dc principles

7/26/2019 DC Principles

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Electric Current Flow

EMF

Positive

Terminal

NegativeTerminal


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15. $+#3-"4.6 ,"$*# 0/ 9$*.# "*. 8$:.+ " /3*45.* ,*04.%4$:. %0"4$+8 ;7 .+%-0#$+845.2 $+ " )h( 0* ,0-7.457-.+. S"% \. %"-- 45$# S"%

M)G'$2 D9+0 9"-B)21&2& +K)-#2& 07)$

O> 07)$


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>/> Q2-)-#%$-

>/>/.

@ *.#$#40* $# " %02,0+.+4 45*0385 95$%5 %3**.+4 /-09# ;34 95$%5 .?5$;$4#%0+%.+4*"4.6 *.#$#4"+%. 40 45. %3**.+4 /-09> Q+ #02. 4.-.%0223+$%"4$0+#

#7#4.2#R 45.*. $# " +..6 40 *.#4*$%4 %3**.+4 /-09 0* %0+4*0- %3**.+4 /-09 ;7 "66$+8 resistance at a particular point in the #7#4.2>

The unit of resistance is the ohm with the symbol . =.#$#40*# %02. $+ " 9$6. *"+8. 0/ ,57#$%"- #$g.# "+6 ,"% O$83*. A #509# .?"2,-.# 0/ *.#$#40*#>

M)G'$2 E+B$22 +5,2- %3 Q2-)-#%$

a) Wire Wound Resistor

b) Carbon Resistor

(P F2#71 M)18 Q2-)-#%$


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>/>/6

=.#$#40*# "*. 2"6. "# -09 "# I 052 "+6 "# 5$85 " IB 2.8052# 0* IB T >

Meg or M for short, stands for one million. P0 IB T b IB 2$--$0+ 052#>

Kilo or k for short, stands for one thousand. P0 " [ < *.#$#40* b[RBBB 052#>

>/>/:

@# " 8.+.*"- *3-. 95.+ %3**.+4 /-09# 45*0385 " *.#$#40*R $4 5."4# 3, 45. *.#$#40*>15. *.#$#40* #3*/"%. 23#4 45.+ *"6$"4. 5."4> Q/ 45. *.#$#40* $# +04 -"*8. .+0385 40*"6$"4. 45. 5."4 ,*063%.6 ;7 45. %3**.+4 /-09 45*0385 $4R $4 9$-- ;.%02. :.*7 504R$4 2"7 8-09 "+6E0* 2"7 2.-4E;3*+ 034>

M)G'$2 H0%K2$ ;)--),7#2& 7- T27#

=.#$#40*# 45.*./0*. 5":. " *"4$+8 40 $+6$%"4. 509 23%5 %3**.+4 %"+ /-09 45*038545.2 %0+4$+303#-7 9$45034 5."4 6"2"8.>

This rating is called their power rating and the unit for electrical pow .* *"4$+8 $#the watt with the symbol w.

=.#$#40*# 95$%5 "*. ,57#$%"--7 #2"-- $+ #$g. 2"7 ;. *"4.6 "# IEZ 9"44 0* IEX 9"44>

a"*8.* *.#$#40*# 2"7 5":. " [ 0* IB 9"44 *"4$+8>

15. ;"#$% *.#$#40* %0-03* %06. $# 6.4"$-.6 $+ @,,.+6$? @

Current Flow


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M)G'$2 .J4V78,12- 7"& Q217#)N2 @)W2- %3 0%K2$ Q2-)-#%$-

15$# ,09.* 6$##$,"4.6 $# 0;4"$+.6 ;7 23-4$,-7$+8 45. :0-4"8. ",,-$.6 40 45.

