definitions for the ampere:
1. If a current of one ampere flows through a conductor 6,25 x 1018 electrons will
pass any point in one second.
2. One ampere is the constant current which, if maintained in two parallel
conductors of infinite length and one metre apart in a vacuum, will exert a
force of 2 x 10-7 newtons per metre.

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Basic unit Unit for small amounts Unit for large amounts
Pronounced Ampere Milli- Micro- Kilo- Mega-
ampere ampere ampere ampere
Abbreviation A mA 𝜇𝐴 kA MA
Multiplier 1 1 x 10-3 1 x 10-6 1 x 103 1 x 106
Table 2.1
Take Note:
1018 is a simple way of writing 1 followed by 18 zeroes which would be written

as 1, therefore, if a current of 1 Ampere is flowing through a conductor the
number of electrons passing a point every second would be
6,250,000,000,000,000,000 or 6,25 x 1018.
6,25 x 1018 electrons is called 1 coulomb (C) of electric charge. 1 ampere is

therefore 1 coulomb per second.
2.4 Voltage
Voltage is a general term for emf and pd, and are measured in volts (V). Voltage
is usually indicated by E or V in a circuit.
2.4.1 Definition of the volt

There are also two common definitions for the volt:
1. One volt is the pd between two points of a conducting wire carrying a

constant current of one ampere when the power dissipated between these
points is equal to one watt.
2. One volt is the potential difference across a resistance of one ohm when a
current of one ampere is passed through it.
Pronounced Volt Milli-volt Micro-volt Kilo-volt Mega-volt
Abbreviation V mV 𝜇𝑉 kV MV
Multiplier 1 1 x 10-3 1 x 10-6 1 x 103 1 x 106
Table 2.2
2.5 Resistance
The process where an electron travels slowly and with difficulty in a conductor, is
known as resistance. Resistance is expressed by R in a circuit and the unit of
resistance is the ohm (Ω).
Definition: Ohm
One ohm is the electric resistance between two points of a conductor
when a constant potential difference of one volt applied between

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these two points, produces a current flow of one ampere, and the
conductor is not the source of any emf.
2.6 Ohm’s Law

The amount of current flowing in any closed circuit is directly proportional to the
applied voltage and inversely proportional to the resistance.
Ohm`s law can be stated as a formula:
V
I
R
I is the amount of current in ampere (A).

V the applied voltage in volts (V).
R the resistance in ohms (Ω).
Pronounced Ohm Milli-ohm Micro-ohm Kilo-ohm Mega-
ohm
Abbreviation Ω mΩ 𝜇𝛺 kΩ MΩ
Multiplier 1 1 x 10-3 1 x 10-6 1 x 103 1 x 106
Table 2.3
2.7 Power
The amount of work done per second in an electrical circuit. The unit is watts (W),
the symbol is (P).
Power is generated by the applied voltage to a resistive circuit producing a

current flow. The current produces heat in the resistor which is referred to as
power dissipated in the resistor.
P  VI
P  I2  R
V2
P
R
Definition: Watt
One watt is the power which results in the production of energy at a
rate of one joule per second.
Pronounced Watt Milli-watt Micro-watt Kilo-watt Mega-watt
Abbreviation W mW 𝜇𝑊 kW MW
Multiplier 1 1 x 10-3 1 x 10-6 1 x 103 1 x 106
Table 2.4

13
2.8 Resistor circuits

2.8.1 Resistors in series
RTOTAL = R1 + R2 + .......
R1 R2
Figure 2.1
Worked Example 1
Find the total resistance of the circuit shown.
5 4 3
Figure 2.2
Solution:
RT = R1 + R2 + R3
=5 +4 +3
= 12
2.8.2 Resistors in parallel
1 1 1 R1  R 2
  OR R T 
R T R1 R 2 R1  R 2
R1
R2
Figure 2.3
Worked Example 2
Find the total resistance of the circuit shown.

14
5
10
Figure 2.4
Solution:
1

1 1
 10  5
RT =
RT 10 5 10  5
1 50
 0,3 OR 
RT 15
RT  3,33 RT  3,33
2.8.3 Series-parallel combinations
Worked Example 3
Find the total resistance of the circuit shown as well as the current flow through
the circuit. Also calculate the total power as well as the voltaqge and power
through the 3 Ω resistor.
4 5
2
I2
I1
6
3
ITOTAL
10V
Figure 2.5
Series circuit
RS  23
 5

15
RS  45
 9
Parallel circuit
9 6
RP 
9 6
 3,6 
RT  3,6  5
 8,6 
Total current flow
VT
IT 
RT
10

8,6
 1,16 A
Total power
PT  VT  I T
 10  116
,
 11,6 W
or
 I T  RT
2
PT
 116
, 2  8,6
 11,6 W
Voltage across 3Ω resistor
V3  I  R
 116
, 3
 3,48 V
Power across 3Ω resistor
P3  I2  R
 116
, 23
 4,04 W
2.9 Kirchoff’s laws

2.9.1 Current law (first law)
The algebraic sum of the currents flowing towards a point, is equal to the
algebraic sum of currents flowing away from that point.

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I1
I2 ITOTAL
I3
Figure 2.6
It =I1 +I2 +I3
2.9.2 Voltage law (second law)

The sum of voltage drops in a closed circuit is equal to the supply voltage.
R1 R2 R3
V1 V2 V3
VTOTAL
Figure 2.7
Vt = V1 + V2 + V3
Activity 2.1
1. Define the following

1.1 DC
1.2 EMF
1.3 PD
1.4 The ampere
1.5 Resistance
1.6 Ohm`s law
1.7 Power
1.8 Kirchoff`s laws
2. In the circuit shown in Figure 2.8, calculate the following:
2.1 the total resistance [1,53Ω]
2.2 the total current flow [6,52A]
2.3 the total power in the circuit [65,15 W]

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2.4 the voltage across the 3Ω resistor [4,55 V]

2.5 the current through the 3Ω resistor [1,52 A]
2.6 the power consumed in the 3Ω resistor [6,91 W]
2.7 the voltage across the 6Ω resistor [5,45 V]
2.8 the current through the 6Ω resistor [0,908A]
2.9 the power consumed in the 6Ω resistor [4,95 W]
2.10 the current through the 2Ω resistor [5 A]
3
5
10V
6 2
4
ITOTAL
Figure 2.8
3. Draw a fully labelled circuit diagram of a direct current power supply using
two diodes, a centre lap transformer and filter capacitor. Clearly show the
output waveforms before and after the filter capacitor.
4. Draw a labelled circuit diagram of a full-wave low voltage DC power supply
by using a step down transformer, four diodes, a filter circuit and a load
resistor. Show the polarities over the load resistor as well as the electron flow.
5. Refer to Question 4 and draw three labelled graphs indicating the
waveforms before the diodes, directly after the diodes and the output over
the load.
6. Refer to Figure 2.9 and determine the following:
6.1 The total resistance of the circuit [4Ω]
6.2 The total current of the complete circuit [3A]
6.3 The current I2 [1A]
6.4 The voltage over R2 [4]
6.5 The power consumed by the whole circuit [36W]
Figure 2.9

18
Self-Check

 Describe and illustrate circuit diagrams and calculations of
current, voltage and power for resistors in:
o Series
o Parallel
o Series – parallel combinations
 Explain the definitions of Kirchhoff’s first and second laws
 Draw circuit diagrams of Kirchhoff’s first and second laws
If you have answered ‘no’ to any of the outcomes listed above, then speak to
your facilitator for guidance and further development.

19
Module 3
Learning Outcomes
When you have completed this module, as a learner you will be able to:
 Demonstrate understanding by means of a graphical representation the

sine-wave with the aid of a rotating phasor
 Demonstrate calculations and definitions of:
o Frequency
o Peak value
o Peak to peak value
o RMS value
o Average value
o Crest factor
o Form factor
 Demonstrate calculations of instantaneous values with the aid of the
following formulae:
o e = 3m Sin 2 𝜋ft volts
o i = Im Sin 2 𝜋ft amps
 Demonstrate understanding by means of graphical representations and
calculations of non-sinusoidal quantities by means of the mid-ordinate rule
 Demonstrate understanding by means of graphical and phasor
representations of voltage and current to illustrate the effects with an
alternating current is applied to:
o Resistors
o Inductors
o Capacitors
 Explain by means of phase diagrams and calculations for a series circuit
containing R, L and C
o Current
o Voltage
o Impedance
o Resonant frequency
o Inductive reactance and
o Capacitive reactance

20
3.1 Introduction
When a conductor is rotated in a magnetic field as illustrated in

Figure 3.1, an emf will be induced. This emf will have a pulsating
affect which is referred to as alternating current. The current thus
moves forwards and backwards, which produces a continuous
change of polarity. This effect makes ac ideal for the operation of
transformers.
Armature
Brushes
Sliprings
Galvano-
meter
Figure 3.1
3.2 The cycle

One complete revolution of the conductor or armature 0º to 360º will produce a
cycle. One positive and one negative half cycle.
3.3 Frequency (f)

The number of cycles produced or generated in one second is known as
frequency. Frequency is measured in hert (Hz) or cycles per second. (c/s)
3.4 Period (t)

The time taken to produce one cycle is called a period.
Formula 1 1
t
f
Period (t) is measured in seconds.

21
+V
VP
360o
O
VP-P
-V
t
Figure 3.2
Vp-p = Voltage peak to peak.
t = period.
Vp = Vm = Peak Voltage or Maximum voltage.
= Lamda. Lamda is the length of a cycle and is measured in metre (m).
+ V = Positive voltage
-V = Negative Voltage.
3.5 Instantaneous value

When a cycle is produced, the armature of a generator rotated through an angle
of 360º or 2𝜋 radians. If the frequency is f, then the rotational frequency is 2𝜋f,
radians per second. Therefore () omega is the rotational speed of a armature
or axle.   2 f .
1800
To convert radians to degrees, multiply by

If an armature rotates through an angle of 00 in (t) seconds, then the
instantaneous value, voltage or current can be calculated.
Formula 1 1800
e  Em Sin 2 ft

Formula 2 e  Em Sin 0
Formula 3 1800 1800
  2 ft  t
 
Em = Maximum voltage value
(V).
e = Instantaneous voltage (V).
Formula 4 1800
i  Im Sin 2 ft

Formula 5 i  Im Sin  o
Im = Maximum current value (A).

i = Instantaneous current value (A).
t = Time in seconds (s).

