11. Thermal conductivity is lower for
    

1. 1. wood
      

   
   
   

   2. air
      

   
   
   

   3. water at 100°C
      

   
   
   

   4. steam at 1 bar

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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12. Match the property with their units
    

    Property	Units
    A. Bulk modulus	1. W/s
    B. Thermal conductivity	2. N/m2
    C. Heat transfer coefficient	3. N/m3
    D. Heat flow rate	4. W
    	5. W/mK
    	6. W/m2K

    
    

1. 1. A - 1 , B - 2 , C - 6 , D - 5
      

   
   
   

   2. A - 2 , B - 5 , C - 6 , D - 1
      

   
   
   

   3. A - 2 , B - 6 , C - 4 , D - 1
      

   
   
   

   4. A - 1 , B - 5 , C - 3 , D - 2

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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13. For a given heat flow and for the same thickness, the temperature drop across the material will be maximum for
    

1. 1. Copper
      

   
   
   

   2. Steel
      

   
   
   

   3. Glass wool
      

   
   
   

   4. Refractory brick

   
   
   

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1. View Hint View Answer Discuss in Forum

   dT ∝	1
   	K

   
   So, glass wool has minimum thermal conductivity and therefore maximum temperature difference.

   Correct Option: C

   dT ∝	1
   	K

   
   So, glass wool has minimum thermal conductivity and therefore maximum temperature difference.

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14. Match Group with Group B:
    

    Group A	Group B
    A: Biot number	1: Ratio of buoyancy to viscous force
    B: Grashoff number	2: Ratio of inertia force to viscous force
    C: Prandtl number	3: Ratio of momentum to thermal diffusivities
    D: Reynolds number	4: Ratio of internal thermal resistance to boundary layer thermal resistance

    
    

1. 1. A - 4 , B - 1 , C - 3 , D - 2
      

   
   
   

   2. A - 4 , B - 3 , C - 1 , D - 2
      

   
   
   

   3. A - 3 , B - 2 , C - 1 , D - 4
      

   
   
   

   4. A - 2 , B - 1 , C - 3 , D - 4
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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15. The temperature variation under steady heat conduction across a composite slab of two materials with thermal conductivities k₁ and k₂ is shown in figure then, which one of the following statements holds?
    
    

1. 1. k₁ > k₂
      

   
   
   

   2. k₁ = k₂
      

   
   
   

   3. k₁ = 0
      

   
   
   

   4. k₁ < k₂

   
   
   

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1. View Hint View Answer Discuss in Forum

   Q = KA	dt
   	dx

   
   

   where Slope =	dt	=	Q
   	dx		KA

   
   i.e., slope is more for less value of K, therefore
   

   	dt			>		dt
   	dx		Ⅰ material			dx		Ⅱ material

   
   ∴ K₁ < K₂

   Correct Option: A

   Q = KA	dt
   	dx

   
   

   where Slope =	dt	=	Q
   	dx		KA

   
   i.e., slope is more for less value of K, therefore
   

   	dt			>		dt
   	dx		Ⅰ material			dx		Ⅱ material

   
   ∴ K₁ < K₂

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