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ELECTRICITY (448)
Electricity Paper 1 (448/1)
30.18.2
1.
(OIl
CmmlTlONS FOk CQ:\lBlSTIO.\;
Fuel
Oxygen
Heat
(b)
TY PES OF EXTINGUISHERS
Carbon dioxide
Dry powder
Water
Any (.3 x '.,z)
Fo.un
2.
TY PES OF INSTITUTIONS
Technical Training Institute
Nationnl Polytechnics
InSli\utes ot technology
Youtn polytechnics
lb)
Any (4 x ~~)
DRY JOINT
(2 marks)
Occurs if solder W'·I~ not enough when joint was made.
3.
CAPACITORS
Air capacitor
Papa
Mica
Ele~:trolytk
Tantalum
(b)
(i)
AIl){4.,lh)
V, ;=: 200.\'416 =
sot!
v, == 200 - 80 = 120\/
Charge is the same on each capacitor.
=
(4x I)
Q = CV '" 6 x IO~ x $0 O.00048C
SECOND,\RY CELLS
Lead acid and alkaline.
(b)
Total EMF
= l .. 'iV
""-6' '" O,2Jl
T(J(al Internal resistance =
Total circuit resistance = R + r ." 10 +
5.
(a)
R
I'
o 2 :::: IO.2.Q
12
.
( 3, I)
RESlSTA:'\CE
(ii 54 .r 10
f1 .i. 5% :::: 540D ± 5<;i
(2
(b)
Average emf =
(fit == 0.5 x - 75 "" 37.~V
x 2)
(2,
547
n
6
.
(a)
[\1M;:\ETlC !;\"FLUX
form closed loop.
do not intersect.
they Me elastic.
lines of same polarity repel or vice versa.
(b)
Any (3 x I)
Deflecting device moves pointer OVer the instruments scale 10 enable qU3n!itiel'
W
be measured.
Controlling device .. allows the pointer to stop so that the scale tan be read. Abu
allows poi mer to return to zero.
Dumping device • prevents the pointer form oscillating to enhance steady value leading.
Any (3.x I)
(b)
LIGHT GALGE PVC COi\"DlIT
SHVCS
time (luring Installation.
no burrs left in conduit after tuning.
simplities routi ng conduit found corners .
. :\ail holes dose lip to avoid entry of moisture.
Less costly.
x.
( <1)
l-orward voltage is roughly double tha! of germanium diodes.
Canwi;!Jslijnd higher reverse voltage.
ell) operate al temperatures upto 15(f -20(t' compared to "iY' " l)U't.
Any (2 x I)
(b)
9.
.~··Y()k
c
(a)
(\rmatllf'C
Sketching .') parts x 0 "" 2%
(i)
overload or low supply
(it)
faulty !ht!nnoSJafl
falilty or loose starter or
tow voltage or aged lamp
(iiif
(i v)
548
10,
r'
I
~-
I
1-_.--._-_ .. ··..•..
..-- ____ . __
Correct projection
Elevations: FE
EE
Plan
Correct proportion
11/:'
\i.
Total :;
u.
(al
Vs &: Vp -= primary and secondary voltages.
!\p.\: :\5 = primary and secondary windinus.
Sketch:
Primary side (! )
Secondary side ( I )
Core (I)
How (If magnet iall ux (I)
The supply voltage will circulate On alternating magnetic nux in the core.
This flux wi 1.1 link with secondary winding !O induce emf.
The-induced emf will depend on the .iumber of turns in the secondary ~\,jllllillgS as well a" rare of
cLange of magnetic Ilux ,
Tilt: wmdi IIp turns (\1'1 ;tnd tcrmi nal voltage can he expressed a~
~1~
-r
(4 x I)
/\'r'
'\""
II.
li
l
I" '" ~(.l()VI('; :::'l'~,l~",l,
'!
12
1;1
1
\ ~" marks ,
l ! ooe
Let Ie'ol;l!')!'s he R and f<,
/,;~
1,
,\
-t-
"
rl
"
ti. .
N,
I
hen
number ('If
1)"1' ',,'('('Ild,
\1:11"11\'",1<: "Hll' p~;\k or ma ximum \:due measured,
[\'iilllilll,lIl1O: urne when tn ,-"Jinpkk" cyc!e .
fr('qut'llC\ till.'
t<
~ ,;
"
'J
!\
,I:~'
!
.\ , I
I
549
1,
___________________________________________________________________________________
_
(c)
(i) X
= 2~/l "" 2 x 3.14 .r 50 .r O.c)3 = 9.42fJ
(
I)
(I
i
Current
{ji)
tun /\
(.Ij
9.42 18R4 6'''(l4''
=XlR = -So
'-" ... == .0:.,'
v
0
(iii) Power factor
(I)
= Cosd: =: Cos 62.()4 == 0.4688
(I)
(iv) Apparent power = VI = 240 .r 22.5 = 5400W
(v) Active power
e
\If't~ds ~-) = 54(lO x 0.4688 "" 253L521,r
or alternativeiv
01'
(0)
(
I)
P
(I)
= I: R ~ 22.5:r 5: = 2531,25\\'
POLARITY TEST
Done 10 csrabl bb that
(i)
(it)
.;JIll
1\11 ruses and switches arc C,l!HlCCICd to live conductors only.
Socket outlets have the Ii ve conductor connected III the-terminals marked L
\cllIral (0 \ and earth 10 E.
The ccutre ('tmtad of bayonet and Edison screw lamp holder have their outer
contacts connected to earth conductors.
{j x I)
II KV generation
132KV transmission line
66KV secondary transmissron
.'13K V h.v. distribution
l1KV
415V 'lizati
240V
utt uauon
(, x I.
550
14.
Saft irOf\
nr...
'''''ot---ah,1!Id
--..,.,- Pe'r'rI.anen! magn.el
(6
x !.~)
T11<: mO\'lIl!! cuti .nstrurnent consist 01 a LOll made of copper wire wound in rectangular frame
and situated lB a magnetic field. l. 2 x I)
The pointer is mounted on bobbin
{Ii
The frame is attached to highly polished plV01 which resrs on jewels and rotates with minimum
friction
(I )
(I)
The controlling device has two hair springs wound in the opposite direction.
OPERr\TIO"
When the current riows in the end, it becomes a.11 clccrrornagneric producing its Own magnetic
held.
The coil field interacts With the permanent magnetic field to producing a turning force.
The magnitude of the turning force is determined by the current through tile coil.
Damping b achieved by eddy current and involve an aluminium device for damping.
(4
15.
(a)
P\,PTRA\SISTOR AVIPIJFJER
•
o
Correct itkn;ihulllOJI of P'\P
Common O[\!>{' configuration
Lab~I"llg input and output
(
1)
(l)
(ll
~,
,
~
:
I,
551
x J)
(b)
s
r-I
I
~
~
I
I
I
J
I
R
I
I
I
I
~
o~----------~-- '--'-----"'---~4
--~
Correct circuit connection:
Switch to transformer primary
-Tmnsformer secondary to bridge
-Bridgeto capacuor
-Capacitor to resistor
Resistor to 7.ener
(5
x )}
(l)
Correct polarity
Correct bl'iLige-
-(3)
Tota
l
552
9 marks