T770(E)(A7)T
NATIONAL CERTIFICATE
INDUSTRIAL ELECTRONICS N1
(8080641)
7 April 2017 (X-Paper)
9:00–12:00
This question paper consists of 7 pages and 1 formula sheet.
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T770(E)(A7)T
DEPARTMENT OF HIGHER EDUCATION AND TRAINING
REPUBLIC OF SOUTH AFRICA
NATIONAL CERTIFICATE
INDUSTRIAL ELECTORNICS N1
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.
Write neatly and legibly.
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T770(E)(A7)T
QUESTION 1
1.1
Complete the following sentences by filling in the missing word or words.
Write only the word or words next to the question number (1.1.1–1.1.10) in
the ANSWER BOOK.
1.1.1
Magnetic lines of force always enter the material at an angle of ...
to the surface.
1.1.2
Magnetic lines of force never ... one another.
1.1.3
The earth is an example of a ... magnet.
1.1.4
The property magnets possess is called ...
1.1.5
The number of poles on a horseshoe magnet is ...
1.1.6
The maximum value of a sine wave is ...
1.1.7
An alternating current generator will produce a ... wave.
1.1.8
When TWO hydrogen atoms combine they create a ... bond.
1.1.9
A positively charged atom is called a ...
1.1.10
An ... has a deficiency/shortfall of free electrons.
(10 × 1)
(10)
1.2
State TWO advantages of secondary cells.
(2)
1.3
Give THREE common faults that occur on capacitors.
(3)
1.4
Sketch the IEC symbols for each of the following components:
1.4.1
PNP transistor
1.4.2
Transformer with an iron core
1.4.3
Pre-set inductor
1.4.4
Capacitor
1.4.5
Fixed resistor
(5 × 1)
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(5)
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T770(E)(A7)T
QUESTION 2
2.1
Refer to FIGURE 1 below and calculate the following:
E = 200 V
R1 = 120 
R2 =180
R4 =180 
R3 =180 
FIGURE 1
2.2
2.1.1
The total resistance of the circuit
(7)
2.1.2
The total current flow
(3)
2.1.3
The voltage drop across R1
(1)
2.1.4
The colour code for the R4 resistor with a tolerance of 10%
(4)
A copper conductor is 120 m long and has a cross-sectional area of 6 mm 2 .
The resistivity of copper is 1,728 × 10 −6 Ωm.
Determine the resistance of the copper conductor.
2.3
Describe permanent magnet.
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T770(E)(A7)T
QUESTION 3
3.1
State THREE factors which determine the inductance of an inductor.
3.2
Describe the effect each of the factors below has on the resistance of a
conductor:
3.2.1
Length of the conductor
3.2.2
Cross-sectional area of the conductor
3.2.3
Temperature of the conductor
(3)
(3 × 2)
3.3
(6)
A circuit consist of TWO capacitors, C 1 and C 2 , with values of 1,2  F and
1,8  F respectively.
Calculate the following:
3.4
3.3.1
The charge across C 1 at 12 V voltage drop.
(3)
3.3.2
The total capacitance if the TWO capacitors are connected in
series
(4)
A transformer with 800 windings on the secondary coil has a secondary
voltage of 12 volts and a current flow of 1,5 amperes. The current flow
through the primary coil is 60 mA.
Calculate the primary voltage.
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T770(E)(A7)T
QUESTION 4
4.1
A tube filled with mercury has a resistance of 15 Ω at 0 °C.
If the tube is heated up to 20 °C, what will its resistance be? The resistance
temperature coefficient of mercury is 0,0042 Ω/°C.
(3)
4.2
State the left-hand rule for solenoids/coils.
(3)
4.3
Draw a labelled sketch to illustrate how a voltmeter is connected with a load
resistor (RL) in a circuit.
(3)
Describe how to test a transistor with an ohmmeter to find a base, emmiter
and collector.
(3)
4.4
4.5
Name the units in which each of the following is measured:
4.5.1
Electromotive force
4.5.2
Inductance
4.5.3
Potential difference
4.5.4
Frequency
4.5.5
Power
(5 × 1)
4.6
What effect does direct current have on a diode?
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(3)
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T770(E)(A7)T
QUESTION 5
5.1
Describe the reverse biasing condition of a diode.
(4)
5.2
Sketch a labelled full-wave rectifier circuit using a centre-tap transformer.
Also show a load resistor and a supply on your diagram.
(6)
5.3
Indicate whether the following statements are TRUE or FALSE. Choose the
answer and write only 'true' or 'false' next to the question number
(5.3.1–5.3.10) in the ANSWER BOOK.
5.3.1
The junction voltage of a germanium atom is 0,6 volts.
5.3.2
The output signal of an amplifier is smaller than the input signal.
5.3.3
A silicon atom has TWO valence electrons.
5.3.4
Holes are negative charge carriers.
5.3.5
Electrons in the outermost shell of an atom are called molecules.
5.3.6
When impurity atoms are added to the pure semi-conductor
material, the semi-conductor is said to be doped.
5.3.7
When TWO germanium atoms covalently bond with each other,
they form a crystal lattice structure.
5.3.8
A transistor consists of P- and N-type materials.
5.3.9
A transistor can be used as an amplifier.
5.3.10
A junction barrier is also called a depletion layer.
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(10 × 1)
(10)
[20]
TOTAL:
100
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T770(E)(A7)T
INDUSTRIAL ELECTRONICS N1
FORMULA SHEET
I=
V
R
I=
E
R+r
P=V×I
Rt = R1 + R2 + ... + Rn
1
1
1
1
=
+
+ ... +
Rt R1 R2
Rn
Ct = C1 + C2 + ... + Cn
1
1
1
1
=
+
+ ... +
Ct C1 C2
Cn
Q=C×V
Lt = L1 + L2 + ... + Ln
1
1
1
1
=
+
+ ... +
Lt L1 L2
Ln
Vp
Vs
=
Np
Ns
=
Is
Ip
R t = Ro (1 +  ot )
R=
ρ
A
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