22
Worked Example 1
A sinusodal wave has a frequency of 45Hz , and a maximum value of 20A.

Calculate
1. The angle of the armature 10ms after 00.
2. The instantaneous value 10ms after 00.
3. The time elapased at an angle of 360.
4. The current value at 360.
Solution:
1.
1800
  2 ft

1800
 2  4510  103

180 0
 2,827

= 1620
2.
i  Im Sin o
= 20 Sin 1620
= 6,18A
3.
 = 2ft
 = 36

= 36  = 0,628 radians
180

t
2f
0,628
=
2  ( 45)
= 0,0022s
= 2,2 ms
4.
i  Im Sin o
i = 20 Sin 36
= 11,76A

23
3.6 Average and rootmean (RMS) square values of a sinusoidal

wave
3.6.1 Mid-ordinate rule method
200V
00 300 600 900 1200 1500 1800

V 1 V2 V 3 V4 V 5 V6
Figure 3.3
Divide 180 of the sinusoidal wave into equally spaced ordinates as illustrated
and let n be the number of ordinates. Sample the value of the voltage or current
at each ordinate intersection. Table the results.
Worked Example 2
A sinusodal value has the following information.
Angle 00 300 600 900 1200 1500 1800

voltage 0 76 152 200 175 70 0
V1 = 45V V4 = 194V
V2 = 120V V5 = 126V
V3 = 190V V6 = 30V
Solution:
From this information V(AVE) and V(RMS) can be calculated.
V1  V2  V3  V4  V5  V6
VAVE 
(1) n
45  120  190  194  126  30

6
= 117,5V
V1  V2  V3  V4  V5  V6
2 2 2 2 2 2
V( RMS) 
(2) n

24
452  1202  1902  194 2  1262  302

V ( RMS ) 
6
= 133,5V
The same procedure is used to determine I(ave) and I(rms) values.
Formula 1 I1  I 2  I 3  I 4  I 5 ....... I n
I AVE 
n
Formula 2 I1  I 2  I 3  I 4 _ _ _ _ _ I n
2 2 2 2 2
I ( RMS) 
n
3.6.2 Average and RMS value, calculated method
Formula 1 V(ave) = Vm x 0,637

Formula 2 I(ave) = Im x 0,637
I(ave) = I(dc)
Formula 3 V(rms) = Vm x 0,707
Formula 4 I(rms) = Im x 0,707
Formula 5 RMSvalue
Form factor =
AVEvalue
Formula 6 Maximum value
Crest factor =
RMSvalue
A wave which has a form factor and crest factor value of less than 1,11 and 1,44
respectively is called a flat wave.
Worked Example 3
A sinusodal wave has the following information e = 120 sin 311,17t V.
Calculate
1. The maximum voltage value.
2. Vp-p
3. Vave
4. Vrms
5. Frequency (f)
6. Period (t)
Answers:
1. Vm = Vp = 120V
2. V(p-p) = 120 x 2 = 240V

25
3. VAVE  VM  0,637
 120  0,637
 76,44 V
4. VRMS  VM  0,707
 120  0,707
 84,84 V
5. 
f 
2
311,17

2
 50Hz
6. 1
t 
f
1

50
 0,02
 20 ms
3.6.3 Resistor (R), Capacitor (C), Inductor (L) circuits

These components behave differently in an ac circuit.
Resistor (R)
Current and voltage are in phase. Ohms law will apply in these circuits.
Formula 1 V
R 
I
V
R
I 18O 36O
I OO O O
VS
Figure 3.4
Capacitor (C)
In a pure capacitor circuit, the current leads the voltage by 90º.
Formula 1 1
Xc 
2fc
Where C = Capacitance in farads (F).

Xc
Capacitive reaction is the resistance a capacitor offers a circuit at
a specific frequency.

26
C 90O x
I y
V
VS
I
Figure 3.5
Inductor (L)
In a pure inductor circuit, the voltage leads the current by 90º.
Formula 1 XL = 2fL
Where L = Inductor value in Henry`s (H)
XL = Inductive reaction in ohms (Ω).

Inductive reaction is the resistance an inductor offers a circuit at a specific
frequency.
L
V
I V
0 0 0 0 0
I 0 90 180 270 360
900 I
VS
Figure 3.6
Definition: Impedance (Z)

The total resistance offered to a circuit by the reactance of an
inductor, a capacitor and a resistor and is measured in ohm.

27
R-L circuits
R L
ITOTAL
VS
Figure 3.7
Formula 1
Z  R2  XL
2
Formula 2 Vs
I 
Z
Where Z = Impedance (Ω) and Vs = Supply
voltage (V)
Formula 3 VS  VR  VL
2 2
Formula 4 VL = It x XL
Formula 5 VR = It x R
Formula 6 XL
  Tan1
R
R-C circuits
R C
ITOTAL VS
Figure 3.8
Formula 1 Z R2  XC
2
Formula 2 Vs
It 
Z
Formula 3 Vc = It x Xc
Formula 4 VS VR  VC
2 2
Formula 5 X
  Tan1 C
R

28
R-L-C circuits
C
R L
VS
Figure 3.9
Formula 1 Z  R L   X L  XC 
2 2
Formula 2 Vs
It 
Z
Formula 3 VS  VR   VL  VC 
2 2
Formula 4
  Tan1
XL  XC 
R
3.7 Phasors
Phasor diagrams are used to illustrate the relationships between the voltages,
currents or impedances and reactances in a circuit. There are basically three
types or illustrations or phasors.
XL VL IC
Z

R VR IR
 
VT
XC IT
VC IL
Figure 3.10
3.8 Resonance series circuits

Resonance is a condition that exists in a series RLC circuit when XL = XC, and R = Z,
VL = VC, the current and voltage will be in phase.
Formula 1 1
fR 
2 LC

29
Resonant frequency (FR) is the frequency where XL=XC. In a series R=Z. Current
will be at maximum value. No phase shift 𝜃 = 0º.
Worked Example 4
For the circuit shown in Figure 3.11, calculate:

1. Z
2. It
3. VR
4. Vc
5. The phase angle 𝜃
6. Draw the phasor diagram. (XC; R; Z)
7. Draw the phasor diagram (VC; VR; Vs)
20 100F
ITOTAL VS=220V
f=50HZ
Figure 3.11
Solution:
1. 1
XC 
2 fc
1

2  (50)(100  106 )
 31,83
Z R 2  XC
2
 202  31,832
 37,59
2. VS
It 
Z
220

37,59
 5,85 A
3. VR = It x R
= 5,85 x 20
= 117,05V
4. Vc = It x Xc
= 5,85 x 31,83

30
= 186,21V
5. XC
  Tan 1
R
1 31,83
 Tan
20
 57,86 o
6. 20
R
 = 57,86 0
31,83
Z
XC
7. VR=117,05V
 = 57,860
VS=220V
VC=186,21V
Worked Example 5
Determine the following for the circuit shown in Figure 3.12.

1. Xc
2. XL
3. Z
4. It
5. VC
6. VL
7. VR
8. Phase angle 𝜃
9. Draw the phasor diagram (XL; Xc; R; Z)

31
C L R
100mH 20
200F
Ib
VS=220V
f=50Hz
Figure 3.12
Solution:
1. 1
XC 
2 fc
1

2 (50)(200  106 )
 15,92
2. XL = 2fL
-3
= 2(50) (100 x 10 )
= 31,4
Z  R 2  X L  X C 
3. 2
 20 2   31,4  15,92
2
 25,29
4. Vs
It 
Z
220

25,29
 8,7A
5. Vc = It x Xc
= 8,7 x 15,92
= 138,18V
6. VL = It x XL
= 8,7 x 31,4
= 273,18V
7. VR = It x R
= 8,7 x 20
= 174V
8. Tan 1  XL  XC
 
R
Tan 115,48

20
 37,740

32
9. XL
XL-XC=15,48
Z

R
20
XC
Activity 3.1
1. Refer to the circuit and determine the following:
1.1 Xc [159,15]
1.2 Z [187,96]
1.3 It [1,17A]
1.4 VR [117V]
1.5 Vc [186,21V]
C
R
100
20F
VS=220V
f=50HZ
Figure 3.13
2. Determine the following:
2.1 Vs [28,28V]
2.2 L [23mH]
2.3 C [63,3]
2.4 R [10]
2.5 Z [14,14]

33
C
R L
VR=20V VL=30V VC=50V
IT=2A
V S=
f=100HZ
Figure 3.14
3. Determine the following:
3.1 R [3,75]
3.2 C [1273 F]
3.3 L [15,91mH]
3.4 FR [35,4Hz]
3.5 Draw the XL; XC; R; Z phasor diagram.
C R L
VC=10V VR=15V VL=20V

IT=4A
f=50HZ
XL
XL- XC =2,5
Z

R
3,75
XC
Figure 3.15
4. Determine the following for the circuit shown in Figure 3.16.
4.1 Z [161,9]
4.2 IT [O,62A]
4.3 VR [62v]
4.4 VC [78,94v]
4.5 Phase angle  [51,85O]

34
C=25F
R=100
IT
VS=100V
f=50HZ
Figure 3.16
5. Draw and label a sine wave of 720º with a peak value of 141,4 V and a
frequency of 100 Hz.
6. Calculate the following for the sine wave in Question 5:
6.1 Peak to peak value
6.2 The RMS value
6.3 Time (period of one cycle in seconds)
7. The equation for a certain alternating wave is given by the formula 3 =
150sin31,41tV. Use the formula to calculate the following:
7.1 The maximum or peak value for voltage [150V]
7.2 The average and RMS values [95,55V; 106,05]
7.3 The form and crest factors [1,11; 1,414]
7.4 The frequency of the waveform [5 Hz; 28,110 8V]
7.5 The instantaneous value of the voltage 6 and 12 milliseconds after
zero [55,225 5V]
Self-Check

 Demonstrate understanding by means of a graphical
representation the sine-wave with the aid of a rotating phasor
 Demonstrate calculations and definitions of:
o Frequency
o Peak value
o Peak to peak value
o RMS value
o Average value
o Crest factor
o Form factor
 Demonstrate calculations of instantaneous values with the aid of
the following formulae:
o e = 3m Sin 2 𝜋ft volts
o i = Im Sin 2 𝜋ft amps
 Demonstrate understanding by means of graphical
representations and calculations of non-sinusoidal quantities by
means of the mid-ordinate rule

35
 Demonstrate understanding by means of graphical and phasor

representations of voltage and current to illustrate the effects
with an alternating current is applied to:
o Resistors
o Inductors
o Capacitors
 Explain by means of phase diagrams and calculations for a series
circuit containing R, L and C
o Current
o Voltage
o Impedance
o Resonant frequency
o Inductive reactance and
o Capacitive reactance
If you have answered ‘no’ to any of the outcomes listed above, then speak to
your facilitator for guidance and further development.

