Electrical Technology - Digital Memo (English)

Exemplars 2018 — Grade 12 / Matric — Electrical Technology

Memo 2018 Grade 12 English

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🎯 200 marks 📄 13 pages 📝 94 items found 📚 2 topics

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2.1All calculations must show the formulae.

2.2Substitution of values must be done correctly.

2.3All answers MUST contain the correct unit to be considered.

2.4Alternative methods must be considered, provided that the correct answer is obtained.

2.5Where an incorrect answer could be carried over to the next step, the first answer will be deemed incorrect. However, should the incorrect answer be carried over correctly, the marker has to re calculate the values, using the incorrect answer from the first

2.6Markers should consider that candidates' answers may deviate slightly from the marking guidelines, depending on how and where in the calculation rounding off was used. 3. These marking guidelines are only a guide with model answers. Alternative

Q1— Section header —

1.1Workplace is any premises or place where a person performs work in the course of his employment. (2\

1.2To cooperate with employer or persons to ensure that any duty given by the employer to the employee shall be performed or compiled in accordance with requirements and procedures. To take reasonable care of health and safety for himself and other persons

1.3Dangerous fumes can accumulate in the workshop that can be inhaled by people making it an unsafe condition (2\

1.4To review the effectiveness of health and safety measures. To identify hazards and potential major incidents at the workplace. (2\

1.5Quantitative risk analysis is an attempt to numerically determine the probabilities of various adverse events and the likely extent of the losses if a particular event takes place. (2\ [10]10

Q2— Section header —

2.1.1The current and voltage are in phase and their phase angle is zero (2\

2.1.2

2.1.3

2.2.1(3\

2.2.2(3\

2.2.3(3\ 11,31 10 30 60

2.2.4(3\

2.2.5Power factor (3\

2.2.6The phase angle is leading (1\

2.3.1(a\ When the frequency of the supply increases, the inductive reactance (X L\ will increase because the supply frequency is directly proportional to the inductive reactance. (2\

2.3.2The resistance of a resistor is not affected by the increase or decrease of the frequency of the supply voltage (2\

2.3.3Z or Impedance (1\

2.4.1(3\

2.4.2(5\

2.4.3(3\ [40] 83 3,59 12040

1.5883,88Hz Fr Electrical Technology: Electronics DBE/2018 CAPS

Q3— Section header —

3.1The JFET is a voltage controlled device. (1\

3.2(3\

3.3If V GS is increased, the depletion layer between the N channel and the gate will widen. This widened depletion layer will make the

3.4MO SFET (metal oxide silicon field effect transistor\ (1\

3.5If V GS exceeds 0 V, the MOSFET operates in the enhancement mode. (1\

3.6The UJT can be used as a Switch Saw tooth generator (2\

3.7Darlington pair transistor. (3\

3.8.1Non inverting input Inverting input (2\

3.8.2It is important for the op amp to have a dual voltage supply to be able to amplify all signals above 0 and below 0

3.9.1(3\

3.9.2(3\

3.9.3the amplifier will increase to 90 and the output voltage will increase to 50 V.

3.10Timing functions (turning a light on and off for a prescribed time\ Creating a warning light Pulse, oscillation and signal generation Digital logic probes Controlling the positioning of a servo device

3.11Pin 6 (threshold\s the voltage at which the 555 IC will trigger. (2\ [30] 9,09 220 200030

Q4— Section header —

4.1(3\

4.2The bi stable multivibrator is defined as a circuit that is able to give and hold two stable output values, either high or low whenever a trigger pulse is received. (3\

4.3(3\

4.4.1Contact debouncer (1\

4.4.2is necessary to prevent pins 6 and 7 from being directly connected to the positive voltage supply when VR (3\

4.4.3An increase of C will increase the RC time constant of the circuit keeping the output at a high or

4.4.4When S1 is pressed, the input voltage on pin 2 will pulled down to 0 V. This triggers the 555 IC setting the output voltage at pin 3 and pin 7 to high. Once the capacitor voltage V C1 reaches 2/3 of the supply

