- #1
duran9987
- 12
- 2
Homework Statement
The temperature inside the room ##T_I= 25 C ## and the temperature outside the house is ##T_O = 32C##. The temperature difference causes energy to flow into the room (by conduction through the walls and window glass) at the rate 3,000 J/s. To return this energy to the outside by running an ideal refrigerator, how much electrical energy must be supplied to the refrigerator (to perform the external work)?
Homework Equations
##Q_h=W_{in}+Q_c##, Energy Conservation
##Efficiency = 1 - T_c/T_h=(Q_h-Q_c)/Q_h##
The Attempt at a Solution
My thinking is that we have to put in work so that the refrigerator takes energy from the cold reservoir and dumps 3000 Joules onto the hot reservoir. This leads me to set ##Q_h=3000## and use the efficiency to find ##Q_C## and eventually solve for ##W_{in}##.
##Efficiency = 1 - (298.15K/305.15K) = 0.02264##
##0.02264 = (3000-Q_c)/3000 ⇒ Q_c = 2931.19J##
##W_{in} = 3000J-2931.19J = 68.82J##
Is my approach correct? seems like a small amount of energy needed to dump 3000J back to the outside. Any feedback (or more efficient methods) would be greatly appreciated.