cxc electricalpaper 2 - 2001
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TEST CODE 001366t : -FORM TP 2177 MA Y/JUNE 200 I
CARIBBEAN EXAMINAT IONS CO UNCIL
SECONDARY EDUCATION C ERTI FICATE
EXAMINA T IO NELECTRICAL TECHN OLOGY
Pape r 02 - Technic al P r oficien cy
2~hours
I. In addition to the 2t hours, candidates are allowed 10 minutes to read through the p~per . WritingMAY begin during the 10-minute period.
2. Al l working must be shown.
3. Use sketches where necessary to support your answers.
4. Silent electronic calculators may be used .
5. Candidates MUST answer NINE questions, ALL FIVE from SECTION A , THREE fromSECTION B and ONE from SECTION C .
r .
DO NOT TURN THIS PAGE UNTIL YOU A RE TOLD TO DO SO
Copyright © 2000 Caribbean Examinations Council . .All rights reserved.
366 F 200 I
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Candidates MUST answer NINE questions, ALL FIVE from Section A, THREE from Section Band ·
ONE from Section C.
SECTION A
Candidates MUST answer ALL FIVE questions in this section.Each question is worth EIGHT marks.
1 a) List FOUR properties of lines of magnetic flux. 4 marks)
b) In your answer booklet, sketch the magnetic field due to current in a straight conductor .Indicate the direction of the conventional current flow and the direction of the magneticfield. 4 marks)
2 a) Define the following terms:
i) Period
ii) Frequency
Hi) Cycle
iv) Instantaneous value , 4marks)
b) Explain what is meant by alternating voltage and current . 2niarks)
c) Give TWO reasons why alternating current is widely used for electrical power di s tribution . 2marks)
3. (1) a Define the following terms and give the symbol for EACH:
i) Power
ii) Energy 4marks)
b) Two lamps are rated to pass 0.2 A when connected across a 240 V supply in
i) parallel
ii) series.
Explain the difference in power output between i) and ii). 4marks)
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4 a) State TWO essential features of electrical analogue measuring instruments. 2marks)
b) List TWO factors which affect the sensitivity of moving coil instruments. 2 marks)
c) Figure 1 shows the internal connections of a measuring instrument . In your answer booklet,
writethenumberG ) and G and state the MAIN function of EACH of the corresponding
parts shown. 2marks)
0)
, Figure 1
d) Name the electrical quantity which can be measured by the instrument shown in Figure 1. 2marks)
5 a) State what is meant by the following terms:
i) Current rating
ii) Fusing factor 2 marks)
b) Give TWO reasons why it is necessary to use fuses and circuit breakers in electri cal circuitsand household equipment . 2marks)
c) Why is it important to earth the metal frame of electric motors? 2marks)
d) Name TWO tests carried out on a completed domestic installation before the supply isinitially connected. 2marks)
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SECTIONB
Candidates MUST answer THREE questions from this section.Each question is worth TWENTY marks.
6 a) State the fundamental conditions for logic gate operation. 2 marks)
b) For EACH of the FOUR basic logic gates
i) Write the name. 4 marks)
ii) Draw the logic symbol . 4 marks)
c) __The output of a logic gate is shown to be F = A + B + C. For the logic gate:
i)Draw the logic symbol . 2 marks)
ii) Write the truth table. 4 marks)
d) Sketch the logic network using a combination of gates to operate the functionF= A+ B . C 4 marks)
7
~~=== R, ,~fb Z -D
- 6D5 .
e ~¥.. . =-Ql ~ \+~r
10n 20n
~ ~I100V
Figure 2
Figure 2 shows a series parallel resistive circuit connected across a 100 V supply.
a) Calculate the total
i) resistance of the circuit
ii) current flowing through the circuit . 8 marks)
b) A pure inductance of 30 mH is connected in series with the circuit shown in Figure 2. Thenew circuit is connected to a 1 O O V 50Hz a.c. supply.
i) Sketch the new circuit .
ii) Calculate the total current flowing through the circuit . 12 marks)
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8 a) Define the following terms:
i) Resistivity
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ii) Temperature coeff icient of resis tance 4 marks)
b) A coil is wound from a 100m length of coppe r conductor h aving a cross -sectional area of1.0 mm?. . This coil operates initially at 2 0°C. Calcul ate the
i) resistance of the coil at 20 °C
ii) change in res istance of the coi l whe n it operates at a mean temperature o f 80 C. 1 6 marks)
[p = 1.59 x 10 -8 Qm at O °C; UO
= 0.00 428/deg C at 0 0 c] 9
r e Vcc 12 V
C1
· · ~ I ~ ~ · ~
F ig ur e 3
Figure 3 shows the circuit of a transistor a mplifier. The characteristic curves of thetran sistor used in Fig u re 3 are shown in F ig u re 4 on page 6.
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6
14 ~ I B = 1 6 0 ~ A
~ I 8 = 1 4 0 ~ A
10 ~ I B = 1 2 0 ~ A
~ ~ I 8 = 1 0 0 ~ A
6 ~ . I 8 = 8 0 ~ A
4 r I 8 = 6 o ~ A
2 ~ I 8 = 4 0 ~ A
o 3 62 5 7 8 9 10 11
V E V)----- --- ----- ---~
Figure 4
a) For the base current of I = 100 / .tA, and for the power supply V cc value of 12 V, indicatethe quiescent Q) point on the graph in Figure 4. Draw the load line on the graph.
4 marks)
b) Using the Q point on the graph in Figure 4, indicate the values of ICQ and V CQ
2marks)
c) Calculate the values of RB and RL shown in Figure 3. Assume V = 0.6 V. lOmarks)
d) State the fU ~ of the capacitors C and e2
and the resistor RB shown in Figure 3. 4 marks)
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10.
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7
SECT ION C
Candidates MUST answer ONE q uestio n f rom this section.Each question is worth TWENTY m ark s.
a) Sketch and label the schematic dra wing for EACH of the following d .c. motors:
i) Shunt wound
ii) Series wound
iii) Compound wound 12 marks)
b) On the sheet supplied , ske tch a nd label the spe ed char acteristics of shunt series andcompound wound motors to compl ete Figure 5. 6 marks
c) 2 markshat is the MAIN differen ce b etween a d .c. motor and a d .c. generator?
.
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11 .
8
a) Figure 6 shows a sketch of TWO types of transformer c onstruction. In your answer bookle t
write the numbers C D and and beside E ACH number write the name
b )
c )
Cd)
4 marks
In Figure 6 the numbers G the numb ers G and @
and @ refer t o the t ype of transform er construction. Write
in your an swer booklet and , beside EACH number, write
Draw a neat labelled scheI1 2.~ticsketch o f an auto transfo rmer .
EN D OF TEST
2 marks
2 marks
2 marks
Ce) State TWO advantages of an iron-cored transf ormer ove r an air-cored transfor mer . .. 4 marks
~ ~o -Ty pe tran sfo rm erconstr uct ion
o -Type tran sform ercon structi on
Cf)
Figure 6
of the corresponding part .
the name of the type of co nstruct ion.
Name TWO significant sources of powe r loss in a transfo rmer .
Write an expression for the efficiency of a t ransformer.
6 m ar ks
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