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220
CHAPTER 21
(b) For an ideal transformer,
() ()
( )
av
av
2, rms
2, rms
input
ouput
VI
==
∆
PP
()
( )
Thus,
av
9.0
input
P
V
0.400 A
3.6 W
21.39
The power input to the transformer is
( )
5
1, rms
1, rms
3 600 V
50 A
1.8
10 W
input
=∆
=
=
×
P
For an ideal transformer,
( )
av
2, rms
2, rms
av
ouput
input
=
P
P
so the current in the long
distance power line is
5
av
2,rms
2, rms
1.8
1.8 A
100 000 V
input
I
V
×
=
∆
P
2
22
1.8 A
100
3.2
lost
line
IR
Ω
=
×
P
The power dissipated as heat in the line is then
The percentage of the power delivered by the generator that is lost in the line is
2
5
3.2
0%
100%
0.18%
1.8
×
=
×=
×
% Lost
10
lost
input
=×
P
P
21.40
(a) Since the transformer is to step the voltage
down
from 120 volts to 6.0 volts, the
secondary must have
fewer turns than the primary.
(b) For an ideal transformer,
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 Spring '09
 Physics, Current, Power, Work

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