A. 0.35
B. 0.45
C. 0.55
D. 0.85
Related Mcqs:
- 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 - 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 - 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 - 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 - 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 - 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 - For a perfectly transparent surface (like gases), the____________________?
A. Absorptivity = 0
B. Transmissivity = 1
C. Reflectivity = 0
D. All A., B. & C. - A _____________ surface has the maximum thermal emissivity out of the following ?
A. Black & smooth
B. Black & rough
C. White & smooth
D. White & rough - 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 - What is the emissivity of a black body ?
A. 0
B. 1
C. 0.5
D. 0.90
