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Question:

The temperature inside a refrigerator is t2°C and the room temperature is t1°C. The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be?

t2+273/t1−t2

t1/t1−t2

(t1+t2)/(t1+273)

(t1+273)/(t1−t2)

Solution:

The correct option is (t1+273)/(t1−t2)
Heat delivered = Q1
Coefficient of performance = β = Q2/W = Q1−W/W = Q1/W − 1 = T2/(T1−T2) ⇒ Q1/W = 1 + (t2+273)/(t1−t2) = (t1+273)/(t1−t2)