ELEC TECH QP SEPT2023_Electronics_English_hlayiso.com_.pdf

NATIONAL SENIOR CERTIFICATE GRADE 12 SEPTEMBER 2023 ELECTRICAL TECHNOLOGY: ELECTRONICS MARKS: 200 TIME: 3 hours This question paper consists of 22 pages, including a 2-page formula sheet.

2 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) INSTRUCTIONS AND INFORMATION 1. This question paper consists of SIX questions. 2. Sketches and diagrams must be large, neat and fully labelled. 3. Show ALL calculations and round off answer correctly to TWO decimal places. 4. Number the answers correctly according to the numbering system used in this question paper. 5. You may use a non-programmable calculator. 6. Show the units for ALL answers of calculations. 7. A formula sheet is provided at the end of this question paper. 8. Write neatly and legible. Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 3 QUESTION 1: MULTIPLE-CHOICE QUESTIONS Various options are given as possible answers to the following questions. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.15) in the ANSWER BOOK, for example 1.16 D. 1.1. An attempt to numerically determine the probabilities of various adverse events and the likely extent of the losses if the event occurs is known as … A risk analysis. B quantitative risk analysis. C qualitative risk analysis. D dangerous practices. (1) 1.2 During resonance in a series RLC circuit … A Z = R. B Z < R. C Z > R. D Z is maximum. (1) 1.3 When increasing the frequency of a RLC circuit, the resistance will … A also increase. B decrease. C remain the same. D double its value. (1) 1.4 The power expended in a purely inductive or capacitive circuit is known as the … power. A real B true C reactive D apparent (1) 1.5 A bipolar junction transistor (BJT) is regarded as a(n) … device. A current controlled B drain-current (ID) C voltage-controlled D insulated-gate type (IGBT) (1) 1.6 The advantage of a field-effect transistor over a bipolar transistor is that it has a(n) … A low amplification factor. B high input current. C extremely low input resistance. D extremely high input resistance. (1) Copyright reserved Please turn over

4 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 1.7 The N-channel JFET will operate correctly when the … A gate-to-source pn-junction is forward biased. B gate-to-source pn-junction is reversed biased. C drain is connected to ground. D gate is connected to the source. (1) 1.8 To which input terminal of a 741-operational amplifier would a signal be connected if the output signal is in phase with the input signal? A Terminal 2 B Terminal 3 C Terminal 1 D Terminal 4 (1) 1.9 When a square wave is applied to the input of an op-amp integrator circuit, the output will be a … A sine waveform. B constant DC voltage. C triangular waveform. D square waveform. (1) 1.10 A(n) … is a specialised op-amp circuit that compares two input voltages and produces an output that is always at either one of the two states. A integrator B differentiator C comparator D Schmitt trigger (1) 1.11 When the input voltage to a non-inverting Schmitt trigger is smaller than the reference voltage, the output is driven into … A positive saturation. B negative saturation. C both negative and positive saturation. D zero saturation. (1) 1.12 The frequency response range that occurs between the lower and upper frequencies in the frequency response curve of amplifiers is called … A midrange frequency. B critical frequency. C distortion. D decibel. (1) Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 5 1.13 Correct biasing method for a transistor amplifier requires the base-emitter junction to be … biased. A reverse biased and the collector-base junction is forward B forward biased and the collector-base junction is reverse C reverse biased and collector-base junction is reverse D forward biased and the collector-base junction is forward (1) 1.14 The RF amplifier will amplify … A a single band of frequencies. B all frequencies. C DC signals. D All of the above. (1) 1.15 Coupling capacitors … A let through AC signals but block DC. B let through DC signals but block AC. C let through AC and DC signals. D block AC and DC signals. (1) [15] Copyright reserved Please turn over