36
Module 4
Learning Outcomes
On completion of this module, students should be able to:
 Demonstrate the crystal structure of pure germanium and silicon using

diagrams
 Describe:
o Valency electrons
o Doping
o Forming of P- and N-type materials
o Electron flow
o Hole flow
o Covalent bonds
 Describe with the aid of diagrams the PN-junction as applicable to diodes
when considering forward bias and reverse bias conditions
 Illustrate the difference between germanium and silicon diodes using
characteristic curves
 Describe the properties and characteristics of:
o Zener diodes
o Varactor diodes
o Photo diodes
o Light-emitting diodes
 Explain with the use of circuit diagrams the input and output wave forms o
the diode as:
o Half wave rectifier with a capacitor as a filter component
o Full wave rectifier using two and four diodes that include a capacitor as
a filter component
4.1 Introduction
Semiconductors are materials that are neither good conductors of

electricity nor are they insulators. The conductance of electricity is
achieved by means of thermally generated electrons and is
controlled solely by the temperature of the pure ‘intrinsic’
semiconductor material.

37
A semiconductor is a material having an electrical resistance higher than that

of good conductors such as copper or iron, but lower than that of insulators such
as glass or rubber.
A semiconductor has the following properties:

 As the temperature of the semiconductor rises, its electrical resistance
changes.
 When certain other substances are mixed with it, its electrical conductivity
rises.
 When struck by light, its resistance changes, and it emits light when an
electrical current is passed through it.
4.2 Silicon and germanium

Silicon (Si) and germanium (Ge) are the two most important semiconductors
used in the manufacturing of electronic components. The atoms of both these
materials are tetravalent. Tetravalent means that these atoms have four
valency electrons each. Pure or undoped semiconductor material is known as
intrinsic.
4.3 Valence electrons

Valence electrons are electrons found in the outermost unfilled electron shell of
a atom.
4.4 Covalent bonds

Covalent bonds are the sharing of the valence electrons between two atoms.
THE CRYSTAL LATTICE STRUCTURE

Figure 4.1
4.5 Doping
When semiconductor material is mixed with other chemicals to produce P-type
or N-type material. This is known as extrinsic or impure semi-conductor material.
4.6 P-type material

If a trivalent atom (an atom with three valence electrons) such as boron (B) or
indium is mixed with silicon or germanium, P-type material is produced. P-type

38
material is positive type material and is known as acceptor atom because it will
accept or attract electrons.
P-TYPE SEMICONDUCTOR
CRYSTAL LATTICE STRUCTURE
Figure 4.2
4.7 N-type material

If a pentavalent atom, such as phosphorus (P) or arsenic, is mixed with silicon or
germanium, N-type material is produced.
Definition: Pentavalent
An atom with five valence electrons.
N-type material is negative type material and is known as donor atoms, because
they will donate or give free electrons off to atoms attracting them.
Free electrons are electrons not joined in a atom structure. Free electrons are
free to conduct in current flow.
Free
electron
N-TYPE SEMICONDUCTOR
CRYSTAL LATTICE STRUCTURE
Figure 4.3

39
4.8 Electron flow
Figure 4.4
Electrons (é) have a negative charge and are attracted to the (+) side of a cell.
For every electron leaving the metal above one is give off or is replaced by the
(-) side of the cell.
4.9 Hole flow
Figure 4.5
Holes (+) are positions where electrons are housed. These holes (+) will attract
electrons. The hole does not move but electrons leaving a hole and filling
another gives the impression that holes are moved, thus hole flow.

40
4.10 PN junction diode
Figure 4.6
When P- and N- type material is joined to form one crystal structure. This PN
junction possesses rectification properties, and is known as a diode.
4.10.1 Forward bias
Figure 4.7
When a PN junction is forward biased, the depletion region disappears. The

battery is connected as illustrated. Conduction takes place due to electron
flow and hole flow. The forward voltage of a silicon diode is ± 0,6V and a
germanium diode is ± 0,3V. This is known as the threshold voltage. The threshold
voltage is the voltage required to overcome the virtual battery generated inside
the PN junction.

41
4.10.1 Reverse bias

When the PN junction is reverse biased, the depletion region increases. The
battery is connected as illustrated. No conduction takes place. No current can
flow. A diode which is reversed biased can be used as protection against
polarity reversal in electronic circuitry. Avalanche breakdown, is achieved
when the diode is forced into conduction by reverse biasing the diode with a
high voltage. This will destroy the diode.
Figure 4.8
Ge Si
Figure 4.9 PN Junction diode characteristic curve
Uses
1. Rectification.
2. Polarity reversal protection.
3. Filter circuit.
4. Back emf protection.
Symbol

42
Figure 4.10
4.11 Zener diodes

A zener diode is a special diode that serves as a voltage (pressure) relief valve.
It will conduct current, normally when forward biased. It will block current when
reversed biased. However, when a specific reverse bias voltage is reached, the
zener diode will conduct current.
Vz = Zener voltage
-V = Reverse bias area
SR = Safe conduction region
CHARACTERISTIC CURVE
Figure 4.11
4.11.1 Properties of a zener diode

This diode is used in reverse bias only.
Uses or application
Reference voltage or voltage regulation, eg if 9,1V zener diode is reverse biased
9,1V will be measured across the diode at all times.

43
RS
+
VS=12V
RL VZ=9V=VRL
-
APPLICATION CIRCUIT
Figure 4.12
Symbol
Figure 4.13
4.12 Varactor diodes

C = Capacitance value in F
-V = Reverse biased
25
Characteristic curve
F
100
-V
Figure 4.14
4.12.1 Properties
This diode is always reversed biased. To vary the reverse biased voltage will vary
the depletion area which will vary the capacitance value between the walls of
the depletion region. The larger the reverse voltage the lower the capacitance
value in (F) farads.
Uses
Tuning circuits such as in a (TV) television set.
Symbol
Figure 4.15

44
4.13 Photodiode
These diodes are reversed biased. This diode is so constructed that a window
allows incident light to fall on the PN junction. In no light conditions, no current
will flow. When light falls on the junction, the photodiode allows current to flow.
Symbol
A C
Figure 4.16
Application circuit
Figure 4.17
Uses
Light sensitive circuits, eg street lights, darkrooms etc.
4.14 Light emitting diodes (LED)

These diodes when forward biased give off light. When free electrons move
from one energy level to another they give off energy in the form of light known
as photons.
Symbol
Figure 4.18
Uses
(1) Indication circuits, e.g. on/off indications.
(2) 7-Segment display.
Application circuit

45
Figure 4.19
4.15 The halfwave rectifier with smoothing capacitor
Figure 4.20
Uses
Rectification properties. To convert ac to dc.
4.15 The full wave rectifier

4.15.1 The centre tap rectifier without smoothing capacitor
Figure 4.21

46
4.15.2 The centre tap rectifier with smoothing capacitor

Note that the current flows through the load resistor in the same direction,
therefore the polarity over RL is the same continuously.
Figure 4.21
4.16 Bridge type rectifier (Four diodes)

When the current source causes electrons to flow in a through the positive side
as show, the current will flow through D2, through the load (resistor). Through D4
and back to the negative side of the source. The other two diodes are reversed
biased and will block current flow.
4.16.1 Without smoothing capacitor
Figure 4.22

47
4.16.2 With smoothing capacitor
Figure 4.23
4.17 Calculations
FORMULA: (1) Halfwave Rectifier.
Vdc = Vp x 0,318
(11) Fullwave Rectifier.

Vdc = Vp x 0,637
Worked Example 1
A Bridge type rectifier has a Vp = 20 V, calculate the VDC.
Solution:
VDC = Vp x 0,637
= 20 x 0,637
= 12,74 V
Worked Example 2
A halfwave rectifier has a VDC value of 13,5 V. Calculate the Vp over the
secondary side of the transformer.
Solution:
VDC = Vp x 0,318
Vdc
VP 
0,318
13,5

0,318
 42 ,45V

48
Activity 4.1
1. Define the following :

1.1 Photo diodes
1.2 Doping
1.3 Light-emitting diodes
1.4 Free electrons
1.5 Valency electrons
1.6 Threshold voltage
1.7 Forward bias
1.8 Avalanche breakdown
1.9 Reverse saturation current
1.10 Reverse bias
1.11 Extrinsic semi-conductor
1.12 Intrinsic semi-conductor
2. Draw and label the characteristic curve of a 12V zener diode and explain
four of its characteristics.
3. Draw and label a circuit diagram of a half-wave rectifier fitted with a load
resistor of 100 Ω (RL) and a filter capacitor of 100 F (C). Show at least 720º
of the sinusoidal input and output waveforms.
4. Draw the characteristic curves of the following diodes:
4.1 Silicon diode
4.2 Varactor diode
5. Draw the symbols of the following diodes and state one function of each:
5.1 Zener diode
5.2 Varactor diode
6. Define the following terms:
6.1 Intrinsic semi-conductor
6.2 Extrinsic semi-conductor
7. Draw a labelled diagram indicating the biasing and current flow of an NPN
transistor.
Self-Check

 Demonstrate the crystal structure of pure germanium and
silicon using diagrams
 Describe:
o Valency electrons
o Doping
o Forming of P- and N-type materials
o Electron flow
o Hole flow
o Covalent bonds

49
 Describe with the aid of diagrams the PN-junction as

applicable to diodes when considering forward bias and
reverse bias conditions
 Illustrate the difference between germanium and silicon
diodes using characteristic curves
 Describe the properties and characteristics of:
o Zener diodes
o Varactor diodes
o Photo diodes
o Light-emitting diodes
 Explain with the use of circuit diagrams the input and output
wave forms o the diode as:
o Half wave rectifier with a capacitor as a filter component
o Full wave rectifier using two and four diodes that include a
capacitor as a filter component

50
Module 5
Learning Outcomes
By the end of the module you should be able to:
 Demonstrate understanding of the transistor as a PNP or NPN junction with

the use of sketches
 Explain the concepts of forward and reverse biasing as applicable to
emitter, base and collector
 Explain the operation of the transistor with the aid of I e = Ib + Ic (No
calculations)
 Demonstrate with diagrams how the transistor is employed as an amplifier
in the following configurations:
o Common emitter
o Common collector
o Common base
5.1 Introduction
A transistor regulates current or voltage flow and acts as a switch

or gate for electronic signals. A transistor consists of three layers of
a semiconductor material, each capable of carrying a current.
A semiconductor is a material such as germanium and silicon that conducts

electricity in a "semi-enthusiastic" way. It's somewhere between a real conductor
such as copper and an insulator (like the plastic wrapped around wires).

