Which of the following materials has the poorest electrical 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. With increase in temperature, the electrical conductivity of a _________________ decreases ?

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

3. 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

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. The transition temperature at which all the ferromagnetic materials become paramagnetic materials is termed as the ‘Curie temperature’. Its value for cobalt is ______________ °C?

   A. 768
   B. 1127
   C. 1359
   D. 1480

6. 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

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

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

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

   A. 1/k
   B. k
   C. k2
   D. 1/k2

9. 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

10. Resistance of an electrical conductor is proportional to its (where, l = length and A = crosssectional area of the conductor)________________?

    A. A
    B. l
    C. A2
    D. Both A. & B.