6 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) QUESTION 2: OCCUPATIONAL HEALTH AND SAFETY (GENERIC) 2.1 State TWO factors needed to ensure a strong work ethic in a company. (2) 2.2 Define a critical incident in a workshop. (2) 2.3 Name ONE safety precaution you would observe when handling concentrated chemicals in a Printed Circuit Board (PCB) workstation. (1) 2.4 Differentiate between an unsafe act and a calculated risk in a workshop. (2) 2.5 Explain why you must protect yourself when helping a person who is being shocked by electricity. (1) 2.6 Explain why a person should not interfere with, or misuse, equipment in the workshop that is provided for health and safety. (2) [10] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 7 QUESTION 3: RLC CIRCUITS (GENERIC) 3.1 Define inductive reactance with reference to RLC circuits. (2) 3.2 Draw a full, labelled cycle of the waveforms representing the phasor diagram in FIGURE 3.2. VL X-Axis X-Axis I FIGURE 3.2: VOLTAGE AND CURRENT PHASOR DIAGRAM (3) 3.3 A series RLC circuit has a resistor of unknown value, a capacitor with a capacitance of 200 ɥF and an inductor with a reactance of 31,55 Ω connected to a 110 V/60 HZ AC supply. The impedance of the circuit is 101,65 Ω. Given: C = 200 ɥF XL = 31,55 Ω VS = 110 V f = 60 Hz Z = 101,65 Ω Calculate: 3.3.1 The capacitive reactance (3) 3.3.2 The current flowing through the circuit (3) 3.3.3 The value of the resistor in the circuit (3) 3.3.4 The inductance of the inductor (3) 3.4 A coil with a negligible resistance has an inductance of 50 mH and is connected in series with a 60 ɥF capacitor and a 100 Ω resistor. The circuit is connected to a 220 V supply with a variable frequency. Calculate the resonant frequency of the circuit. (3) Given: L = 50 mH C = 60 ɥF VS = 220 V Copyright reserved Please turn over

8 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 3.5 Refer to FIGURE 3.5 below and answer the questions that follow. IL = 4,54 A Xc = 11,83Ω Vs = 100 V/25 Hz IR = 9,09 A FIGURE 3.5: PARALLEL RLC CIRCUIT Given: IR = 9,09 A IL = 4,54 A XC = 11,83 Ω VS = 100 V f = 25 Hz Calculate: 3.5.1 The current flowing through the capacitor (3) 3.5.2 The total current flowing through the circuit (3) 3.5.3 The power factor (3) 3.5.4 State, with a reason, whether the current is leading or lagging the voltage (2) 3.6 Define selectivity of a resonant circuit. (2) 3.7 Name TWO factors that determine the quality factor(Q) of a resonant circuit. (2) [35] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 9 QUESTION 4: SEMICONDUCTOR DEVICES (SPECIFIC) 4.1 Draw a neatly labelled symbol of an N-channel JFET. (3) 4.2 FIGURE 4.2 below shows a cross-section of the construction of an enhancement mode MOSFET. Answer the questions that follow. A B C Silicon- insulation D P- substrate FIGURE 4.2: ENHANCEMENT MODE MOSFET 4.2.1 Label A, B, C and D. (4) 4.2.2 Indicate whether the enhanced channel consists of P-type or N-type material. (1) 4.3 Refer to the UJT and explain the term cut off. (4) 4.4 Draw a fully labelled circuit diagram of the Darlington pair. (5) Copyright reserved Please turn over

10 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 4.5 Refer to FIGURE 4.5 of an ideal op-amp below and answer the questions that follow. FIGURE 4.5: OP-AMP 4.5.1 Label points A, B and C. (3) 4.5.2 Explain what makes the op-amp ideal to amplify alternating voltages. (2) 4.6 Refer to FIGURE 4.6 below and answer the questions that follow. FIGURE 4.6: OP-AMP 4.6.1 Identify the above circuit diagram. (1) 4.6.2 Calculate the value of feedback resistor RF. (3) 4.7 Explain how a 100 mV sine wave signal would react if the gain of the circuit is 10 and the signal is connected to the ... 4.7.1 inverting input of the component. (3) 4.7.2 non-inverting input of the component. (3) 4.8 Describe the advantages of using negative feedback in an op-amp. (4) Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 11 4.9 Refer to FIGURE 4.9 below and answer the questions that follow. Ground 1 8 2 7 555 3 6 Threshold 4 5 FIGURE 4.9 4.9.1 Label pins 2, 3, 5 and 8. (4) 4.9.2 Explain the function of pin 6. (3) 4.9.3 State the supply voltage range at which the 555 IC operates. (2) [45] Copyright reserved Please turn over