51
5.1.1 NPN transistor
Figure 5.1
VCC = Voltage closed circuit. (The supply voltage)
The transistor consists of three semiconductor layers. The base (B) and emitter (E)
must always be forward biased and the collector (C) reversed biased. This is for
both NPN and PNP transistors.
5.1.2 PNP transistor
Figure 5.2
5.2 Operation of a transistor

The current flows from the emitter (E) to the collector (C) and the amount of
current passing to the collector is controlled by the base (B). Formula: I E = IB + IC.
Another explanation for understanding purposes can be done by using a water
tap.
The water flowing from the supply to the bucket is controlled by the tap.

52
Figure 5.3
5.3 Basic amplifier circuit

To open and close or vary the current flow from the emitter to the collector, vary
the voltage VBE (Voltage base, emitter) between +0,4V to +0,9V, as illustrated.
0,7V 5V
Vce
0,6V Vrb
4V
0,5V
Figure 5.4
The value of RB is such that the DC voltage drop across RB is  0,6 V. If a person
speaks into the microphone (M) the microphone will produce a varying loss of
current which can be illustrated by VRB.
This current is applied to the base of the transistor which in turn will vary the flow
of current through the transistor from the emitter to the collector and will
produce a current to flow through loudspeaker illustrated by VCB.
The current produced will effect a sound in the loudspeaker which would be
amplified by the amplifier circuit.

53
Input voltage Vbe = 0,7 - 0,5 = 0,2V

Outputt voltage Vce = 6 - 4 = 2V
 Voltage gain of the amplifier is
Vo 2
Gi =   10( timesofgainof )
Vi 0,2
Vo 2
N  20Log  20Log  20dB
Vi 0,2
The input signal is small and the output signal large. The amplifier has amplified
the signal.
5.3.1 The transistor as a switch
Figure 5.5
If the switch is closed the VBE is forward biased and the transistor will conduct.
The globe will light up. The transistor is saturated. This means that maximum
current will flow through the transistor.
In an amplifier circuit, the current varies through the transistor, and is not in
saturation.
5.4 Transistor circuit configurations

There are three basic configurations in which a transistor can be used.

54
5.4.1 Common base
Figure 5.6
Applications
This circuit is used in voltage amplifier circuits.
5.4.2 Common emitter
Figure 5.7
Applications
This circuit is used in a power amplifier circuit.
5.4.3 Common collector
Figure 5.8

55
Applications
This circuit is used as a current amplifier circuit.
Activity 5.1
1. Draw and label the block diagram of a PNP transistor. Label the charge
carriers and explain the equation, IE = IB + IC.
2. Draw and label the circuit diagram of an NPN transistor in a common
collector amplifier circuit.
3. Draw and label a common base amplifier using an NPN transistor, showing
the most essential components.
4. Draw and label a single-stage NPN-transistor amplifier in a common emitter
configuration. A microphone and a loudspeaker must be connected to the
input and output terminals.
Self-Check

 Demonstrate understanding of the transistor as a PNP or NPN
junction with the use of sketches
 Explain the concepts of forward and reverse biasing as
applicable to emitter, base and collector
 Explain the operation of the transistor with the aid of Ie = Ib + Ic
(No calculations)
 Demonstrate with diagrams how the transistor is employed as
an amplifier in the following configurations:
o Common emitter
o Common collector
o Common base

56
Module 6
Learning Outcomes
 Describe, by means of a sketch, how the moving coil meter is employed as

a volt meter and an amp meter
 Demonstrate how to change the range of the above-mentioned metres
using circuit diagrams and calculations of resistor values
 Demonstrate a circuit diagram that is suitable for measuring resistance
 Demonstrate by means of a circuit diagram of an analogue multi-meter
with a maximum of three scales per quantity to measure the following:
o Current
o Voltage
o Resistance
 Describe an introduction of the digital metre in respect of:
o Advantages
o Uses
o Scales
6.1 Introduction
A measuring instrument is a device which is used to evaluate an

unknown quantity.
6.2 Lenz’s law

The direction of an induced emf is always such that it tends to set up a current
opposing the motion and the change of magnetic flux responsible for producing
that emf.

57
MOVING COIL METER, ANALOGUE TYPE
Figure 6.1
The value under test is passed through the coil which interrupts the magnetic
flux of the magnet, which forces the pointer to a different position. The scale is
calibrated to read off the correct value.
6.3 The ampere meter

An ampere meter is a meter which is used to measure the amount of current
flowing in a circuit. The current that will give a full scale deflection (fsd) will
normally be between 1mA and 20mA.
A shunt resistor (RSH) will be placed in parallel to the coil winding to prevent
damage to the meter if a large current (IT) is to be measured. The shunt resistor
is usually composed of a few resistors placed on parallel and is selectable so as
to vary the range of the ampere meter.
The shunt resistor (RSH) value can be calculated as follows:
Formula
IM  RM
(1) RSH  Rsh = Shunt resistor
ISH
Im = Current through the meter
(2) Ish = It - Im
Rm = Internal resistance of the meter
IM  RM
(3) RSH  Ish= Current through Rsh
IT  IM
It = Current being measured

58
6.3.1 Internal arrangement of shunt resistor for the ampere meter
Figure 6.2 An ampere meter is always connected in series with the circuit.
Worked Example 1
A current value of 7A is to be measured. The ampere meter has a internal

resistance of 2Ω and a full scale deflection of 10mA. Calculate:
1. the value of the shunt resistor.
2. the value of current through the shunt resistor.
Solution:
It = 7A
Rm = 2
Im = 10mA = 10 x 10-3
(1) the value of the shunt resistor

IM  RM
RSH 
IT  IM

 
10  103  2
7  10  103
0,02

6,99
 2 ,86m
(2) the value of current through the shunt resistor

ISH = IT - IM
= 7 - (10 x 10-3)
= 6,99mA

59
6.3.2 Multi range ampere meter

It
I1 I2 I3 I4 Im
Rsh1 Rsh2 Rsh3 Rsh4

M
mA
A
nA A
Figure 6.3
6.4 The volt meter

A volt meter is always connected in parallel with the circuit under test. The same
type of moving-coil meter is used as in the ampere meter. A resistor connected
in series to the meter is to prevent the current from exceeding the full-scale
current rating and damaging the meter.
This resistor is called a multiplier and is used to make the meter Multi-rangeable.
The multiplier can be calculated as follows.
Formula
VT
(1) R S   RM RS = Multiplier
IM
VT = Voltage under test
IM = Current through coil

(2) VT = IM (RS + RM)
RM = Resistance or coil
6.4.1Internal arrangement of multiplier for the voltmeter
Figure 6.4

60
Worked Example 2
A voltmeter has a full scale deflection of 15mA and a internal resistance of 5

Ω. Calculate the value of the resistor to measure a full scale voltage of 50V.
Solution:
VT = 50V, RM = 5Ω, IM = 15mA = 15 x 10-3A
VT
RS   RM
IM
50
 5
15  103
 3333,33  5
 3328,3
 3,328k
6.4.2 Multi range volt meter
V Rs1
mV Rs2
S1
+ Rs3 Im
V
Figure 6.5
6.4 The ohmmeter

A moving - coil meter can be used to measure the value of an unknown
resistance (Rx).

61
Figure 6.6
Rl = Current limiting resistor.

Ro = Variable zero adjustment resistor.
Rx = Resistance under test.
B = Battery or power source of meter.
6.5 The analogue multi-meter

This analogue can be used as a multipurpose meter to measure current, voltage
and resistance with multi- ranging selectivity. The meter is also known as a (AVO
meter).
V
R1
S1
mV
R2
V V
R3
S1
A
A


R4 R5 R6
x7
S4 R7
Rv M
B
x10
+ S3 R8 A mA A
S2
x100
R9
_
Figure 6.7

62
Caution: When using a multi-meter for testing current in a circuit

Multi-meters have a small internal resistance in the circuit for
measuring electric current. Therefore, a multi-meter should never be
connected in parallel to a circuit as a large amount of current will
flow and destroy the multi-meter. The multi-meter must be
connected in series with the circuit.
Precautions to be taken when using an analogue meter

 Always select the highest scale first and then decrease the scale if
necessary.
 Never leave the meter on the ohm scale. This could cause the batteries to
run down.
 Before any measurements are made, the meter must be set to zero.
 Prevent polarity reversal.
Caution: When using a multi-meter for testing voltage in a circuit

Multi-meters, when used to measure voltage, have a high internal
resistance, therefore, a multi-meter should never be connected in
series to a circuit. The multi-meter must be connected in parallel with
the circuit.
Caution: When using a multi-meter for measuring resistance in a

circuit
Multi-meters, when used to measure resistance, can be damaged if
the current in the circuit is flowing. Therefore the current must be
switched off or the voltage disconnected.
6.6 The digital multi-meter

This type of multi-meter uses a numerical readout. The display is usually a LCD
(liquid crystal display) or 7 segment LED (Light emitting diodes). This meter has
a high level of accuracy, and can automatically select a suitable range.
Uses
 Current meter
 Volts meter
 Ohms meter
 Continuity tester
 Diode tester
 Test (HFE) current gain of transistors
Scales
Auto-ranging = automatically selects a suitable range.
Advantages
Advantages of the digital multi-meter over a analogue multi-meter.

