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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
cost
E rate
=⋅
=×
=
=
×
17.51
Ohm’s law gives the resistance as
( )
RV
I
= ∆
. From
RL
A
ρ
=
, the resistivity is given by
( )
RA
L
. The results of these calculations for each of the three wires are
summarized in the table below.
( )
m
L
( )
R
Ω
( )
m
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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