*.#$#40* ;7 45. %3**.+4 /-09 45*0385 $4R 8$:$+8 45. ,09.* 6$##$,"4.6 $+ 9"44#Nh ? Q b \

\5.*. h b :0-4"8. ",,-$.6 40 45. *.#$#40* $+ :0-4#Q b %3**.+4 /-09 45*0385 $4 $+ "2,#\ b ,09.* 6$##$,"4.6 $+ 45. *.#$#40* $+ 9"44#


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>/>/> X7$)7S12 Q2-)-#%$-

O$83*. II #509# #02. :"*$";-. *.#$#40*#>

Q+ ."%5 %"#. 45.*. $# " %0+4*0- 95$%5 "--09# 45. "203+4 0/ *.#$#4"+%. ;.49..+ $4#.+6 %0++.%4$0+# 40 ;. :"*$.6>

M)G'$2 ..4V78,12- %3 X7$)7S12 Q2-)-#%$-


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>/>/? ;$7K)"G -58S%1 3%$ $2-)-#%$

Q+ .-.%4*$%"-E4.-.%0223+$%"4$0+# 6*"9$+8# " ,57#$%"- #72;0- $# 3#.6 40 *.,*.#.+4" *.#$#40*> O$83*. IX> P509# 45. 6*"9$+8 #72;0-# 3#.6 40 *.,*.#.+4 ;045 /$?.6"+6 :"*$";-. *.#$#40* .-.2.+4#>

M)G'$2 .6


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F?"2,-.# 0/ %","%$40* #5",.# "*. #509+ $+ O$83*. IV K"M>

15. #72;0- /0* " /$?.6 %","%$40* $# #509+ $+ O$83*. IV K;M>

15. %$*%3$4 #72;0- /0* " %","%$40* $# #509+ $+ O$83*. IV K%M>

M)G'$2 .: O7P


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>/A @K)#(B2-

@ #9$4%5 $# " ,57#$%"- %$*%3$4 %02,0+.+4 95$%5 %"+ .$45.* %02,-.4.-7 #40, 45./-09 0/ .-.%4*$%"- %3**.+4R 0* $/ 0,.*"4.6R %"+ "--09 45*0385 45. /-09 0/ .-.%4*$%"-%3**.+4 9$45034 "+7 $2,.6$2.+4>

M)G'$2 .>

K"M #9$4%5 %-0#.6 K;M #9$4%5 0,.+K2"


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>/D =--2--82"# L'2-#)%"-

I> G"2. 45*.. #03*%.# 0/ FTO]

"M YYYYYYYYYYYYYYYYYYYYYYYYYYYY

;M YYYYYYYYYYYYYYYYYYYYYYYYYYYY

%M YYYYYYYYYYYYYYYYYYYYYYYYYYYY

X> '*"9 45. %$*%3$4 #72;0- /0* " ;"44.*7 cell

V> '*"9 45. ;"44.*7 #72;0- /0* 23-4$,-. %.--# #3%5 "# 45. 4.-.,50+..?%5"+8. ;"44.*7 "+6 $+6$%"4. $4# 4.*2$+"- :0-4"8.>

Z> @ 9$*. 3#.6 /0* %0+63%4$0+ 0/ .-.%4*$%$47 $# " %0+63%40* %0:.*.6 $+$+#3-"4$0+ 2"4.*$"-> '$//.*.+4 $+#3-"4$0+ 2"4.*$"-# "*. 3#.6 /0* $+600* "+6

034600* 9$*.#E%";-.#> P4"4. 45. $+#3-"4$0+ 2"4.*$"- 3#.6 "+6 95.45.* 3#.6$+600* 0* 034600*>

"M O0* $+600*R 45. $+#3-"4$0+ 2"4.*$"- $#

YYYYYYYYYYYYYYYYYYYYYY

;M O0* 034600*R 45. $+#3-"4$0+ 2"4.*$"- $#



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[> '*"9 " 6$"8*"2 #509$+8 45. ,"*4# 0/ " %";-. 3#.6 /0* 4.-.,50+.E6"4"%0++.%4$0+# "+6 -";.- 450#. ,"*4#>

