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1.

40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is                        
A. 0.45 B. 0.55
C. 0.4 D. 0.75



2.

A grey body is one whose absorptivity                        
A. varies with temperature B. varies with wavelength of the incident ray
C. is equal to its emissivity D. does not vary with temperature and. wavelength of the incident ray



3.

A non-dimensional number generally associated with natural convection heat transfer is                        
A. Grashoff number B. Nusselt number
C. Weber number D. Prandtl number




4.

A steam pipe is to be insulated by two insulating materials put over each other. For best results                        
A. better insulation should be put over pipe and better one over it B. inferior insulation should be put over pipe and better one over it
C. both may be put in any order D. whether to put inferior OIL over pipe or the better one would depend on steam temperature



5.

Absorptivity of a body will be equal to its emissivity                        
A. at all temperatures B. at one particular temperature
C. when system is under thermal equiplibrium D. at critical temperature



6.

According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a                        
A. grey body B. brilliant white polished body
C. red hot body D. black body



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