63
 Zero - adjustment is not necessary.

 Indicates polarity reversal.
 Polarity reversal protection.
 Overload protection.
 Auto-ranging
 High degree of accuracy.
 Response speed is increased.
 More robust.
Activity 6.1
1. Name two advantages of a digital- multi-meter over an analogue multi-

meter and three uses thereof.
2. A moving coil meter has a full-scale deflection of 10 mA and an internal
resistance of 200 Ω.
Draw the circuit diagram and calculate the value of the multiplier resistor
that would enable the meter to measure 20 V. [1800 Ω].
3. Mention three precautions to be taken when using an ohmmeter.
4. A meter has a full scale deflection of 15mA and an internal resistance of
15 0Ω. Calculate:
(a) Value of the multiplier resistor to measure a full scale voltage of 200V.
(b) Draw and label the circuit. [Rs = 14,52kΩ].
+ Im=15mA
Rs=14,52 k
Vt=220V V
Rm=150
Figure 6.8
5. A current of 45A must be measured. The meter has a internal resistance

150Ω and a scale deflection of 20mA.
Calculate:
(a) The value of the shunt resistor. [66,696mΩ].
(b) The value of the current through the shunt. [44,98A]
(c) Draw the circuit.

64
+ It
Im=20mA
Rsh Rm=150
Figure 6.9
Self-Check

 Describe, by means of a sketch, how the moving coil meter is
employed as a volt meter and an amp meter
 Demonstrate how to change the range of the above-
mentioned meters using circuit diagrams and calculations of
resistor values
 Demonstrate a circuit diagram that is suitable for measuring
resistance
 Demonstrate by means of a circuit diagram of an analogue
multi-meter with a maximum of three scales per quantity to
measure the following:
o Current
o Voltage
o Resistance
 Describe an introduction of the digital metre in respect of:
o Advantages
o Uses
o Scales

65
Module 7
Learning Outcomes
 Describe the operating principle, construction and characteristic curves of:

o Light dependant resistors (LDR)
o Thermo couples
o Bi-metallic strip
o Thermistors
7.1 Introduction
A transducer is a device that converts one form of energy to another.

Some common everyday transducers used around the house are an
electric stove, fridge, kettle, microwave oven, motor car etc.
7.2 Light dependant resistor (LDR)

This is a light sensitive resistor. The resistance varies with a change in light intensity.
This component is made from photo-conductive semi-conductive materials such
as cadmium selenide (CdSe), Cadmium sulfide (Cds) and lead sulfide (infra - red
sensitive).
Figure 7.1 Components

66
The resistance value of a LDR varies with the amount of light that falls on it. A
LDR is a light dependant resistor.
It is used for external lighting systems that are only activated at night, camera
light meters, etc.
The LDR has a ‘window’ under which lies a grid of material that is sensitive to
light.
R
Light intensity
Figure 7.2 Characteristic curve
Figure 7.3 Symbol

67
APPLICATION CIRCUIT
Figure 7.4 When light falls on the (LDR) its resistance decreases, causing the
transistor to conduct, the relay operates and the high current light will switch on.
This simple circuit is used in street lighting, or to switch on a light when the sun
goes down.
7.3 Thermocouples
A temperature sensitive transducer. This transducer consists of two different
metals such as nickel- chrome and nickel- aluminium. If the two metals are
joined together, as illustrated and the two junctions are at different
temperatures, a potential difference exists between two metals.
The value is dependant on the temperature differences. The voltage value is in

the region of a few milli-volts. A voltmeter, which is calibrated in ºC is used to
indicate the temperature.
Figure 7.5 Construction

68
CHARACTERISTIC CURVE
Figure 7.6
7.4 Bi-metallic strip

7.4.1Temperature sensitive transducer
Two metals, iron and brass, riveted together at room temperature. These two
metals have different expansion coefficients. When the metals are heated, the
device bends to one side, when chilled in bends to the other side.
If an indicator is attached to the device and a scale is used, calibrated to read

temperature, we have the oldest temperature transducer ever used.
Construction
Figure 7.7
Uses
A simple circuit can be build using the bi-metallic strip to close an alarm circuit
when a fire breaks out.
7.5 Thermistor
A temperature sensitive resistor. This components resistance varies with a charge
of temperature. The component is either (NTC) negative temperature
coefficient, resistance decreases if temperature increases, or (PTC) positive
temperature coefficient, resistance increases with a increase in temperature.

69
Figure 7.8 Characteristic curve
Figure 7.9 Symbol
Application
In this application the thermistor is mounted to the heat-sink of the transistor and
prevents thermal runaway of the amplifier and causes distortion.
Figure 7.10
Activity 7.1
1. Define a transducer.
2. Describe each of the following transducers:
2.1 bimetal strip
2.2 thermistor
2.3 LDR

70
2.4 thermocoule
3. Draw, label and explain application circuits of the transducers in Question 2.
4. Describe briefly, by using labelled sketches, the difference between a
bimetallic strip and a thermocouple transducer.
5. Draw labelled circuit diagram symbols of the LDR and the photo diode.
Briefly describe the main differences between them and the working
principle of each.
Self-Check

 Describe the operating principle, construction and
characteristic curves of:
o Light dependant resistors (LDR)
o Thermo couples
o Bi-metallic strip
o Thermistors

71
Module 8
Learning Outcomes
 Explain the definition of Lenz’s Law

 Describe the properties, uses, operating principles and draw a circuit
diagram of a synchro system with standard coupling
 Draw circuit diagrams of a synchro system illustrating the couplings for:
o 180 phase shift
o 240 phase shift
o Rotors that rotate in opposite directions
8.1 Introduction
A syncro system is the electrical equivalent of the transferring of

mechanical displacement over a distance. A synchro system
synchronises two or more systems by one control over a distance by
an electrical signal.
An example of this is a transmitter and receiver of a model, remote controlled
aeroplane. The transmitter or controller controls the flight of the aeroplane.
If the rotor in the transmitter is moved, the magnetic field on the rotor is affected
and in turn transmits an error signal to the receiver which forces the rotor of the
receiver to the desired position.
8.2 Lenz’s law

When a magnetic field cuts through a coil it induces a current to flow which will
generate a magnetic field. This magnetic field will oppose the original field.
8.2.1 Applications
 Remote controlled model aeroplane.
 Control of dam sluice gate.
 Control of ships rudder.
 Control of space ships.
 Remote control of microwave dishes.

72
8.3 Advantages of synchro systems over mechanical systems

 The transmitter and receiver can be far apart.
 Contact between the transmitter and receiver can be over electrical wires,
radio frequency, radar, microwave and infra-red.
 Very little electrical energy is used.
 No mechanical friction between transmitter and receiver.
8.3.1 Acceptable symbols

Always label all the diagrams in full.
Figure 8.1
8.3.2 Operation
Control between the transmitter and receiver is done by means of a magnetic
field. If the rotor of the transmitter is moved, a magnetic field forces the receiver
to move. The direction of the resultant movement by the receiver will depend on
the wiring of the rotor (R) and the stators (S).
8.4 Wiring diagrams

Tx Rx
Figure 8.2 In-phase displacement
If the transmitter is turned 45º clockwise the receiver will follow and also turn 45º
clockwise.

73
2400 PHASE SHIFT DISPLACEMENT

Tx
Tx Rx
Tx
Figure 8.2 240º phase shift displacement
This can be achieved by connectors as illustrated

Tx Rx
Figure 8.2 Opposite direction phase shift displacement
If S1 and S3 are connected between the transmitter and receiver this will give
an opposite direction displacement. When the transmitter is turned 45º
clockwise, the receiver will turn 45º anticlockwise.
Tx Tx
Figure 8.2 180º phase shift displacement
This is achieved by connecting R1 and R2 between the transmitters. If the

transmitter’s rotor is held at 0º the receiver will be on 180º. If the transmitter is
moved 45º clockwise, the receiver will follow and move 45º clockwise to the
position (180º + 45º) = 225º.
Activity 8.1
1. Define Lenz`s law.

2. Define a synchro system.

74
3. Give three advantages of a synchro system with reference to a mechanical

system.
4. Name three applications of syncro systems.
5. Explain in your own words why Lenz`s law is applicable to syncro systems.
6. Draw and label a sketch of a syncro system to illustrate 240º displacement
between the transmitter and receiver.
7. Draw the acceptable symbols of syncro systems.
8. Make a neat sketch showing the coupling between a transmitter and an
indicator to give a 180° phase shift.
9. State two requirements of a synchro-system to operate successfully.
Self-Check

 Explain the definition of Lenz’s Law
 Describe the properties, uses, operating principles and draw
a circuit diagram of a synchro system with standard coupling
 Draw circuit diagrams of a synchro system illustrating the
couplings for:
o 180 phase shift
o 240 phase shift
o Rotors that rotate in opposite directions

75
Module 9
Learning Outcomes
 Describe the definition of a decibel

 Calculate gains and losses in terms of :
o Power
o Voltage
o Current
9.1 Introduction
The unit (dB) decibel is 1/10 of a Bel. This unit is used to express the
ratio between two signals, output and input signal. If the output
signal is larger than the input signal, the signal has been amplified. If
the output signal is smaller than the input signal, the signal has been
attenuated.
PI N PO N = Amplifier or attenuater
P = Power
9.2 Formula
PO
N  10 log
Pi
Worked Example 1
An electronic network has a output power of 60mW and a input power of 16mW.
Calculate the gain or loss of the network.
PO
N  10 log
Pi

76
60  10 -3
 10 log
16  10 -3
= 10 log 3,75
= 5,74 dB
The circuit is an amplifier and the signal has undergone a gain.
Worked Example 2
An electronic network has a output voltage of 2,5V and a input voltage of 12V.
The input and output impedance is 600.
Calculate:
(a) Po
(b) Pi
(c) Io
(d) Ii
(e) The gain or loss of the amplifier in (dB)
R1 = R0 = 600 V1 = 12V, V0 = 2,5V

a)
2
V0
P0 
RO
2,52

600
 0,0104W
 10,4 mW
(b)
2
V1
Pi 
R1
12 2

600
= 0,24W
= 240mW
(c)
V0
I0 
R0
2,5

600
= 4,167mA
(d)

77
V1
I1 
R1
12

600
= 20mA
(e)
PO
N  10 log
Pi
10mW
 10 log
240mW
= (-) 13,80 dB
The electronic network is a attenuator, (dB) is a ratio and is never express as (-).
Worked Example 3
A electronic network has a gain of 26 dB. The input power (Pi) = 27mW.
Calculate the output power (Po).
P
N  10 log O
Pi
PO
26dB  10 log
27 mW
26 PO
 log
10 2,7  10 3
PO
anti log 2,6 
2,7  10 3
PO
398,11 
2,7  10 3
PO  398,11  2,7  10 3
 1,07W
Activity 9.1
1. Define the decibel.

