81. Any thermodynamic cycle operating between two temperature limits is reversible if the product of the efficiency when operating as a heat engine and the COP when operating as a refrigerator is equal to l.

1. 1. True

   
   
   

   2. True/False

   
   
   

   3. False

   
   
   

   4. Both

   
   
   

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1. View Hint View Answer Discuss in Forum

   False
   η_HE × COP_HP = 1
   Where , HP = Heat pump
   

   Correct Option: C

   False
   η_HE × COP_HP = 1
   Where , HP = Heat pump
   

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82. When a system executes an irreversible cycle
    

1. 1. ∮	δQ	< 0
      	T

      
      

   
   
   

   2. ∮ dS > 0
      

   
   
   

   3. ∮	dQ	= 0
      	T

      
      

   
   
   

   4. ∮	δQ	> 0
      	T

   
   
   

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1. View Hint View Answer Discuss in Forum

   ∮	δQ	< 0 clausius inequality
   	T

   
   

   Correct Option: A

   ∮	δQ	< 0 clausius inequality
   	T

   
   

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83. Figure below shows a reversible heat engine ER having heat interactions with three constant temperature systems. Calculate the thermal efficiency of the heat engine
    
    

1. 1. 60%

   
   
   

   2. 30%

   
   
   

   3. 20%

   
   
   

   4. 5%

   
   
   

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1. View Hint View Answer Discuss in Forum

   Q₁ + Q₂ - Q₃ = W .... (i)
   

   	Q1	+	Q2	-	Q3	= 0 ...... (ii)
   	1000		500		300

   
   From equation (ii) , we have
   

   	Q1	+	Q2	-	Q3	= 0
   	1000		500		300

   
   ⇒ Q₃ = 60 kJ
   W ⇒ 100 + 50 - 60 = 90 kJ
   

   η =	W	=	90	= 60%
   	Q1 + Q2		150

   
   

   Correct Option: A

   Q₁ + Q₂ - Q₃ = W .... (i)
   

   	Q1	+	Q2	-	Q3	= 0 ...... (ii)
   	1000		500		300

   
   From equation (ii) , we have
   

   	Q1	+	Q2	-	Q3	= 0
   	1000		500		300

   
   ⇒ Q₃ = 60 kJ
   W ⇒ 100 + 50 - 60 = 90 kJ
   

   η =	W	=	90	= 60%
   	Q1 + Q2		150

   
   

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84. A reversible heat transfer demands :
    

1. 1. The temperature difference causing heat transfer tends to zero
      

   
   
   

   2. The system receiving heat must be at a constant temperature
      

   
   
   

   3. The system transferring out heat must be at a constant temperature
      

   
   
   

   4. Both interacting systems must be at constant temperatures

   
   
   

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1. View Hint View Answer Discuss in Forum

   ∆S = 0
   

   ⇒	δQ	-	δQ	= 0
   	T1		T2

   
   ⇒ T₁ = T₂

   Correct Option: A

   ∆S = 0
   

   ⇒	δQ	-	δQ	= 0
   	T1		T2

   
   ⇒ T₁ = T₂

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85. A condenser of a refrigeration system rejects heat at a rate of 120 kW, while is compressor consumes a power of 30 kW. The coefficient of performance of the system would be
    

1. 1. 1

      4

      
      

   
   
   

   2. 4
      

   
   
   

   3. 1

      3

      
      

   
   
   

   4. 3

   
   
   

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1. View Hint View Answer Discuss in Forum

   Q₁ = 120 kW , W = 30 × kW , Q₂ = 120 – 30 = 90kW
   
   

   (COP)ref =	Q2	=	90	= 3
   	W		30

   
   

   Correct Option: D

   Q₁ = 120 kW , W = 30 × kW , Q₂ = 120 – 30 = 90kW
   
   

   (COP)ref =	Q2	=	90	= 3
   	W		30

   
   

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