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



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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;. /,' , o j >

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0013 66 /F 2001



- 3 -

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

- 5 -

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)

366 F 2001GO ON TO THE NEXT PAGE



10.

j~

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?

.

GO ON TO THE NE XT PAG E

00 1 366IF 2001



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

001366 1F 2001

Documents

Cxc Electricalpaper 2 - 2001