With increase in temperature, the total emissivity of conductors____________________?

Related Mcqs:

1. The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m2. The approximate surface temperature (K) is (Stefan-Boltzmann constant = 5.67 × 10-8 W/m2.K4) ?

   A. 1000
   B. 727
   C. 800
   D. 1200

2. While the total emissivity of a perfect black body is unity, the same for a real body is__________________?

   A. 0
   B. 1
   C. > 1
   D. Between 0 and 1

3. The absorptivity of a body is equal to its emissivity _________________?

   A. At a particular temperature
   B. For circular bodies
   C. Under thermal equilibrium
   D. None of these

4. What is the emissivity of a black body ?

   A. 0
   B. 1
   C. 0.5
   D. 0.90

5. A body is called grey if the monochromatic emissivity of the body is___________________?

   A. Zero
   B. Unity
   C. Same for all wavelengths
   D. Different for all wavelengths

6. Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be_________________?

   A. 0.35
   B. 0.45
   C. 0.55
   D. 0.85

7. The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by__________________?

   A. Painting the surface black
   B. Painting the surface white (with aluminium paint)
   C. Giving the surface a mirror finish
   D. Roughening the surface

8. A _____________ surface has the maximum thermal emissivity out of the following ?

   A. Black & smooth
   B. Black & rough
   C. White & smooth
   D. White & rough

9. If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows ____________ law?

   A. Hyperbolic
   B. Parabolic
   C. Linear
   D. Logarithmic

10. A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time ___________________?

    A. t = 283 s
    B. t = 356 s
    C. t = 400 s
    D. t = 800 s