J> P4"4. 45. 3+$4 0/ *.#$#4"+%. "+6 $4# #72;0->

"M 15. 3+$4 0/ *.#$#4"+%. $# 45. YYYYYYYYYYY

;M 15. #72;0- /0* 45. 3+$4 0/ *.#$#4"+%. $# YYYYYYYYYY

^> State the meaning of kilo when used in describing the magnitude 0/*.#$#4"+%.N

kilo means _________ YYYYYYYYY

A> \5"4 60.# IB T 2."+ ]

YYYYYYYYYYYYYYYYYYYYYYYYYYYYY

H> '*"9 45. #72;0- /0* " /$?.6 *.#$#40*>

IB> '*"9 45. #72;0- /0* " :"*$";-. *.#$#40*


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II> '*"9 45. #72;0- /0* " %","%$40*

IX> P4"4. 490 /3+%4$0+# 0/ " %","%$40* $+ 4.-.,50+. #7#4.2#>

"M YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

;M YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

IV> '*"9 45. #72;0- /0* " #9$4%5 $+ 45. %-0#.6 K2"

IZ> '*"9 45. #72;0- /0* " #9$4%5 $+ 45. 0,.+ K;*."


30/67

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15. .-.%4*$%"- ,*.##3*. 45.+ /0*%.# %3**.+4 /-09 "*03+6 45. %$*%3$4 45*0385 45..-.%4*$%"- %02,0+.+4#>

@ 47,$%"- .-.%4*$% %$*%3$4 2$854 %0+#$#4 0/ " ;"44.*7R " #9$4%5R %0++.%4$+8 9$*.# "+6" -"2,>

15$# $# #509+ $+ O$83*. IJ>

M)G'$2 .A+5,)(71 412(#$)(


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!"#$% '( )*$+%$,-.# /0* 1.-.%0223+$%"4$0+# 1340*$"-


?/:

Q+ O$83*. I^R 45. :0-4"8. ",,-$.6 40 45. %$*%3$4 $# IX :0-4#R "+6 45. 404"-*.#$#4"+%. $# J 052#>

Q b h k =Q bIX k JQ b 6 78,-/ @ %3**.+4 0/ X "2,# 9$-- /-09 45*0385 45. %$*%3$4>

Lets make the EMF source a 24v battery. What be the current flow now around45. %$*%3$4]

Q b h k =Q b XZ k JQ b > 78,- >

_03 9$-- +04$%. 45"4 "# 45. FTO $# $+%*."#.6R #0 45. %3**.+4 $# $+%*."#.6>

G09 9. 9$-- $+%*."#. 45. *.#$#4"+%. /*02 J 052# 40 IX 052# "+6 -.":. 45. FTO"4 IX:>

Q b h k =Q b IX k IXQ b . 78,/

G04. 45"4 "+ )"($27-2 )" $2-)-#7"(2 *.#3-4# $+ " &2($27-2 )" ('$$2"#/

This formula is called :47' ;"3 and it is a very fundamental formula in.-.%4*$%"- 90* Q+ 40,$% J 703 9$-- 60 ;"#$% 4.-.,50+. +.490*< %"-%3-"4$0+#3#$+8 052# -"9>

12 v 6

Q in am s


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!"#$% '( )*$+%$,-.# /0* 1.-.%0223+$%"4$0+# 1340*$"-


?/> Ohms Law

Ohms Law is probably t 5. 20#4 $2,0*4"+4 .-.%4*$%"- *.-"4$0+#5$, 703 9$--.+%03+4.*> Q4 $# 45. ;"#$% -"9 0/ %3**.+4 /-09>