12 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) QUESTION 5: SWITCHING CIRCUITS 5.1 Name the type of the multivibrator that: 5.1.1 Produces one pulse cycle of ‘high’ and low’ when a trigger pulse is applied (1) 5.1.2 Changes state when a trigger pulse is applied and remains in that state (1) 5.2 Draw a circuit diagram of an astable multivibrator. (5) 5.3 Refer to the circuit in FIGURE 5.3 below and answer the questions that follow. +6V R1 R2 10 kΩ 10 kΩ R3 4 8 630 Ω 7 555 3 6 2 1 5 S1 S2 Set Reset LED C2 10 nF FIGURE 5.3: MULTIVIBRATOR 5.3.1 Identify the above multivibrator. (2) 5.3.2 State the function of R1 and R2 . (2) 5.3.3 Describe what happens when the set switch, S1 , is pressed. (3) 5.3.4 Explain why threshold pin 6 is connected directly to ground. (3) Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 13 5.4 Refer to FIGURE 5.4 below and answer the questions that follow. Upper trigger level Input V t Lower trigger level +VCC Output V t - VCC FIGURE 5.4: SCHMITT TRIGGER INPUT AND OUTPUT 5.4.1 State whether the output signal represents an inverting or a non- inverting Schmitt trigger. Motivate your answer. (3) 5.4.2 Draw the circuit diagram of the Schmitt trigger consisting of two resistors and a 741 op-amp that will produce the output signal in FIGURE 5.4. (7) Copyright reserved Please turn over

14 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 5.5 Refer to FIGURE 5.5 below and answer the questions that follow. FIGURE 5.5: INVERTING SUMMING AMPLIFIER Given: 𝑉𝑉1 = 200 mV 𝑉𝑉2 = 300 mV 𝑉𝑉3 = 400 mV RF = 100 kΩ 𝑅𝑅1 = 20 kΩ 𝑅𝑅2 = 10 kΩ 𝑅𝑅3 = 25 kΩ 5.5.1 Describe how the gain of this amplifier can be determined. (3) 5.5.2 Calculate the output voltage of the amplifier. (4) 5.5.3 Calculate the gain of the amplifier using voltage values. (3) 5.5.4 Explain the advantage of using a variable resistor in the feedback loop instead of a fixed resistor. (2) 5.5.5 What will happen to the output voltage if the value of R2 is changed to 5 kΩ? (2) 5.6 Draw a circuit diagram of an op-amp integrator with input and output signals. (6) 5.7 Name THREE key operating points of the op-amp integrator circuit. (3) [50] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 15 QUESTION 6: AMPLIFIERS 6.1 Refer to FIGURE 6.1 below and answer the questions that follow. FIGURE 6.1: BIASED NPN TRANSISTOR 6.1.1 Determine Vce for the circuit when it is at rest. (1) 6.1.2 Calculate the maximum collector current that can flow in the circuit. (3) Copyright reserved Please turn over

16 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 6.2 Refer to FIGURE 6.2 below and answer the questions that follow. + 9 VCC R1 RC 400 Ω C2 10 kΩ 10 µF C1 1 µF T1 ß 200 = VCE VIN 2, 38 V 2 mV( AC) CE R2 RE 100 µF 1,5 kΩ 1 kΩ 0 V FIGURE 6.2: AMPLIFIER CIRCUIT DIAGRAM 6.2.1 Identify the amplifier in FIGURE 6.2. (1) 6.2.2 Describe the biasing method for Class A amplification. (4) 6.2.3 Determine the voltage drop across Rc . (3) Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 17 6.3 Refer to FIGURE 6.3 below and answer the questions that follow. +VCC RB1 T1 T2 Q1 Output signal Q2 RB2 RE 0V FIGURE 6.3: AMPLIFIER CIRCUIT DIAGRAM 6.3.1 Identify the amplifier circuit in FIGURE 6.3. (1) 6.3.2 Name the type of transistor used in the circuit. (1) 6.4 A push-pull amplifier circuit has the following information: Given: Input power = 750 mW Output power = 28 W Input voltage = 230 V Output voltage = 219 V Input current = 3,6 mA Output current = 15,3 mA Output impedance = 40 Ω Calculate the following: 6.4.1 Current gain in dB (3) 6.4.2 Voltage gain in dB (3) 6.4.3 Power gain in dB (3) Copyright reserved Please turn over

