1 L of 20 degree C water is placed in a refrigerator. The refrigerator's motor must supply an extra 8 W to chill the water to 5 degrees C in 1 hr. What is the refrigerator's coefficient of performance?
The Attempt at a Solution
8W = 8 J/s * 3600 s = 28,800 J -- this is the work in - Win
1L of H20 has mass 1kg and c=4190 J/kgK
so Q=(1Kg)(4190)(-15) = -62850 J --- this is the heat extracted from cold reservoir - Qc
K= Qc/Win so K = 62850J/28800J K= 2.18