Question

Imagine an ideal (Carnot) refrigerator that keeps helium in its liquid state, at a temperature of about 4.00 KK . The refrigerator, with the helium container inside, is in a laboratory where the temperature is about 294 KK . Because of the imperfection of the insulation, 2.00 JJ of heat is absorbed by the refrigerator each hour. How much electrical energy EEE must be used by the refrigerator to maintain a temperature of 4.00 KK inside for one hour

Answer 1

Known :

Tc = 4 K

Th = 294 K

Qc = 2 J

Solution :

Using COP definition

COP = Tc / (Th - Tc)

COP = 4 / (294 - 4)

COP = 2 / 145

COP = Qc / W

2 / 145 = 2 / W

W = 145 J

Electrical energy used

E = W / t

E = 145 / 1

E = 145 J/h