2. A 200 mV input to an amplifier produces a current of 2 A in a loudspeaker
which has a 4Ω impedance. The input impedance is 300 Ω.
Calculate:
2.1 The input power (Pi) [0,133mW]
2.2 The output power (Po) [16W]
2.3 The input current (Ii) [0,66mA]
2.4 The output voltage (Vo) [8V]
2.5 The gain of the amplifier in dB (N) [50,79dB]

78
3. A 20mV input to an amplifier produces a current of 200mA in a loudspeaker

which has a 4Ω impedance. The input impedance is 30 Ω.
Calculate the gain of the amplifier in dB(N) [N = 40,8dB]
4. An amplifier has an output of 10 w and an input power of 10 mW. Calculate
the gain or loss of the amplifier in decibel (dB). [N = 30dB (gain)]
5. An amplifier has a gain of 100. Determine this gain in the unit decibel. [N =
20dB]
Self-Check

 Describe the definition of a decibel
 Calculate gains and losses in terms of :
o Power
o Voltage
o Current

79
Table of C
Past Examination Papers
APRIL 2012
NATIONAL CERTIFICATE
INDUSTRIAL ELECTRONICS N2
(8080602)
28 March (X-Paper)
09:00 – 12:00
This question paper consists of 5 pages, a 1-page diagram sheet and a 3-page
formula sheet.

80
TIME: 3 HOURS
MARKS: 100
__________________________________________________________________
INSTRUCTIONS AND INFORMATION
1. Answer ALL the questions.
2. Read ALL the questions carefully.
3. Number the answers according to the numbering system used in this question
paper.
4. Keep subsections of questions together.
5. RULE OFF on completion of each question.
6. Use ONLY IEC symbols and units when answering the question paper.
7. ALL sketches must be neat and labelled, using a pencil and a ruler (NOT
freehand sketches).
8. NO red or green ink may be used.
9. 22
Use 𝜋 as 3,142 and NOT as
7
10. Write neatly and legibly.

___________________________________________________________________

81
QUESTION 1
1. Define the following terms:
1.1 Matter (2)
1.2 Conductor (2)
1.3 Covalent bond (2)
1.4 Resonance (2)
1.5 Thermistor (2)
[10]
QUESTION 2
2. Refer to FIGURE 1 (on the attached DIAGRAM SHEET) and calculate the
following:
2.1 The value of the resistor R1 (2)
2.2 The power consumed by the resistor R2 (2)
2.3 The total resistance of the circuit (6)
[10]
QUESTION 3
3 Refer to FIGURE 2 (on the attached DIAGRAM SHEET) and calculate the
following:
3.1 The value of the capacitor (2)
3.2 The value of the inductor (2)
3.3 The total impedance of the circuit (3)
3.4 The total current (2)
3.5 The voltage drop across the capacitor (2)
3.6 The phase angle (3)
[14]
QUESTION 4

82
4.1 An alternating current waveform has a peak-to-peak value of 300 V
Calculate the following:
4.1.1 The maximum or peak value for voltage (2)
4.1.2 The average and RMS values (2)
4.1.3 The form and crest factors (2)
4.2 The equation for a certain alternating wave is given by the formula:
e = 150 sin 3,41 tV. Use the formula to calculate the following:
The instantaneous value of the voltage 6 and 12 milliseconds after zero. (6)
[12]
QUESTION 5
5.1 Draw the symbols of the following diodes and give ONE use of each:
5.1.1 Zener diode (2)
5.1.2 Varactor diode (2)
5.2 Draw and label the expected Input and output waveforms of the rectifier in
FIGURE 3 (attached DIAGRAM SHEET). The transformer is connected to
220 V/50 Hz. (6)
[10]
QUESTION 6
6.1 An ammeter can measure 500 mA full scales. The meter movement requires
a current of 1 mA to show a full-scale deflection. The internal resistance of
the meter is 500 Ω.
6.1.1 Calculate the shunt resistance (up to THREE decimal points). (3)
6.1.2 Draw and label the circuit of the ammeter described in QUESTION 6.1.
(5)
6.2 State THREE precautions which must be taken when measuring current with
an ammeter. (3)
[11]

83
QUESTION 7
With reference to the theory of TRANSISTORS, answer the following questions:
7.1 Draw a labelled circuit symbol for an NPN and a PNP transistor. (6)
7.2 Name THREE types of amplifiers. (3)
[9]
QUESTION 8
8.1 Define a transducer. (2)
8.2 Discuss the operating principle of the following transducers:
8.2.1 Thermistor (2)
8.2.2 Bimetal strip (2)
8.3 Calculate the gain of an amplifier that produces a voltage of 10 V over

a 15 Ω loudspeaker when a current of 12 mA is applied to the input.
The input impedance of the amplifier is 10 000 ohms (6)
[12]
QUESTION 9
9.1 Define Lenz's Law. (5)
9.2 Make a neat labelled sketch of a synchro system showing the connections
for the transmitter and receiver to turn in the same direction. (6)
9.3 State THREE advantages of a synchro system over a mechanical system. (3)
[12]
TOTAL: 100

84
DIAGRAM SHEET

85
FORMULA SHEET

86

87

88
Marking Guidelines
APRIL 2013
(8080602)
This marking guideline consists of 6 pages

89
QUESTION 1
1.1 Matter is anything that has weight and takes up space and cannot be created (2)
or destroyed. √√
1.2 Material that allows current to flow through it. √√ (2)
1.3 The sharing of valency electrons by two atoms. √√ (2)
1.4 When XL= X. In a series circuit R = Z and the current will be at its maximum (2)
value. √√
1.5 A thermistor is a temperature-sensitive resistor. √√ (2)
[10]
QUESTION 2
2.1 𝑉 12 (2)
𝑅1 = = 1,2 = 10 𝛺 √√
𝐼
2.2 𝑃 = 𝑉 𝑥 𝐼 = 12 𝑥 0,6 = 7,2 𝑊 √√ (2)
2.3 12
𝑅2 = 0,6 = 20 𝛺 √
𝑉5 = 𝑉𝑡− (𝑉3 + 𝑉4 ) = 12 − (1,2 + 3,6) = 7,2 𝑉 √
7,2
𝑅5 = 0,6 = 12 𝛺 √
6
𝑅 = 2 + 12 + 20 = 10 𝛺 √
𝑅𝑡 = 10//10 = 5𝛺 √√ (6)
NOTE: double ticks at the end of the ANSWER imply a tick for the preceding step. [10]
QUESTION 3
3.1 1
𝑋𝑐 =
2𝜋𝑓𝑐
1
63,662 = 2𝜋 𝑥 50 𝑥 𝐶 √
(2)
𝐶 = 50 𝜇𝐹 √
3.2 𝑋𝐿 = 2𝜋 𝑓𝑙: 15,708 = 2𝜋 𝑥 50 𝑥 𝐿 √

𝐿 = 15,708 / 314,159 = 0,05 𝐻 √ (2)
3.3 2 (3)
𝑍𝑇 = √102 + (63,662 − 15,708) = 48,985 𝛺 √√√
3.4 𝑉1 100 (2)

𝐼𝑇 = = = 2,04 𝐴 √√
𝑍1 48,985
3.5 𝑉𝑐 = 𝐼𝑡 𝑥 𝑋𝑐 = 2,04 𝑥 63,662 = 129,96 𝑉 √√ (2)

90
3.6 𝜃 = cos −1 10/48,985 √√ (3)

= 78,56° √
[14]
QUESTION 4
4.1.1 Maximum peak = 300/2 = 150 V √√ (2)
4.1.2 RMs = 0,707 x maximum = 0,707 x 150 = 106,05 V √

Average value = 0,637 x maximum = 0,637 x 150 = 95,55 V √ (2)
4.1.3 Form = 106,05/95,55 = 1,11 √

Crest = 150/106,05 = 1,414 √ (2)
4.2 180
𝑒6𝑚𝑠 = 150 sin 31,41 𝑥 6 𝑥 10−3 𝑥 = 28,08 𝑉 √√
𝜋
180
𝑒12𝑚𝑠 = 150 sin 31,41 𝑥 12 𝑥 10−3 𝑥 = 55,12 𝑉 √√ (6)
𝜋
[12]
QUESTION 5
5.1.1
(2)
5.1.2
(2)

91
5.2
(6)
[10]
QUESTION 6
6.1.1 (3)
6.1.2
(5)
6.2 Connect in series with load

Observe correct polarities
Start with highest scale
Switch off power before connecting meter
Never touch probes at tips, only at insulation. (3)
(Any THREE)
[11]

92
QUESTION 7
7.1
(6)
7.2 Common emitter (3)

Base
Collector
(ONE mark each)
[9]
QUESTION 8
8.1 A device that converts one form of energy into another. √√ (2)
8.2.1 The resistance will decrease as the temperature increases. √√ (2)
8.2.2 When heating two different types of metal which are fastened on top of each
other, the combined metal strip will bend because of the change in
temperature. √√ (2)
8.3 Po = V2/R = 102/15 = 6,67 W √√

