NATIONAL CERTIFICATE

ELECTROTECHNICS N4

30% ICASS NO: 1

LECTURER Mr BD NGQOLWAZANE

MODERATOR Mrs MASANGO

DATE 06 MARCH 2024

TOTAL 50

DURATION 1H30M

This question paper consists of 7 pages and formula sheet.

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 NATIONAL CERTIFICATE
ELECTROTECHNICS N4
TIME: 2 HOURS MARKS:
61

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. Questions may be answered in any order but subsections of questions must be kept
together.

5. Start each question on a new page.

6. Only use a black or blue pen.

7. Write neatly and legibly

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QUESTION 1: PRINCIPLES OF ELECTRICITY

1.1 Various options are given as possible answers to the following questions. Choose the
answer and write only the letter (A–E) next to the question number (1.1.1–1.1.10) in the
ANSWER BOOK.

1.1.1 The strength of a direct current is directly proportional to the potential difference and
inversely proportional to the resistance of the circuit:

A Kirchhoff's law
B Ohm's law
C Lenz's law
D Faraday's law
E Joule's law

1.1.2 From his research, he deduced that the heat generated in a circuit is proportional to the
square of the current, the resistance of the circuit, and the time during which the current
flows:

A Kirchhoff's law
B Ohm's law
C Lenz's law
D Faraday's law
E Joule's law

1.1.3 In any complete loop within a circuit, the sum of all voltages across components that
supply electrical energy must be equal to the sum of all voltages across the other
components in the same loop:

A Kirchhoff's law
B Ohm's law
C Lenz's law
D Faraday's law
E Joule's law

1.1.4 The direction of an induced EMF is always such that it tends to set up a current opposing
the motion or the change of flux responsible for inducing that EMF:

A Kirchhoff's law
B Ohm's law
C Lenz's law
D Faraday's law
E Joule's law

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1.1.5 The magnitude of the induced EMF is directly proportional to the rate of change of flux
linkages:

A Kirchhoff's law
B Ohm's law
C Lenz's law
D Faraday's law
E Joule's law

1.1.6 Any network that has two terminals and consists of resistances, voltage sources and
current sources can be replaced by a single current source in parallel with a single
resistance:

A Superposition theorem
B Fleming's left-hand rule
C Norton's theorem
D Right-hand grip rule
E Thevenin's theorem

1.1.7 Any network with two terminals consisting of resistances, voltage sources and current
sources can be replaced by a single voltage source with its open-circuit EMF in series
with a single resistance:

A Superposition theorem
B Fleming's left-hand rule
C Norton's theorem
D Right-hand grip rule
E Thevenin's theorem

1.1.8 In a network that contains more than one voltage or current source, the current flow of
each source can be determined independently, and the current flow in each branch of the
circuit is the algebraic sum of the independently determined currents:

A Superposition theorem
B Fleming's left-hand rule
C Norton's theorem
D Right-hand grip rule
E Thevenin's theorem

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1.1.9 If a solenoid is gripped in the right hand with the fingers pointing in the direction of the
current flow, the outstretched thumb, if held in parallel to the axis of the solenoid, will
point to the north end of the solenoid:

A Superposition theorem
B Fleming's left-hand rule
C Norton's theorem
D Right-hand grip rule
E Thevenin's theorem

1.1.10 If the thumb, index finger and middle finger are held at right angles to each other, with
the index finger pointing in the direction of the flux and the middle finger in the direction
of the current, the thumb will indicate the direction of the force:

A Superposition theorem
B Fleming's left-hand rule
C Norton's theorem
D Right-hand grip rule
E Thevenin's theorem
(10 × 1) (10)

1.2 A heater of 40 W, which draws 2 A, and a resistor of 20 Ω are connected in

parallel. A resistor of unknown value is connected in series with the parallel
branch.
Calculate the value of the unknown resistor if the circuit is connected across a DC
supply of 32 V. (6)

1.3 Temperature coefficient of resistance is defined as the increase in unit resistance

of a substance per unit rise in temperature from 0 °C to the applied voltage, and is
inversely proportional to the resistance of the circuit.

1.3.1 Name TWO materials that have a positive temperature coefficient

of resistance.
1.3.2 Name TWO materials that have a negative temperature coefficient
of resistance.
(2 × 2)(4)

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1.4 An electrical network has two or more voltage sources

Apply Kirchhoff's laws and determine the magnitude of the current flowing in each branch of the
circuit in FIGURE 1 above:

1.4.1 𝐼1 (6)

1.4.2 𝐼2 (2)

1.4.3 𝐼3 (2)

[30]

QUESTION 2: AC THEORY

3.1 Explain the effective value of an alternating current. (2)

3.2 A circuit consist of coil A (36 Ω resistor and an inductance of 200 mH) connected in
parallel with (30 Ω resistor in series with a capacitance of 55 μF). The combination
is then connected in series with coil B (20 Ω resistor and an inductance of 100 mH).
The circuit is supplied by 200 V/50 Hz.

Determine the following:

3.2.1 The total current drawn by the circuit (12)

3.2.2 The voltage drop across the two coils (4)
3.2.3 The current through each branch of the parallel circuit (2)
[20]

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QUESTION 3: DC MACHINES

3.1 An eight-pole, lap-connected armature, driven at 450 r/min, is required to generate 250
V. The useful flux per pole is 0,05 Wb. The armature has 120 slots. Calculate a suitable
number of conductors per slot. (5)

3.2 Briefly explain the following methods of self-excited field coil connections:

3.2.1 Shunt-connected

3.2.2 Series-connected

3.2.3 Compound-connected
(3 × 2) (6)

[11]

TOTAL 61

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