4.5Radio receiver filters Contact de bouncer Analogue to digital converter Signal recovering (2\

4.6The Schmitt trigger is able to trigger at TWO different voltages. The moment the input rises above the upper trigger level its output will go to negative saturation and the moment the input falls below the lower trigger level its output

4.7(5\

4.8.1Resistor R determines the reference voltage of the comparator (1\

4.8.2Resistors R and R creates a voltage divider that feeds a reference voltage into the non inverting input

4.8.3To adjust the reference voltage the, resistor R can be replaced by a variable resistor (1\

4.9.1Inverting summing amplifier (2\

4.9.2Negative feedback (1\

4.9.3The gain of the amplifier is determined by the ratio of the feedback resistor to the input resistance of each branch. (3\

4.9.4(3\

4.10The function of a differentiator is to change a square wave into a triangular wave. (2\

4.11.1(3\

4.11.2A long time constant will cause the capacitor to discharge slower causing the output signal to become more like a distorted square wave. (2\

4.12.1Inverting integrator (2\

4.12.2(2\

4.12.3The higher the frequency for a particular time constant, the better the shape, but the smaller its amplitude. (2\ [60]60

Q5— Section header —

5.1Class B amplification is when the output collector current of the amplifier flows for only 180 of the input cycle. (2\

5.2.1when the transistor is OFF and collector current is not flowing When the transistor is biased, the collector current will flow (2\

5.2.2(3\

5.2.3(3\

5.2.4If the load resistance increases the value of the collector current decrease (1\

5.3If the supply voltage increases, collector current will increase and the quiescent point will move up the load line towards saturation (2\

5.4.1Is to enable each stage to individually maintain its own DC biasing levels without interference from any of its neighbouring stages. Allows the transfer of the alternating signal voltage between stages for

5.4.2(1\

5.4.3As the frequency rises the amplification will decrease due to parasitic capacitance which develop inside the transistor, their re ctances will become lower and would caus e upper frequency roll off.

5.5.1Poor frequency response Large and heavy Expensive components (2\

5.5.2If the loudspeaker is changed to a lower impedance loudspeaker, a matching transformer must be chosen to drive the speaker to ensure maximum power transfer. (3\

5.6.1When the dc base voltage drops to zero, transistors Q1 and Q2 are OFF. The input signal must pass through the region where both transistors are not conducting, this will cause cross over distortion. (2\

5.6.2(3\

5.6.3(6\

5.7.1adio frequency mplifier amplifies a single high frequency usually above 100 k

5.7.2Capacitor C and the primary turns of second transformer (T \forms the tuning circuit which resonate at the required frequency and passes the resonating frequency to the second LC tuned circuit formed by C

5.7.3By varying capacitors C1 and C2, the tuned circuit will resonate at different frequencies therefore passes a range of frequencies. (3\

5.8.1The RF coil offers resistance (reactance\against the change in the collector current and causes the collector voltage V to decrease. (2\

5.8.2The tank circuit receives energy from a dc source and convert that energy into a sinusoidal signal at a frequency determined by the inductor and capacitor. (2\

5.8.3(2\

5.8.4Hartley oscillator tank circuit consists of two inductors and one capacitor. Colpitts scillator tank circuit consists of

5.9.1The RC network will determine the frequency of oscillation and causes a phase shift of 180 (2\

5.9.2Positive feedback occurs when a portion of the output signal is fed back in phase with the input signal. (3\

5.9.3Phase shift around the feedback loop must be 0 degrees The voltage gain around the feedback loop must be 1 (2\

5.9.4The FET minimizes the loading effect when compared to the BJT due to its higher input impedance. This stabilizes the resonating frequency (2\ [60] TOTAL:60

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections10 + 40 + 30 + 60 + 60 = 200 marks

Paper information

SubjectElectrical Technology

Year2018

SessionExemplars

TypeMemo

PaperSee title

LanguageEnglish

Pages12

Downloads8

Examination context

Decade2010s

Years ago8y

Season—

Start day—

Exam period—

Days since exam—

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