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. 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

3. Radiant energy received by a body is proportional to (where, d = the distance between the object emitting radiation and that receiving it.) ?

   A. √d
   B. d
   C. d2
   D. d1.5

4. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is______________?

   A. 1.66
   B. 88.66
   C. 3.66
   D. Dependent on NRe only

5. 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

6. 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

7. For a perfectly transparent surface (like gases), the____________________?

   A. Absorptivity = 0
   B. Transmissivity = 1
   C. Reflectivity = 0
   D. All A., B. & C.

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. 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

10. What is the emissivity of a black body ?

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