18 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 6.5 Draw a circuit diagram of a complementary push-pull pair amplifier. (5) 6.6 Refer to FIGURE 6.6 below of a radio-frequency amplifier. FIGURE 6.6: RADIO-FREQUENCY AMPLIFIER Draw a fully labelled frequency response curve of the RF-coupled amplifier. (4) Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 19 6.7 Refer to FIGURE 6.7 below of an RC-phase shift oscillator using FET and answer the questions that follow. +VCC RB RC C5 C1 C2 C3 Q1 VOUT R1 R2 R3 R4 C4 FIGURE 6.7: RC-PHASE SHIFT OSCILLATOR 6.7.1 Define the term oscillator. (2) 6.7.2 Describe how the RC-phase shift oscillator achieves its phase shift of 360° during its operation. (4) Copyright reserved Please turn over

20 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) 6.8 Refer to FIGURE 6.8 below and answer the questions that follow. + Vcc L3 R1 C1 COUT C2 Q1 L1 C3 VOUT L2 R2 RE CE 0V FIGURE 6.8: OSCILLATOR CIRCUIT DIAGRAM 6.8.1 Identify the oscillator in FIGURE 6.8. (1) 6.8.2 Discuss how oscillation is achieved in this circuit. (6) [45] TOTAL: 200 Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: ELECTRONICS 21 FORMULA SHEET RLC CIRCUIT SEMI-CONDUCTORS DEVICES 1 𝐴𝐴𝑉𝑉 = 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 = 𝑅𝑅𝐹𝐹 𝑋𝑋𝑋𝑋 = 2𝜋𝜋𝜋𝜋𝜋𝜋 𝑎𝑎𝑎𝑎𝑎𝑎 𝑋𝑋𝑋𝑋 = 𝑉𝑉𝑉𝑉𝑉𝑉 𝑅𝑅𝐼𝐼𝐼𝐼 2𝜋𝜋𝜋𝜋𝜋𝜋 𝑅𝑅𝐹𝐹 𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 =𝑉𝑉𝐼𝐼𝐼𝐼 = (− ) SERIES 𝑅𝑅𝐼𝐼𝐼𝐼 𝑅𝑅 𝐴𝐴𝑉𝑉 =1+ 𝐹𝐹 𝐼𝐼𝑇𝑇 =𝐼𝐼𝑅𝑅 =𝐼𝐼𝐶𝐶 = 𝐼𝐼𝐿𝐿 𝑅𝑅𝐼𝐼𝐼𝐼 𝑅𝑅𝐹𝐹 𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 = 𝑉𝑉𝐼𝐼𝐼𝐼 (1 + ) 𝑍𝑍 = �𝑅𝑅2 + (𝑋𝑋𝐿𝐿 − 𝑋𝑋𝐶𝐶 )2 𝑅𝑅𝐼𝐼𝐼𝐼 