This preview shows page 1. Sign up to view the full content.
Current and Resistance
87
17.44
The energy used was
3
$200
2.50
10 kWh
$0.080 kWh
cost
E
rate
==
=×
The total time the furnace operated was
3
2.50
104 h
24.0 kW
E
×
=
P
t
, and since
January has 31 days, the average time per day was
104 h
3.36 h d
31.0 d
average daily operation
17.45
The energy saved is
and the monetary savings is
()
(
)
3
40 W
11 W
100 h
2.9
10 Wh
2.9 kWh
high
low
Et
∆=
−
⋅=
−
=
×
=
PP
( )
( )
2.9 kWh
$0.080 kWh
$0.23
23 cents
savings
E rate
=∆ ⋅
=
=
=
17.46
The power required to warm the water to 100°C in 4.00 min is
( )
( )
( )( )
2
0.250 kg
4 186 J kg °C
100 C
20°C
3.5
10 W
4.00 min
60 s 1 min
mc
T
Q
tt
⋅°
−
∆
∆
=
∆∆
P
The required resistance (at 100°C) of the heating element is then
This is the end of the preview. Sign up
to
access the rest of the document.
 Fall '10
 STAFF
 Physics, Current, Resistance, Energy

Click to edit the document details