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NATIONALSENIOR CERTIFICATEGRADE 12SEPTEMBER 2018ELECTRICAL TECHNOLOGYELECTRONICSMARKS:200TIME:3 hoursThis question paper consists of 11 pages, including a 1-page formula sheet.INSTRUCTIONS AND INFORMATION1.This question paper consists of FIVE questions.2.Sketches and diagrams must be large, neat and fully labelled.3.Show ALL calculations and round off answers correctly to TWO decimal places. Show the units for ALL answers of calculations.4.Number the answers correctly according to the numbering system used in this question paper.5.You may use a non-programmable calculator.6.A formula sheet is provided at the end of this question paper.7.Write neatly and legible.QUESTION 1: OCCUPATIONAL HEALTH AND SAFETY1.1Summarise the purpose of the Occupational Health and Safety Act. (2)1.2Explain the ‘let-go’ current during an electrical shock.(2)1.3State ONE unsafe condition that must be avoided in a workshop.(1)1.4Give ONE unsafe act in a school workshop that can cause an accident.(1)1.5Describe TWO standard treatments for shock.(2)[8]QUESTION 2: RLC2.1A series RLC circuit consists of an inductor with an inductive reactance of24 ?, a resistor with a resistance of 12 ? and a capacitor with a capacitive reactance of 18 ? connected across a 30 V supply.FIGURE 2.1Calculate the:2.1.1Impedance of the circuit(3)2.1.2Current flowing through the circuit(3)2.1.3Voltage across each component in the circuit(6)2.1.4Prove by calculation that the sum of the three voltages equals the supply voltage.(3)2.1.5Circuit phase angle and state whether is it leading or lagging(3)2.1.6Draw a fully labelled voltage phasor diagram.(5)2.2The phasor diagram in FIGURE 2.2 indicates the current values flowing through the components of a parallel circuit connected across a 240 V/50 Hz supply. Refer to the diagram below and answer the questions that follow.FIGURE 2.2Calculate the:2.2.1Total current flow through the circuit(3)2.2.2Inductive reactance(3)2.2.3Inductance of the coil(3)2.3Define the following terms with reference to RLC circuits:2.3.1Resonance(2)2.3.2Q-factor in a parallel circuit(2)2.4A circuit with a resistor of 4 ?, an inductor with an inductive reactance of 157 ? and a variable capacitor set to 120 ?F are connected in series to a 100 V/50 Hz supply.Given:R = 4 ?XL = 157 ?Cvar = 120 ?FVs = 100 Vf = 50 HzCalculate the:2.4.1Value of the capacitance that will result in resonance at 50 Hz(3)2.4.2Q-factor of the circuit at resonance(3)[42]QUESTION 3: SEMICONDUCTORS3.1State whether a FET is a voltage or current controlled device.(1)3.2Sketch the circuit symbols for the following FETs:3.2.1N-channel JFET(3)3.2.2N-channel depletion MOSFET(3)3.3Explain the main advantage of a FET device over a bipolar junction transistor.(2)3.4Describe the difference between the inverting and non-inverting op-amp.(2)3.5Draw and label the operating characteristic for UJT by clearly labelling the cut-off, saturation and negative resistance regions.(3)3.6Sketch a labelled circuit symbol for an op-amp.(3)3.7Give THREE advantages of negative feedback.(3)3.8Refer to FIGURE 3.1 and answer the following question.FIGURE 3.13.8.1Identify the circuit diagram above.(1)3.9FIGURE 3.2 represents the non-inverting op-amp.FIGURE 3.2 NON-INVERTING OP-AMP3.9.1Determine the gain from the information given in FIGURE 3.2.(3)3.10Give any THREE modes of operation of a 555 timer IC.(3)3.11Sketch the pin layout of a 555 timer IC.(4)3.12Calculate the intrinsic stand-off ratio of a UJT if the internal resistance within the device is 2 k? for the upper resistance and 5 k? for the lower resistance.(3)[34]QUESTION 4: SWITCHING CIRCUITS4.1 List THREE types of multivibrators.