𝛽𝛽𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 =𝛽𝛽1 × 𝛽𝛽2 𝑉𝑉𝑉𝑉 = �𝑉𝑉𝑅𝑅 2 + (𝑉𝑉𝐿𝐿− 𝑉𝑉𝐶𝐶 )2 AMPLIFIERS 𝑉𝑉𝑉𝑉 = 𝐼𝐼𝑋𝑋𝐿𝐿 and 𝑉𝑉𝑉𝑉 = 𝐼𝐼𝑋𝑋𝐶𝐶 and 𝑉𝑉𝑇𝑇 = 𝐼𝐼𝐼𝐼 𝑉𝑉𝐶𝐶𝐶𝐶 = 𝑉𝑉𝐶𝐶𝐶𝐶 𝑉𝑉𝐶𝐶𝐶𝐶 𝑅𝑅 𝐼𝐼𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 = 𝑅𝑅𝐶𝐶 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 = 𝑍𝑍 𝐴𝐴 𝐴𝐴′ = 𝑉𝑉𝑅𝑅 1+𝛽𝛽𝛽𝛽 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 = 𝑉𝑉𝑇𝑇 𝑃𝑃𝑜𝑜𝑜𝑜𝑜𝑜 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝐴𝐴𝑃𝑃 = 𝑙𝑙𝑙𝑙𝑙𝑙10 � � 𝑃𝑃𝑖𝑖𝑖𝑖 𝑋𝑋𝐿𝐿 𝑋𝑋𝐶𝐶 𝑉𝑉 𝑉𝑉𝐶𝐶 1 𝐿𝐿 𝑄𝑄 = = = 𝐿𝐿 = = � 𝐸𝐸 𝑍𝑍 𝑍𝑍 𝑉𝑉𝑆𝑆 𝑉𝑉𝑆𝑆 𝑅𝑅 𝐶𝐶 𝐴𝐴𝑉𝑉 = 20 𝑙𝑙𝑙𝑙𝑙𝑙10 𝑜𝑜𝑜𝑜𝑜𝑜 dB 𝐸𝐸𝑖𝑖𝑖𝑖 𝐼𝐼 PARALLEL 𝐴𝐴𝐼𝐼 = 20 𝑙𝑙𝑙𝑙𝑙𝑙10 𝑜𝑜𝑜𝑜𝑜𝑜 𝐼𝐼𝑖𝑖𝑖𝑖 1. 𝑉𝑉𝑉𝑉 = 𝑉𝑉𝑅𝑅 =𝑉𝑉𝐿𝐿 = 𝑉𝑉𝐶𝐶 𝐹𝐹0 = 1 2𝜋𝜋�𝐿𝐿𝑇𝑇 𝐶𝐶 𝑽𝑽 𝑉𝑉 𝑉𝑉 2. 𝐼𝐼𝑹𝑹 = = 𝑎𝑎𝑎𝑎𝑎𝑎 𝐼𝐼𝐿𝐿 = = 𝐼𝐼𝐶𝐶 = Fr = 1 𝑹𝑹 𝑋𝑋𝐿𝐿 𝑋𝑋𝐶𝐶 2𝜋𝜋√𝐿𝐿𝐿𝐿 1 𝐹𝐹𝑂𝑂 = 2𝜋𝜋√6 𝑅𝑅𝑅𝑅 3. 𝐼𝐼𝑇𝑇 = �𝐼𝐼𝑅𝑅 2 + (𝐼𝐼𝐿𝐿 − 𝐼𝐼𝐶𝐶 )2 𝐼𝐼 4. 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 = 𝑅𝑅 𝐼𝐼𝑇𝑇 𝑋𝑋𝐿𝐿 𝑋𝑋𝐶𝐶 𝑉𝑉𝐿𝐿 1 𝐿𝐿 5. 𝑄𝑄 = = = = =� 𝑍𝑍 𝑍𝑍 𝑉𝑉𝑆𝑆 𝑅𝑅 𝐶𝐶 Copyright reserved Please turn over

22 ELECTRICAL TECHNOLOGY: ELECTRONICS (EC/SEPTEMBER 2023) SWITCHING CIRCUITS 𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 𝑅𝑅𝑓𝑓 1. Gain A𝑉𝑉 = = −� � inverting operational amplifier 𝑉𝑉𝐼𝐼𝐼𝐼 𝑅𝑅𝑖𝑖𝑖𝑖 𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 𝑅𝑅𝑓𝑓 2. Gain A𝑉𝑉 = =1+� � non-inverting operational amplifier 𝑉𝑉𝐼𝐼𝐼𝐼 𝑅𝑅𝑖𝑖𝑖𝑖 𝑅𝑅𝑓𝑓 3. 𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 = 𝑉𝑉𝐼𝐼𝐼𝐼 × �− � inverting amplifier 𝑅𝑅𝑖𝑖𝑖𝑖 4. 𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 = −(𝑉𝑉1 + 𝑉𝑉2 + 𝑉𝑉3 ) summing up op-amp 1 5. 𝑓𝑓𝑟𝑟 = 2𝜋𝜋√𝐿𝐿𝐿𝐿 1 6. 𝑓𝑓 = 2𝜋𝜋√6𝑅𝑅𝑅𝑅 Copyright reserved Please turn over