does not vary with temperature and. wavelength of the incident ray
none of the above.
Correct answer: (C) is equal to its emissivity
2. non-dimensional number generally associated with natural convection heat transfer is
Grashoff number
Nusselt number
Weber number
Prandtl number
Reynold number.
Correct answer: (A) Grashoff number
3. perfect black body is one which
is black in colour
reflects all heat
transmits all heat radiations
abslprbs heat radiations of all wave lengths falling on it
fully opaque.
Correct answer: (D) abslprbs heat radiations of all wave lengths falling on it
4. steam pipe is to be insulated by two insulating materials put over each other. For best results
better insulation should be put over pipe and better one over it
inferior insulation should be put over pipe and better one over it
both may be put in any order
whether to put inferior OIL over pipe or the better one would depend on steam temperature
unpredictable.
Correct answer: (A) better insulation should be put over pipe and better one over it
5. Thermal conductivity of glass-wool varies from sample to sample because of variation in
composition
density
porosity
structure
all of the above.
Correct answer: (E) all of the above.
6. 0% 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
0.45
0.55
0.4
0.75
0.60.
Correct answer: (A) 0.45
7. A grey body is one whose absorptivity
varies with temperature
varies with the wave length of incident ray
varies with both
does not vary with temperature and wave length of the incident ray
there is no such criterion.
Correct answer: (D) does not vary with temperature and wave length of the incident ray
8. According to Prevost theory of heat exchange
it is impossible to transfer heat from low temperature source to t high temperature source
heat transfer by radiation requires no medium
all bodies above absolute zero emit radiation
heat transfer in most of the cases takes place by combination of conduction, convection and radiation
rate of heat transfer depends on thermal conductivity and temperature difference.
Correct answer: (C) all bodies above absolute zero emit radiation
9. bsorptivity of a body will be equal to its emissivity
at all temperatures
at one particular temperature
when system is under thermal equi-librium
at critical temperature
for a polished body.
Correct answer: (C) when system is under thermal equi-librium
10. ccording of Kirchhoff's law,
radiant heat is proportional to fourth power of absolute temperature
emissive power depends on temperature
emissive power and absorptivity are constant for all bodies
ratio of emissive power to absorptive power is maximum for perfectly black body
ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
Correct answer: (E) ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.