90
CHAPTER 17
(b)
The cost of operating the iron for 20 minutes is
(
)
(
)
5
6
1 kWh
8.6
10
J
$0.080
kWh
$0.019
1.9 cents
3.60
10
J
cost
E rate
=
⋅
=
×
=
=
×
17.51
Ohm’s law gives the resistance as
(
)
R
V
I
= ∆
. From
R
L A
ρ
=
, the resistivity is given by
(
)
R
A L
ρ
=
⋅
. The results of these calculations for each of the three wires are
summarized in the table below.
(
)
m
L
(
)
R
Ω
(
)
m
ρ
Ω⋅
0.540
10.4
6
1.41
10
−
×
1.028
21.1
6
1.50
10
−
×
1.543
31.8
6
1.50
10
−
×
The average value found for the resistivity is
6
av
1.47
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 Spring '09
 Physics, Current, Resistance, Work, Potential difference, ohm, Electrical resistance, Electrical impedance

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