78
CHAPTER 17
17.16
We assume that your hair dryer will use about 400 W of power for 10 minutes each day
of the year. The estimate of the total energy used each year is
(
)
(
)
(
)
min
1 hr
0.400 kW
10
365 d
24 kWh
d
60 min
E
t
=
∆
=
=
P
(
)
If your cost for electrical energy is approximately ten cents per kilowatthour, the cost of
using the hair dryer for a year is on the order of
$
24 kWh
0.10
$2.4
or
~$1
kWh
cost
E
rate
=
×
=
=
17.17
The resistance is
9.11 V
0.253
36.0 A
V
R
I
∆
=
=
=
Ω
, so the resistivity of the metal is
(
)
(
)
(
)
(
)
2
2
3
8
4
0.253
2.00
10
m
1.59
10
m
4
50.0 m
R
d
R A
L
L
π
π
ρ
−
−
⋅
Ω
×
⋅
=
=
=
=
×
Ω⋅
Thus, the metal is seen to be
silver .
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 Spring '09
 Physics, Current, Resistance, Energy, Power, Work, electrical energy

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