Electrical Technology Paper 1 (English)

Feb-March 2012 — Grade 12 / Matric — Electrical Technology

Past Paper 2012 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 12 pages 📝 100 items found ∑ 2 math symbols 📚 2 topics

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Questions — A Preview of What to Expect in the Document

100

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Q1— Section header —

1.1Describe why it is neit her ethical nor legal to expect a person to work on

1.2When an entrepreneur wishes to promot e a new product, he must firstly do market research. Give TWO reasons why, and describe why they are

1.3Global warming is creating a environment. List THREE suitable ener gy sources that have little negative

Q2— Section header —

2.1With reference to the design problem in your PAT project, name THREE of must be followed. (3\

2.2Give THREE reasons why it is important to follow th e technological process in the completion of an artefact/project. (3\

2.3The design of the circuit board used in your PAT is important. Describe, giving TWO reasons why this is important. (4\

Q3— Section header —

3.1State why it is dangerous to use water trical fire. (2\

3.2Explain why it is important to have t he correct level of light ing in an electrical technology workshop. (2\

3.3Name TWO ways in which HIV/Aids can be transmitted between humans. (2\

3.4Describe how an earth-leakage unit can pr when using a faulty electrical appliance. (2\

3.5Name ONE essential pi ece of safety equipment that must be used when working with a grinding machine. (1\

3.6Give ONE reason why it is important to maintain tools in a good condition. (1\ NSC

Q4— Section header —

4.1Name TWO advantages of a thr ee-phase system in single-phase system.

4.2Power distribution to all consumers is done in the star connection. Explain

4.3A three-phase balanced load is connected in delt a across a 380 V supply. The load current is 5 A with = 5 A = 0,9

4.3.1The current in each phase of the load (3\

4.3.2The total power dissipated by the load (3\

Q5— Section header —

5.1What will happen to t he brightness of an incande scent lamp, connected in

5.2Name ONE disadvantage of a poor power factor. (1\

5.3A capacitor with a c apacitive reactance of 250 , an inductor with an inductive reactance of 300 and a resistor with a resistance of 500 are all f = 50 Hz

5.3.1Draw a labelled circuit diagram. (4\

5.3.2Calculate the total impedance of the circuit. (3\

5.3.3Calculate the power factor of the circuit and state whether it is NSC

5.4Refer to the circuit in FIGURE 5.1. FIGURE 5.1: RLC SERIES CIRCUIT f = 50 Hz Calculate the following:

5.4.1The supply voltage (3\

5.4.2The inductive reactance of the inductor (3\

5.4.3The capacitive react ance the capacitor (3\

5.4.4The capacitance of the capacitor (3\

5.4.5Draw the phasor diagram of th e circuit. Indicate the direction of R L C 120 V 85 V 122,84 V I = 5 A NSC

Q6— Section header —

6.1Draw a fully labelled symbol of an SCR. (3\

6.2Describe ONE method to switch an SCR on. (3\

6.3The diagram in FIGURE 6.1 is the characteristic curve of an SCR. With STIC CURVE OF AN SCR

6.3.1Explain what occurs at reverse breakdown voltage. (3\

6.3.2When the SCR is conducting (refe r to FIGURE 6.1\

6.3.3When the SCR is conducting, de scribe what determines the current

6.3.4If the current flowing through the SCR drops below I , what will NSC 220 V/50 Hz supply.

6.4The lamp-dimming circuit in FIGURE 6.2 is connected to a

6.4.1Name the components marked . (2\

6.4.2If the value of R is decreased, the brig htness of the lamp will increase. Explain how this occurs.

6.4.3Explain the function of R . (2\

6.5Name ONE advantage of THYRISTOR control when compared to RESISTOR Rload NSC

Q7— Section header —

7.1Redraw and complete the table in FIGURE 7.1 in your ANSWER BOOK. > V OUT < V OUT = V OUT FIGURE 7.1: OP-AMP

7.2Draw a non-inverting voltage comparator using an op-amp.

7.3Describe the working pr inciple of an op-amp. (3\ + - V2 V1 VOUT NSC IN

7.4Answer the following questions wi th reference to FIGURE 7.2.

7.4.1Name the circuit above. (1\

7.4.2With the given in put signal, draw the output signal and the input

7.4.3Describe what will occur to the feedback if the value of R is increased.

7.4.4Explain the function of R (2\

7.4.5What is common to both the input and output? (1\

7.5State whether an op-amp is a volt age or a current amplifier. (1\

7.6Describe the following terms with refer ence to the characteristics of an ideal

7.6.1Unconditional stability (2\

7.6.2Differential inputs, in other words two inputs (2\

Q8— Section header —

8.1Name ONE type of loss in a transformer. (1\

8.2When transmitting power over a long di up transformer is connected to the high -tension conductors. Is the secondary

8.3Explain why the core of a transformer is made of laminated plates and not of NSC is connected to an 8 kV supply.

8.4A star-star-connected transformer has 800 turns per phase on its primary windings and 60 turns per phase on its secondary windings. The transformer

8.4.1The primary phase voltage (3\

8.4.2The secondary phase voltage (3\

8.5A step-up transformer can step up voltage from a low value to a very high

Q9— Section header —

9.1Give TWO examples of the fo llowing with reference to PLCs:

9.1.1Inputs (2\

9.1.2Outputs (2\

9.2Name the following la dder diagram symbols:

9.2.1NSC

9.3.1Name the logic gate that FIGURE 9.1 represents. (1\

9.3.2Draw the logic symbol of the gate. (2\

9.3.3Draw a circuit diagram using two switches and a lamp that

9.4The following operands are used in the programming of PLCs. Give TWO

9.4.1Timing devices (3\

9.4.2Counting devices (3\

9.5Draw the relay control circuit of t he ladder logic diagram in FIGURE 9.2 in

9.6With reference to relay control:

9.6.1Explain why a PLC is more economical. (2\

9.6.2Explain why a PLC has quicker delivery. (2\

9.6.3Explain why a PLC requires less maintenance. (2\

9.7Describe what PLCs are used fo r and give ONE example. (3\ NSC cient and has a power factor of 0,8

Q10— Section header —

10.1Name ONE method of cooling th ree-phase induction motors. (1\

10.2A three-phase delta-connected induction mo tor draws a current of 20 A from a 380 V/50 Hz supply. The motor is 100% effi = 20 A f = 50 Hz Calculate:

10.2.1The output power of the motor (3\

10.2.2The apparent power of the motor (3\

10.2.3The phase current of the motor (3\

10.3Give THREE possible electrical r easons why a three-phase induction motor

10.4Describe ONE electrical inspection that must be done before installing a

10.5Name THREE losses that occur in three-phase induction motors. (3\

10.6Describe the basic principle of operati on of a three-phase induction motor. (7\

10.7Describe the function of a no-volt co il in a three-phase motor starter. (2\

10.8Describe why interlocking contacts are necessary in a three-phase star-delta motor starter.

10.9State how the rotation of a three-phase motor can be reversed. (1\ FL

Mathematical Content

f(x)trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections10 + 10 + 10 + 10 + 30 + 25 + 25 + 15 + 35 + 30 = 200 marks

Per-question sum77 marks

Paper information

SubjectElectrical Technology

Year2012

SessionFeb-March

TypePast Paper

PaperPaper 1

LanguageEnglish

Pages14

Downloads5

Examination context

Decade2010s

Years ago14y

Season—

Start day—

Exam period—

Days since exam—

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