Electrical Technology English memo

November 2012 — Grade 12 / Matric — Electrical Technology

Memo 2012 Grade 12 English

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🎯 200 marks 📄 13 pages 📝 79 items found ∑ 1 math symbols 📚 3 topics

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2.5All calculations must show the formula (e\ Substitution of values must be done correctly. All answers

Q1— Section header —

1.1.1Coal causes air pollution which is harmful to the environment as man, anima l and plant life all rely on clean air for healthy living

1.1.2Availability of coal Economical (Any acceptable answer\ (2\

1.2Need to be a h ard worker Need to be a c reative thi nker. Must have sound financial management skills Good communication skills; Perso

1.3The cell phone has given many people more access to a wide range of communication methods which has allowed access to the business world. Education opportunities.

1.4Equal access to employment to scho ol leavers means that all learners leaving school should have had an education that does not disadvantage them in any way that gives them access to economic independence.

Q2— Section header —

2.1Investigation Designing Making Evaluati (4\

2.2To make the product according to the selected design and to improve the product after evaluation. (2\

2.3To identify possible improvements of the product. To collect data and information of the product. To conduct test on the prototype. To check if specifications are met. To see if the prototype is suitable before the final product is made.

Q3— Section header —

3.3Power to the circuit must be switched off when connecting meter leads. Make sure that the leads are connected to the correct terminal or sockets of the meter. Make sure that the multimeter is connected in series when measuring

3.4To prevent drowsiness which could cause loss of concentration resulting in an accident. To remove vapo r and smoke which are harmful to humans.

3.5To avoid electric shock. Some sections of the circuit may be live. The power supply could have been switched on by mistake. [10]10

Q4— Section header —

4.1ffective value or rms value

4.2Apparent power is the product of the supply voltage and the current in an AC system. = VI

4.3The active current is that component of current which is in phase with the supply voltage of an AC system. (3\

4.4[10]10

Q5— Section header —

5.1Capacitive reactance is the opposition to the flow of current a capacitor offers when the capacitor is connected across an alternating voltage supply.

5.2When the frequency of the supply is increased, the inductive reactance will increase thus increasing the impedance of the circuit . The increase in impedance will result in a decrease in current flowing through the circuit

5.3(3\ (3\

5.4.1(3\

5.4.2(3\

5.4.3(3\

5.4(3\

5.5If the capacitance of the capacitor is increase the capacitive reactance of the capacitor will decrease . The voltage across the capacitor will decrease which will result in an increase of the voltage across the resistor.

Q6— Section header —

6.1(2\

6.2.1The TRIAC may be used in the following applications Motor speed control Lamp dimming Temperature control Triacs are used in switching circuits. (Any ONE application\ (1\ tan

6.2.2ONE mark for correct symbol with no or incorrect labelling\ (3\

6.2At both points labelled gate pulse the TRIAC will be triggered into conduction if there is an appropriate voltage across the terminals of the TRIAC. (2\

6.2When the voltage across the TRIAC reaches V the TRIAC will begin to conduct without the gate being triggered.

6.2is the holding current of the TRIAC, this is the minimum current that must flow to keep the TRIAC conducting if the current through the TRIAC falls below I the TRIAC will switch off. (2\

6.2.6When the TRIAC begins to conduct the internal resistance of the TRIAC decreases therefore t he voltage across the TRIAC will decrease (2\

6.2.7It conducts in both directions. (1\

6.3Anode Cathode Gate

6.3acts as a current limiting resistor n the event that R is decreased to zero a short circuit is prevented. is increased the time constant of the trigger circuit is increased (t=RC\ This will prolong

Q7— Section header —

7.1.1Non nverting input Inverting input Output

7.1.2are the terminals to the dual DC supply that supplies power to the o amp. (2\

7.2The concept of feedback is to sample the voltage at the output terminal and to feed it back into one of the input terminals. (2\

7.4Non inverting op amp ONE mark showing phase and ONE

7.4.3The voltage gain of the circuit will decrease as R increases, because A is inversely proportional to R (ONE mark if only the

7.4.4The input and output waveforms will be in phase. The input and output amplitudes will be the same. (2\

7.5The frequency of the wave form remains unchanged (1\

7.6This will reduce the loading effect on the previous circuit. In so doing current will be drawn from that circuit herefore the voltage appearing at its output terminals will be passed on to the

Q8— Section header —

8.1Insufficient ventilation Short circuit Overloading Insufficient cooling substance (Any ONE (1\

8.2Electric circuit Magnetic circuit (2\

8.3To create a three phase four wire system so that a tran sformer can supply both single phase and three phase.

8.4.1(3\ 10

8.4.2(3\

8.4.3(3\ [15]15

Q9— Section header —

9.1.1This provides the power at a specific voltage to operate the PLC. (2\

9.1.2This is the device that is programmed externally to provide the necessary control of the plant (relays motors etc (2\

9.1.3These modules are the interface between the PLC and the plant equipment. (2\

9.2.1(4\

9.2.2(3\ 11000 240000 11000 11

9.3.1S Flip Flop atch Bistable multivibrator

9.3.2Set Reset (4\

9.3.3Memory device (1\

9.3.4(2\

9.4Simplified Economical Quick delivery Compact Changes to circuit design more easy to effect Improved reliability Reduced maintenance (Any THREE

Q10— Section header —

10.1By reversing the connections of any two of the three supply lines to the stator. (1\

10.2To check if the frame is earthed. To see if all electrical connections are fastened and insulated To verify if the correct voltage is used. (Any acceptable answer\ (2\

10.3Minimum of 0,5 . (Very h igh resistance\ (1\

10.4To limit the starting current of a squirrel cage motor at start.

10.5To protect electrical equipment from damage during faulty operating conditions and protecting the operator of the equipment.

10.6.1(3\

10.6.2cos cos (3\

10.6.3kVA kVA cos (3\

10.7It is important that a motor has a n information plate because the plate contains cruc ial information about the motor, for example Current rating Power factor

10.8The advantage of the three phase induction motor is that for the same size frame a three phase motor delivers more power It is also more efficient than a single phase motor as no additional starting circuit is required.

10.9.3Coil of contactor The motor will keep on operating but to maintain the same output power the current on the other two phases will increase. If the protection is set correctly it will engage,

Mathematical Content

trig

Topics Identified

CircuitsMachinesMaterials

Mark Allocation

Total200 marks

Sections10 + 10 + 10 + 30 + 25 + 25 + 15 + 35 = 160 marks

Paper information

SubjectElectrical Technology

Year2012

SessionNovember

TypeMemo

PaperSee title

LanguageEnglish

Pages13

Downloads1

Examination context

Decade2010s

Years ago14y

SeasonSpring (SH)

Start dayMonday

Exam periodNovember 2012

Days since exam5,101

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