(3)4.2Refer to FIGURE 4.1 and answer the questions which follow.FIGURE 4.14.2.1Identify the circuit diagram above.(1)4.2.2Describe the operation of the circuit diagram above.(4)4.3State TWO applications of a monostable multivibrator.(2)4.4Design the circuit diagram for a Schmitt trigger.(3)4.5Determine FOUR applications of a Schmitt trigger.(4)4.6Draw a fully labelled circuit diagram of a monostable multivibrator. Also include the input and output waveforms.(5)4.7Sketch a fully labelled circuit diagram for a 555 IC astable multivibrator circuit also showing input and output waveforms.(6)4.8Refer to FIGURE 4.2 which represents the summing amplifier. Calculate the circuit output voltage.(4)FIGURE 4.2: SUMMING AMPLIFIER4.9Refer to FIGURE 4.3 below to answer the question that follows.FIGURE 4.34.9.1Draw TWO full cycles of the input and output waveforms for this circuit if a sinusoidal waveform was added to its supply.(4)4.10FIGURE 4.4 represents a passive RC differentiator. Answer the question that follows.FIGURE 4.44.10.1Sketch the output wave form.(4)4.11Explain the operation of an integrator.(3)4.12Design a circuit diagram of an op-amp integrator.(4)4.13A 555 astable multivibrator circuit has the following components:Given:R1 = 47 k?C = 1 μFR2 = 5 k?Calculate the:4.13.1Charging time(3)4.13.2Discharging time(2)4.13.3Time to complete one cycle(3)4.13.4Frequency of oscillation(3)[58]QUESTION 5: AMPLIFIERS5.1What does the term amplifier mean?(2)5.2Refer to FIGURE 5.1 and calculate the maximum current and voltage across the transistor. Also draw the circuit load line.(8)FIGURE 5.15.3Draw a neat sketch of an input and output characteristic curve to show a common emitter connected transistor.(4)5.4State the biasing condition that must be met for a transistor to operate as an amplifier.(1)5.5Explain how Class B biasing is obtained.(2)5.6Design a block diagram showing negative feedback.(5)5.7Give THREE disadvantages of transformer coupling.(3)5.8Name THREE applications of an RC couple amplifier.(3)5.9Refer to the circuit below and answer the questions that follow.FIGURE 5.25.9.1Identify the circuit diagram above.(1)5.9.2State the chief function of the amplifier above.(1)5.9.3Briefly explain the operation of the circuit above.(3)5.10Explain the similarities and the differences in circuit components between the Colpitts and Hartley oscillator.(4)5.11A Colpitts oscillator operating at 10 kHz uses two capacitors C1 = 600 nF and C2 = 20 ?F. Calculate the value of the inductor in the resonant circuit.(5)5.12An RC phase shift oscillator uses identical variable capacitors each with a range of 100 pF to 500 Pf. The resistors are each 20 k?. Calculate the circuit frequency range of oscillation.(4)5.13Explain what comprises the feedback network in the following oscillator circuits:5.13.1A Hartley oscillator(1)5.13.2A Colpitts oscillator(1)5.13.3An RC-phase shift oscillator(1)5.14State THREE uses of an RF oscillator.(3)5.15Sketch and label the frequency response curve of an RC coupled amplifier.(6)[58]TOTAL:200FORMULA SHEETRLCXL=2πfLXC=12πfCZ= R2+(XL-XC)2Z= VTITP=VICosθPhase angle:Series circuit: Cosθ= RZParallel circuit:Cosθ= VRVZfR= 12πLCQ factor : Q= XLRQ= XCRBand Width= fRqSWITCHING CIRCUITVout= -(V1+ V2+ V3…..+Vn)Vout=-{V1×RFRin+ V2×RFRin+ V3× RFRin}f=1T = 1,44(R1+2R2)×C t1=0,693(R1+R2)×Ct2=0,693×R2×CT = t1+ t2f=1T=1,44(R1+2R2) ×C t1 =0.693( R1+R2) x Ct2 = 0.693 x R2 x CT= t1+ t2AMPLIFIERSVCE= VCCIC max= VCCRCAV= VoutVinfR= 12πLCCT=C1× C2C1+ C2fo= 12π6 RCfo= 12πLCSEMICONDUCTORVout= Vin(-RfRin) Vout= Vin(RfRin)5029200top00 ................
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