Pin = 12 x R = (12 x 10-3)2 x 10 000 = 1,44 W √√
N = 10 Log Po/Pin = 10 Log (6,67/1,44) = 10 Log 4,632 = 6,657 db √√ (6)
[12]
QUESTION 9
9.1 Whenever a magnetic field cuts through a coil and induces a voltage in the
coil, causing a current to flow, that current will in turn generate its own
magnetic field which will oppose the original induced magnetic field. (3)

93
9.2
(6)
9.3 Transmitter and receiver can be far apart. Very little electrical energy is used.
Contact between the two systems can be by means of radio, telemetering or
wires. Quantity can be controlled. Large values can be transmitted when it is
combined with a server system. √√√ (Any THREE) (3)
[12]
TOTAL: 100

94
Past Examination
Table of C Papers
NOVEMBER 2012
(8080602)
9 November (X-Paper)
09:00 – 12:00

95
This question paper consists of 5 pages, a 1-page diagram sheet and a 3-page formula
sheet.
TIME: 3 HOURS
MARKS: 100
__________________________________________________________________
paper.
4. Keep subsections of questions together.
5. RULE OFF on completion of each question.
6. Use ONLY IEC symbols and units when answering the question paper.
7. ALL sketches must be neat, using a PENCIL and a ruler. NOT freehand.
9. 22
Use 𝜋 as 3,142 and NOT as 7

____________________________________________________________

96
QUESTION 1
1. Define the following:
1.1 Impedance (2)
1.2 Photodiodes (2)
1.3 Doping (2)
1.4 Threshold voltage (2)
1.5 Covalent bonds (2)
[10]
QUESTION 2
2 Refer to FIGURE 1 (on the attached DIAGRAM SHEET) and calculate the
following:
2.1 The total current flowing in the circuit (5)
2.2 The voltage drop across the R1 resistor (4)
2.3 The current flowing through R2 resistor (2)
2.4 The power used in the 2 0 resistor (2)
[13]
QUESTION 3
3 A 10 0 resistor, 198 IJF capacitor and 10 mH inductor are connected in series.

The circuit is connected to a 50 V/50-Hz supply.
Calculate the following:
3.1 The inductive reactance (2)
3.2 The capacitive reactance (2)
3.3 The impedance of the circuit (2)
3.4 The current flowing in the circuit (2)
3.5 The phase angle between the voltage and current (2)
[10]

97
QUESTION 4
4.1 Draw and label a sine wave of 720° with an RMS value of 220 V with a
frequency of 50 Hz. (4)
4.2 Calculate the following for the sine wave in QUESTION 4.1:
4.2.1 The maximum value (2)
4.2.2 The average value (2)
4.2.3 The peak-peak value (2)
4.2.4 The time period in seconds (2)
[12]
QUESTION 5
5.1 Draw labelled circuit symbols for the following:
5.1.1 A PN-junction diode (2)
5.1.2 Zener diode (2)
5.1.3 Varactor diode (2)
5.2 With the aid of neat labelled circuit diagrams, explain the following as
applicable to PN-junction diodes: (4)
Forward bias
5.6 Draw a fully labelled circuit diagram of a half-wave rectifier using a step down
transformer, a diode, capacitor and a load resistor. (6)
[16]
QUESTION 6
6.1 State FOUR advantages of the digital meter as compared to the analog
meter. (4)
6.2 State THREE precautions which must be taken when measuring voltage with
a multimeter. (3)
[7]
QUESTION 7

98
With reference to the theory of TRANSISTORS, answer the following

questions:
7.1 Draw and label a single-stage NPN transistor amplifier in a common emitter
configuration. A microphone and a loudspeaker must be connected to the
input and output terminals. (6)
7.2 Name the THREE classes of amplifiers. (3)
[9]
QUESTION 8
8.1 Name THREE most commonly used examples of transducers. (3)
8.2 Describe the difference between a light dependent resistor and a thermistor. (4)
8.3 The input power to a system is 100 mW and the power it delivers at the output (6)
is 10 mW. Calculate the system's power loss.
[13]
QUESTION 9
9.1 Draw the TABLE in FIGURE 2 on the attached DIAGRAM SHEET A in the
ANSWER BOOK and show the coupling between the transmitter and receiver
for a 240° phase shift. (6)
9.2 State FOUR applications of synchronous systems. (4)
[10]
TOTAL: 100

99
DIAGRAM SHEET A

100
FORMULA SHEET

101

102

103
Marking Guidelines
NOVEMBER 2012
(8080602)
This marking guideline consists of 6 pages.

104
QUESTION 1
1.1 Impedance is the total resistance offered to a circuit by the inductor, capacitor
and resistor. √√ (2)
1.2 Photodiodes are diodes which offer a high resistance in the dark, but when
incident, light falls onto the pn-junction, the diodes resistance decreases. √√ (2)
1.3 A process achieved by adding impurity atoms to silicon or germanium to

increase the materials conductivity. √√ (2)
1.4 The forward bias voltage required to overcome the depletion region of the
diode for silicon diodes its 0, 6. √√ (2)
1.5 Covalent bonds is the sharing of valency electrons by two atoms. √√ (2)
[10]
QUESTION 2
2.1 15 𝑥 10
𝑅// = = 6𝛺 √
15+10
20 𝑥 20
𝑅// = = 10𝛺 √
20+20
10 𝑥 6
𝑅// = 10+6 = 3,75 𝛺 √
𝑅𝑇 // = 3,75 + 2 = 5,75 𝛺 √
12
𝐼𝑇 = 5,75 = 2,08 𝐴 √ (5)
2.2 𝑉3 = 2,08 𝑥 2 = 4,174 𝑉 √√

Voltage across 𝑅1 = 12 − 4,174 = 7,826 𝑉 √√ (4)
2.3 7,826 (2)

𝐼2 = = 0,391 𝐴 √√
20
2.4 𝑃 = 2,08 𝑥 2 = 4,16 𝑊 √√ (2)
[13]
QUESTION 3
3.1 𝑋𝐿 = 2𝜋𝜋𝑓𝑥 2𝜋 𝑥 50 𝑥 10 𝑥 10−3 = 3,14 𝛺 √√ (2)
3.2 1 (2)
𝑋𝐶 = = 16,08 √√
2 𝑥 3,141 𝑥 50 𝑥 198 𝑥 10−6
2
3.3 𝑍𝑇 = √102 + (16,08 − 3,14 = 167,557 𝛺 √√ (2)
3.4 𝐼𝑇 =
𝑉𝑡
𝑍𝑡
=
50
167,557
= 0,298 𝐴 √√ (2)

105
3.5 𝑅 10 (2)
𝜑 = cos−1 = cos−1 = 86,57 √√
𝑧 167,557
[10]
QUESTION 4
4.1
(4)
4.2.1 RMS = 0,707 x Maximum = 0,707 x Max

220 = 0,707 x Max
Max = 220,0,707
= 311,174 V √√ (2)
4.2.2 Average value = 0,637 x Maximum = 0,637 x 311,174 V (2)

= 198,217 V √√
4.2.3 Peak to Peak = 2 x Maximum = 2 x 311,174 (2)

= 622,348 V √√
4.2.4 𝐼 𝐼 (2)
𝑡= = = 0,02 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 √√
𝑓 50
[12]
QUESTION 5
5.1.1 (2)
5.1.2 (2)
5.1.3 (2)
5.2 Forward bias

106
Positive terminal connected to the anode and negative terminal to the

cathode, cause current flow through the diode. (4)
5.3
(6)
[16]
QUESTION 6
6.1 They are more robust/More accurate; No parallax error

A constant high impedance is offered on all voltage ranges
Overload is indicated/Reverse polarity is indicated/Auto ranging available (4)
5.2 Always connect a voltmeter across the component/The correct polarity

should always be observed/Always take loading effect of voltmeter into
account If uncertain use highest scale and decreases if necessary (3)
[7]
QUESTION 7
7.1
(6)
5.2 Class A, B and C (3)

[9]

107
QUESTION 8
8.1  A loudspeaker
 A microphone
 A solar cell (3)
8.2 LDR – This is a light sensitive resistor. The resistance varies with change in
light intensity. √√
Thermistor – This is a temperature sensitive resistor. The resistance varies

with a change in temperature. (NTC or PTC) √√ (4)
8.3 𝑃0
𝑁 = 10 𝐿𝑜𝑔
𝑃1
10 𝑚𝑊
= 10𝐿𝑜𝑔 100 𝑚𝑊 √√
(6)
= −10 𝑑𝐵(𝑙𝑜𝑠𝑠 𝑜𝑟 𝑛𝑒𝑔𝑎𝑡𝑖𝑣𝑒 𝑔𝑎𝑖𝑛) √√√√
[13]
QUESTION 9
9.1
5 marks for each correct coupling. 1 extra mark if all correct – 6 marks (6)
9.2 Control of power tools/Control positioning of gun turrets/Control of dam sluice

gates
Remote positioning of communication systems/Remote control of model cars
Angular displacement of ships rudder/Rapid and accurate transmission of
information between/Equipment and stations/Control the course of missiles
(4)
[10]
TOTAL: 100

108
Table of C
Past Examination Papers
APRIL 2012
(8080602)
22 March (X-Paper)
09:00 – 12:00

109
This question paper consists of 5 pages, 1 diagram sheet and a 3-page formula
sheet.
TIME: 3 HOURS
MARKS: 100
__________________________________________________________________
paper.
4. Keep sub-sections of questions together.
5. Rule off across the page on completion of each question.
6. Use only IEC symbols and units throughout.
7. ALL sketches must be neat, using a pencil and a ruler NOT freehand.
9. 22
Use 𝜋 as 3,142 and NOT as
7

______________________________________

110
QUESTION 1
1. Indicate whether the following statements are TRUE or FALSE. Choose the
answer and write only 'true' or 'false' next to the question number (1.1 - 1.10)
in the ANSWER BOOK.
1.1 A decibel is one tenth of a bel. (1)
1.2 A synchro system is the electrical equivalent of mechanical transfer of

information over a long distance. (1)
1.3 The voltmeter must always be connected in parallel with the load. (1)
1.4 The resistance of the NTC thermistors decreases as the temperature

increases. (1)
1.5 The common emitter amplifier has a 180° phase shift. (1)
1.6 The mid-ordinate rule is used to calculate the RMS values of sinusoidal wave
forms. (1)
1.7 The sum of the currents flowing towards a point is equal to the sum of the
currents flowing away from the same point. (1)
1.8 Electrons on the outer energy level are called valence electrons. (1)
1.9 Varactor diodes are most commonly used in FM and TV receiver circuits. (1)
1.10 Doping is the addition of impurities to pure semi-conductor materials. (1)
[10]
QUESTION 2
2. Refer to FIGURE 1 (attached DIAGRAM SHEET) and calculate the following:
2.1 The total resistance of the circuit (4)
2.2 The current flowing through the 100 Ω resistor (4)
2.3 The voltage drop across the 20 Ω resistor (3)
2.4 The total power consumed by the circuit (3)
[14]
QUESTION 3
3. Refer to FIGURE 2 (attached DIAGRAM SHEET) and calculate the following.

