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Current and Resistance
83
(b) The energy used by the oven in 5.0 h is
()
3
1 kW
20.0 C s
220 J C
5.0 h
22 kWh
10 J s
Et
I
Vt
=⋅∆=
∆
⋅∆=
=
P
and the cost of this energy, at a rate of $0.12 per kilowatt-hour is
( )
22 kWh
$0.12 kWh
$2.6
cost
E rate
=⋅
=
=
17.33
The maximum power that can be dissipated in the circuit is
( ) ( )( )
3
max
max
120 V
15 A
1.8
10 W
VI
=∆
=
=
×
P
Thus, one can operate at most
18 bulbs rated at 100 W per bulb.
17.34
(a) The power loss in the line is
( )
( )
2
2
7
1000 A
0.31
km
160 km
5.0
50 MW
loss
IR
==
Ω
=×
=
P
(b) The total power transmitted is
( )( )
38
700
10 V
7.0
700 MW
input
=
×
=
×
=
P
Thus, the fraction of the total transmitted power represented by the line losses is

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