@ `.*2"+ ,57#$%$#4R `.0*8 P$20+ DWT KI^A^ IA[ZM 6$#%0:.*.6 45$#

*.-"4$0+#5$, $+ IAX^>

\5.+ "+ .2/ $# ",,-$.6 40 " *.#$#40* " 20:.2.+4 0/ %5"*8.# $# ,*063%.6> 15.*"4. 0/ 20:.2.+4 0/ 450#. %5"*8.# K%3**.+4M $# 6$*.%4-7 *.-"4.6 40 45. ",,-$.6:0-4"8.> Q/ 45. ",,-$.6 :0-4"8. $# 603;-.R 45.+ 45. %3**.+4 $# "-#0 603;-.6,*0:$6.6 45. *.#$#4"+%. *.2"$+# %0+#4"+4>

Ohms Law is expressed by:


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!"#$% '( )*$+%$,-.# /0* 1.-.%0223+$%"4$0+# 1340*$"-


X

!

Q

12 v 10

I>X am s

With this limitation in mind, Ohms Law can be written in three ways:

h b Q ? =

= b h k Q

Q b h k =

Q/ "+7 490 L3"+4$4$.# "*. X "2,#R 9. 903-6 /$+6 45. :0-4"8. ;7N

h b Q ? =h b I>X ? IBh b .6 N%1#-


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?/? @2$)2- 15. *.#$#40*# "*. *.8"*6.6 "# ;.$+8 $+ ,"*"--.->@ ,"*"--.- %0++.%4$0+ $# ,*.#.+4 95.+ 45. %02,0+.+4# 6$:$6. 45. %3**.+4>

12 v

Q in amps 100

100

600


35/67

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15. ,"*"--.- %$*%3$4# 9$-- ,*0:$6. .?4*" %3**.+4 ,"45# "+6 5.+%. " -"*8.* 0:.*"--%3**.+4> Q4 $# 45.*./0*. *."#0+";-. 40 .?,.%4 -.## 404"- *.#$#4"+%. /0* "+ $+%*."#.$+ 404"- %3**.+4> 15$# %"+ ;. ,*0:.6 "# /0--09#>

9-)"G ZB ms Law:

QI b h I k = I

QX b h X k = X

Q1 b h P k = 1

\5.*. = 1 $# 3#.6 40 *.,*.#.+4 45. 404"- *.#$#4"+%.>


36/67

!"#$% '( )*$+%$,-.# /0* 1.-.%0223+$%"4$0+# 1340*$"-


200 200

?/D =--2--82"# L'2-#)%"-

I> j#$+8 45. %0**.%4 #72;0-#R 6*"9 "+ .-.%4*$% %$*%3$4 %0+#$#4$+8 0/ " H:;"44.*7R " #9$4%5R "+6 "+ IA 052 *.#$#40*>

X> \$45 45. #9$4%5 $+ 45. %-0#.6 ,0#$4$0+R %"-%3-"4. 45. %3**.+4 95$%5903-6 /-09 "*03+6 45. %$*%3$4 0/ [>I>

15. %3**.+4 903-6 ;. YYYYYYYYYYYYY

V> Q/ 45. ;"44.*7 :0-4"8. $+ 703* %$*%3$4 0/ [>I 9"# $+%*."#.6 40 IX :0-4#R903-6 45. %3**.+4 /-09$+8 $+ 45. %$*%3$4 $+%*."#. 0* 6.%*."#.]

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Z> Q/ 703 $+%*."#. 45. *.#$#4"+%. 0/ " %$*%3$4 903-6 45. %3**.+4 /-09$+%*."#. 0* 6.%*."#.]


[> Q/ 703 Q+ " ,"*"--.- %$*%3$4 9$45 6$//.*.+4 *.#$#40* :"-3.#R $# 45. 404"- *.#$#4"+%.5$85.* 45"+ 45. -"*8.#4 *.#$#40* :"-3.R -09.* 45"+ 45. -09.#4 *.#$#40* :"-3.R0* #02.95.*. $+ ;.49..+]


^> '.4.*2$+. 45. 404"- *.#$#4"+%. 0/ 45. %$*%3$4 ;.-09>



37/67

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15. "88*.8"4. 0/ "-- 45. 4.-.,50+. %0++.%4$0+# /*02 502. 40 4.-.,50+.exchange is called, collectively, the Customers Access Network or CAN forshort. Electrically, this local loop looks like the circuit in Figure 19.