111
3.1 The value of the capacitor (3)
3.2 The value of the inductor (3)
3.3 The resonant frequency (4)
3.4 The voltage drop across the inductor and the capacitor (4)
[14]
QUESTION 4
4.1 Draw neat, labelled characteristic curves of the silicon and germanium diodes
on the same axis. (6)
4.2 Draw a fully labelled circuit diagram of a direct current power supply using
FOUR diodes, step down transformer and filter capacitor. (5)
[11]
QUESTION 5
5. Refer to the table below and make use of the mid-ordinate rule to determine
the following:
5.1 The mid-ordinates of the voltage (3)
5.2 The average value (3)
5.3 The RMS value (3)
5.4 The crest factor (2)
5.5 The form factor (2)
(The above values are ordinates and not the mid-ordinate values)
[13]
QUESTION 6
6.1 State TWO precautions when using an ampere meter. (2)
6.2 State THREE advantages of digital meters over analogue meters. (3)
6.3 A Voltmeter has a full scale defection of 5 mA and an internal resistance of

100 ohms. Calculate the value of the resistor that would enable the meter to

112
measure a voltage of 5 V. Also draw a neat, labelled circuit diagram to show

where this resistor should be connected. (5)
[10]
QUESTION 7
7. Answer the following questions with reference to transistor theory. Write only
the answer next to the question number (7 .1 - 7.3) in the ANSWER BOOK.
7.1 Draw and label a circuit symbol of a PNP silicon transistor. (3)
7.2 Name the THREE classes of transistor amplifiers. (3)
7.3 Draw a labelled circuit diagram of a common BASE amplifier circuit which
uses an NPN transistor. (3)
[9]
QUESTION 8
8.1 Explain the operation of the following transducers:
8.1.1 Thermo couple (3)
8.1.2 Bi-metal strip (3)
5.2 Calculate the gain or loss of an amplifier with an input of 1 W and an output
of 100 mW. (4)
[10]
QUESTION 9
9.1 Define Lenz's law. (5)
9.2 Draw a neat, labelled symbol of a synchro. (3)
9.3 State THREE advantages of synchro-systems over mechanical systems. (3)
[9]
TOTAL: 100
DIAGRAM SHEET

113

114
FORMULA SHEET

115

116

117
Marking Guidelines
APRIL 2012
(8080602)
The marking guideline consists of 5 pages.

118
QUESTION 1
1.1 True (1)
1.2 True (1)
1.3 True (1)
1.4 True (1)
1.5 True (1)
1.6 False (1)
1.7 True (1)
1.8 True (1)
1.9 True (1)
1.10 True (1)
[10]
QUESTION 2
2.1 20 𝑥 5
𝑅// = 20 ÷5 = 4𝛺 √
𝑅𝑆 = 4 𝛺 + 60 𝛺 + 36 𝛺 = 100 𝛺 √
𝑅// = (100 𝑥 100)/200 = 50𝛺 √
𝑅𝑡 = 50 𝛺 + 50 𝛺 = 100 𝛺 √√
𝐼𝑇 = 50/100 = 0,5 𝐴 (4)
2.2 I2 = It − I4 = 0,5 A − 0,25 A = 0,25 A √√√√ (4)
2.3 𝑉20𝛺 = 𝐼 𝑥 𝑅 = 0,05 𝑥 20 = 1𝑉 √√√ (3)
2.4 𝑃 = 𝐼 2 𝑥 𝑅 = 0,52 𝑥 100 = 25 𝑊 √√√ (3)

𝑃 = 𝑉 2 /𝑅 = 502 /100 = 25 𝑊
[14]
QUESTION 3
3.1 𝑋𝑐 = 1/2𝜋𝑓𝑐 (3)

𝐶 = 1/2𝜋𝑋𝑐 = 1/2𝜋𝑥50𝑥10 = 318,59𝜇𝐹 √√√
3.2 𝑋𝐿 = 2𝜋𝑓𝐿 (3)

𝐿 = 10/2𝜋𝑥50 = 31𝑚𝐻 √√√

119
3.3 1 (4)
𝑓𝑜 = = 1/0,01997 = 50𝐻𝑧 𝑋𝐶 = 𝑋𝐿
2𝜋√𝐿𝐶
3.4 𝑉𝑡 (4)
𝐼𝑇 = = 200/100 = 2𝐴 √√
𝑍𝑡
𝑉𝐿 = 2𝑥10 = 20𝑉 √
𝑉𝑐 = 2𝑥10 = 20𝑉 √
[14]
QUESTION 4
4.1
(6)
4.2
(5)
[11]
QUESTION 5
5.1 MID-ORDINATES IN VOLT: 11,25/50/112,5/122,5/72,5/25 √√√ (3)
5.2 𝑣𝑅𝑀𝑆/𝐺𝐸𝑀 = 11,25 + 50 + 112,5 + 122,5 + 72,5 + 25/6 = 65,625 𝑉 √√√ (3)
5.3 𝑣 +𝑣 +𝑉 1 2 2 (3)
𝑉𝑊𝐺𝐾 = √ 2 𝑛2 2 = 77,642 𝑉 √√√
5.4 Form = 77,64/65,63 = 1,183 √√ (2)

Crest = 150/77,64,63=1,932 √√ (2)
[13]

120
QUESTION 6
6.1 The ammeter must be connected in series with the load. Always start with the
highest scale. Switch of the power before measuring. (2)
6.2 More sensitive. More robust. No parallax error. No guessing. Overload (3)
indication.
6.3 𝑅𝑆 = 𝑉/𝐼𝑚 − 𝑅𝑚 = 5/5𝑚𝐴 − 100 = 1000 − 100 = 900𝛺 (5)
[10]
QUESTION 7
7.1
(3)
7.2 A,B AND C (3)
7.3
(3)
[9]
QUESTION 8
8.1 The thermo couple is a temperature device consisting of two metals joined at
the ends. When one end is heated a potential difference is set up across the
two ends. This potential difference is proportional to the difference in

121
temperature between the two ends. Materials used in the manufacture of

thermo-couples include nickel-chrome and nickel-aluminium. √√√ (3)
8.2 The bi-metal strip instead of generating a voltage it indicates only a change (3)
in temperature. The two Metals have different expansion coefficients
therefore it will bend when it is heated. √√√
8.3 𝑃0 (4)
𝑁 = 10 𝐿𝑜𝑔 = 10𝐿𝑜𝑔 100 𝑚𝑤 = −10 𝑑𝐵 √√√√
𝑃1
[10]
QUESTION 9
9.1 When a magnetic field cuts through a coil it induces a current to flow which
will generate a magnetic field. This magnetic field will oppose the original
field. (5)
9.2
(3)
9.3 Receiver and transmitter can be far apart. Contact can be by means of radio,
telemetering or wires. Very little energy is used. (3)
[9]
TOTAL: 100

122

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Industrial Electronics N2

Gateways to Engineering Studies

3.6.2 Average and RMS value, calculated method ................................................................ 25

Gateways to Engineering Studies

4.17 Calculations ................................................................................................................................ 48

Gateways to Engineering Studies

Gateways to Engineering Studies

Icons used in this book

Icon Description Icon Description

Assessment / Activity Multimedia

Demonstration/ observation Presentation/ Lecture

Did you know? Read

Experiment Site visit

Group work/ discussions,

Keywords Think about it

Gateways to Engineering Studies

 Draw sketches of the atomic structure to illustrate universal properties

To understand electronics, you must first have an understanding of

Gateways to Engineering Studies

Figure 1.1 Matter

1.3 The atom

Gateways to Engineering Studies

If electrons of an atom are not easily removable, the element is called an

1.4 Covalent bonds

Gateways to Engineering Studies

1.5 Electrical current flow

1. Define the following:

Gateways to Engineering Studies

I am able to: Yes No

Gateways to Engineering Studies

 Describe and illustrate circuit diagrams and calculations of current,

Direct current can be defined that there is a fixed polarity of applied

Definition: Potential Difference (PD)

2.2 Electromotive force (emf)

2.3 Definition of the ampere

Gateways to Engineering Studies

1018 is a simple way of writing 1 followed by 18 zeroes which would be written

6,25 x 1018 electrons is called 1 coulomb (C) of electric charge. 1 ampere is

2.4.1 Definition of the volt

1. One volt is the pd between two points of a conducting wire carrying a

Gateways to Engineering Studies

2.6 Ohm’s Law

I is the amount of current in ampere (A).

Power is generated by the applied voltage to a resistive circuit producing a

Gateways to Engineering Studies

2.8 Resistor circuits

Find the total resistance of the circuit shown.

2.8.2 Resistors in parallel

Find the total resistance of the circuit shown.

Gateways to Engineering Studies

2.8.3 Series-parallel combinations

Gateways to Engineering Studies

2.9 Kirchoff’s laws

Gateways to Engineering Studies

It =I1 +I2 +I3

2.9.2 Voltage law (second law)

1. Define the following

Gateways to Engineering Studies

2.4 the voltage across the 3Ω resistor [4,55 V]