Thermal diffusivity of a substance is proportional to (where, k = Thermal conductivity) ____________________?

Related Mcqs:

1. A furnace is made of a refractory brick wall of thickness 0.5 metre and thermal conductivity 0.7 W/m.°K For the same temperature drop and heat loss, this refractory wall can be replaced by a layer of diatomaceous earth of thermal conductivity 0.14 W/m.K and thickness ______________ metre?

   A. 0.01
   B. 0.1
   C. 0.25
   D. 0.5

2. The ratio of thermal & electrical conductivity is same for all the metals at the same temperature; and at around room temperature, this ratio is proportional to(where, T = absolute temperature, °K) ?

   A. T
   B. 1/T
   C. T2
   D. 1/T2

3. One face of a furnace wall is at 1030°C and the other face is exposed to room temperature (30°C). If the thermal conductivity of furnace wall is 3 W. m-1. k-1 and the wall thickness is 0.3 m, the maximum heat loss (in W/m) is____________________?

   A. 100
   B. 900
   C. 9000
   D. 10000

4. Which of the following commonly used condenser tube materials has the lowest thermal conductivity ?

   A. Admiralty brass
   B. Stainless steel
   C. Aluminium brass
   D. Titanium

5. Thermal conductivity of a material does not depend upon its_____________________?

   A. Mass
   B. Volume
   C. Surface area
   D. All A, C & C

6. What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m2. °K? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively ?

   A. 2
   B. 8
   C. 10
   D. 40

7. Temperature of hot gases flowing in a pipe is measured by a thermocouple inserted in the thermal well. The thermal well made of ______________ will facilitate the most accurate measurement of the temperature ?

   A. Copper
   B. Steel
   C. Aluminium
   D. Brass

8. Yield strength of a polycrystalline metal with an average grain size „d’, is proportional to ____________________?

   A. d1/2
   B. d-1/2
   C. d
   D. d-1

9. With increase in temperature, the electrical conductivity of a _________________ decreases ?

   A. Semi-conductor
   B. Metal or alloy
   C. Dielectric
   D. None of these

10. Which of the following materials has the poorest electrical conductivity ?

    A. Carbon
    B. Aluminium
    C. Silver
    D. Stainless steel