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84
CHAPTER 17
17.36
(a)
()
(
)
( )( )
5
90 W
1 h
90 J s
3 600 s
3.2
10 J
=⋅=
=
=
×
P
Et
(b) The power consumption of the color set is
()( )
( )
120 V
2.50 A
300 W
VI
=∆
=
=
P
Therefore, the time required to consume the energy found in (a) is
5
3
3.2
1 min
1.1
10 s
18 min
300 J s
60 s
E
t
×
==
= ×
=
P
17.37
The energy input required is
( )
( )( )
5
1.50 kg
4 186 J kg
C
50.0 C
10.0 C
2.51
Em
cT
=
⋅
°
°
−°
=×
10.0 min
600 s
t
and, if this is to be added in
∆
, the power input needed is
5
2.51
419 W
600 s
E
t
×
=
∆
P
The power input to the heater may be expressed as
2
VR
P
, so the needed
resistance is
22
120 V
34.4
419 W
V
R
∆
=Ω

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