M)G'$2 .HC%(71 C%%, +212,B%"2


38/67

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M)G'$2 6JC%(71 1%%, +212,B%"2 BB[ "2,# 40 2$--$"2,#>B>BB[ ? IBBB b ? 8=


39/67

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A/: ="%#B2$ C%(71 C%%, BZ "2,>(0+:.*4$+8 40 2$--$"2,#NB>BZ ? IBBBb >J 8=


40/67

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A/> =--2--82"# L'2-#)%"-

I> State the meaning of the abbreviation mA?

mA means ___________________

X> (0+:.*4 B>BV @2,# 40 2$--$"2,#

B>BV @2,# b YYYYYYYYY 2$--$"2,#

V> (0+:.*4 B>BB[ @ 40 2@>

B>BB[ @ b YYYYYYY 2@

Z> F?"2$+. 45. O$83*. ;.-09> \5"4 $# 45. 404"- *.#$#4"+%. ;.49..+ 45. 490;"44.*7 4.*2$+"-# 80$+8 "*03+6 45. %$*%3$4 %-0% ("-%3-"4. 45. %3**.+4 /-09 "*03+6 45. %$*%3$4 0/ 45. /$83*. #509+ $+L3.#4$0+ Z>

Q b YYYYYYY 2@

200!" $ %&


41/67

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Voltages as low as 24 v may cause the tingling sensation but this level of:0-4"8. $# +0*2"--7 %0+#$6.* +0+U-.45"- "+6 $+ /"%4 :0-4"8.# 3, 40 JB : 6% "+6ZX>Z : "% K,."


42/67

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D+%. 45. # (3**.+4/-09$+8 ;.49..+ 45.#. 490 ,0$+4# K0+. /$+8.* 40 45. 045.* 0+ 45. #"2. 5"+6M $#+04 #0 #.*$03# "# O$83*. K;M> O$83*. K;M #509# 45. ,0$+4# 0/ %0+4"%4 ;.$+8 45. 4905"+6# 9$45 %3**.+4 /-09$+8 45*0385 ;067 "+6 ,0##$;-. :$" 45. 5."*4> 15$# $# "serious situation as the hearts nervous system may therefore be directly"//.%4.6>

e3$4. #2"-- "203+4 0/ %3**.+4 2"7 5":. " 2"S0* .//.%4 0+ 45. 532"+ ;067>


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1";-. X #509# 47,$%"- -.:.-# 0/ %3**.+4 "+6 45.$* -$412(#$)( M2"(2

D45.* 6"+8.*03# .//.%4# 0/ .-.%4*$% #50%< %"+ ;. $+6$*.%4>

O0* .?"2,-.R " ,.*#0+ 0+ " -"66.* 2"7 8.4 " -09 -.:.- .-.%4*$% #50%< 95$%5%"3#.# 45.2 40 40,,-. 0// 45. -"66.* "+6 #3#4"$+ $+S3*7 45*0385 45. /"-->


44/67

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D/: U7-)( Q'12- %$ 0$2(7'#)%"- =G7)"-# 412(#$)( @B%(Y

Q4 $# +04 ,0##$;-. 40 #4"4. 9$45 %.*4"$+47 " #"/. :0-4"8. -.:.->

Q4 :"*$.# 9$45 45. ,.*#0+ "+6 45. .+:$*0+2.+4>

@ #"/. :0-4"8. %0+4"%4.6 3+6.* 6*7 %0+6$4$0+# 9$45 6*7 5"+6# 2"7 ;. 6"+8.*03#3+6.* 532$6 %0+6$4$0+# 9$45 9.4 5"+6#>

