94
CHAPTER 17
(c)
The filament is tightly coiled
to fit the required length into a small space
(d) From
(
)
0
0
1
T
T
α
=
+
−
L
L
, where
(
)
1
6
4.5
10
C
α
−
−
=
×
°
, the length at
is
0
20 C
T
=
°
(
)
(
)
(
)
(
)
0
0
25 m
1
1
4.5
10
C
L
L
T
T
α
−
=
=
=
+
−
+
×
°
1
6
26 m
C
2 600 C
20
−
°
°
−
17.60
Each speaker has a resistance of
4.00
R
=
Ω
and can handle 60.0 W of power. From
, the maximum safe current is
2
I R
=
P
max
60.0 W
4.00
R
=
=
Ω
√
3.87 A
=
I
Thus, the system
is not adequately protected
by a 4.00 A fuse.
17.61
The crosssectional area of the conducting material is
(
)
2
2
outer
inner
A
r
r
π
=
−
Thus,
(
)(
)
(
)
(
)
5
2
2
2
2
2
3.5
10
m
4.0
10
m
1.2
10
m
0.50
10
m
L
R
A
ρ
π
−
−
−
×
Ω⋅
×
=
=
Ω
×
−
×
7
3.7
10
37 M
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 Spring '09
 Physics, Current, Resistance, Work, 2 m, 2 m, 25 m, 20°C, 2 600°C, 17.60 L

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