Thermal conductivity of a conducting solid material depends upon its_______________?

Related Mcqs:

1. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of ‘a’ in SI system will be________________?

   A. W/m.k
   B. W/m
   C. W/m.k2
   D. None, ‘a’ is just a number

2. For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally ?

   A. Decreases
   B. Increases
   C. Remains unchanged
   D. Increases exponentially

3. Low thermal conductivity of heat insulating materials is due to its_______________?

   A. Dense structure
   B. High proportion of air space
   C. High specific heat
   D. None of these

4. 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?

   A. 0.5
   B. 0.05
   C. 0.1
   D. 0.15

5. A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is ______________ °C?

   A. 6
   B. 12
   C. 18
   D. 24

6. A composite flat wall of a furnace is made of two materials ‘A’ and ‘B’. The thermal conductivity of ‘A’ is twice of that of material ‘B’, while the thickness of layer of ‘A’ is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material ‘A’ is________________?

   A. 125
   B. 133
   C. 150
   D. 160

7. With increase in porosity, the thermal conductivity of a solid substance__________________?

   A. Increases
   B. Decreases
   C. Remains unchanged
   D. May increase or decrease; depends on the solid

8. _____________ equation relates the thermal conductivity of a solid to its temperature ?

   A. Antoine
   B. Kopp’s
   C. Lee’s
   D. Kistyakowsky

9. In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is______________________?

   A. 2000
   B. 4000
   C. 5000
   D. 6000

10. The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface) ?

    A. K/h0
    B. 2K/h0
    C. h0/K
    D. h0/2K