=.2.2;.* 45"4 45. %3**.+4 ,"45 $# 0/4.+ ;.49..+ 0+. ,0$+4 0+ 45. .-.%4*$%.L3$,2.+4E",,-$"+%.E%$*%3$4E%";-.E4.*2$+"- "+6 F@=1W>

Earth may be the metal part of a refrigerator (which ought to be earthed) or45. 2.4"- ,"*4 0/ "+ .-.%4*$% 40"#4.* K95$%5 03854 40 ;. ."*45.6 0* $+6..6 45.2.4"- 90*< "##0%$"4.6 9$45 " ;3$-6$+8 0* "+ .+%-0#3*. 0/ .-.%4*$%"- .L3$,2.+4R"8"$+ 95$%5 03854 40 ;. ."*45.6>

(0+#$6.* 45. /0--09$+8 ;"#$% 90*;M Dont rely on other persons checks; check yourself. %M @ :0-4 2.4.* K23-4$U2.4.*M 0* .L3$:"-.+4 6.:$%. $# 6.#$8+.6 40 6.4.*2$+.

45. :0-4"8. ;.49..+ 490 ,0$+4#> j#. 45$# 6.:$%. 40 %5.%< /0* 5"g"*603#:0-4"8.# ;.$+8 ,*.#.+4> @ :0-4 2.4.* %5.%< ;.49..+ 45. .?,0#.6metallic/terminals/frame/conductors and earth will help determine if a5"g"*603# #$43"4$0+ $# ,*.#.+4>

6M Dont work in "+ .-.%4*$%"- .+:$*0+2.+4 9$45 9.4 5"+6# 0* 0+ 9.4/-00*# 0* 3#. 9.4 400-#>

.M j#. ",,*0,*$"4. ,*04.%4$:. %-045$+8 -$

/M When working near or live electrical apparatus wear tight U/$44$+8 %-045#9$45034 2.4"- 45*."6# "+6 ,0##$;-. 9$45034 2.4"- /$44$+8# "+6 ;. "-.*4 "4"-- 4$2.#>

8M G.:.* 90*< 0+ .-.%4*$%"- ",,"*"43# 95.+ 3+6.* 45. $+/-3.+%. 0/ 6*38# 0*"-%050- 0* 95.+ 703 "*. 4$*.6>

5M Dont wear conductive jewellery which might contact live termi +"-#l.:.+ 2.4"--$% *$+8# "+6 9"4%5.# %"+ ,*.#.+4 " 5"g"*6 $+ .-.%4*$%"-.+:$*0+2.+4#>

$M \5.*.:.* ,0##$;-. #9$4%5 45. ,09.* 0// "+6 3+,-38 "+6 95.*.",,*0,*$"4.R 6$#%5"*8.R .-.%4*$%"- ",,"*"43# ;./0*. 90*


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D/> Q2"&2$)"G =--)-#7"(2 #% 7 02$-%" @'332$)"G 3$%8 412(#$)(@B%(Y

"M Q4 $# .##.+4$"- 40 "%4 ,*02,4-7 $/ 703 #3#,.%4 " ,.*#0+ $# $+ 6$//$%3-4$.#"+6 $# ;.$+8 #3;S.%4.6 40 .-.%4*$% #50%

;M Q4 $# .##.+4$"- "%# #% ,'# 5%'$-213 7# $)-Y "-#0 "# 703 9$-- +04 ;. 0/ "+7

"##$#4"+%. $/ 703 "-#0 ;.%02. #3;S.%4 40 .-.%4*$% #50%%M P..< 40 L3$% j#. "+ $+#3-"40* 40 6*"8 " ,.*#0+ 0// 45.$* ,0$+4 0/%0+4"%4 9$45 45. 5"g"*6 2"/M ("-- /0* "##$#4"+%. if possible phone emergency on 000

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