The value of Prandtl number for air is about _______________________?
(A) 0.1
(B) 0.3
(C) 0.7
(D) 1.7
(D) 10.5
The ratio of the energy absorbed by the body to total energy falling on it is called_________________?
(A) absorptive power
(B) emissive power
(C) absorptivity
(D) emissivity
(D) none of the above
The amount of radiation mainly depends on___________________?
(A) nature of body
(B) temperature of body
(C) type of surface of body
(D) all of the above
(D) none of the above
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 equi-librium
(D) at critical temperature
(D) for a polished body
Depending on the radiating properties, body will be transparent when________________?
(A) p = 0, x = 0 and a = 1
(B) p=l,x = 0,anda = 0
(C) p = 0, T= l,anda = 0
(D) X = 0, a + p = 1
(D) a = 0,x + p= 1
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by ___________________?
(A) convection
(B) free convection
(C) forced convection
(D) radiation
(D) radiation and convection
In regenerator type heat exchanger, heat transfer takes place by___________________?
(A) direct mixing of hot and cold fluids
(B) a complete separation between hot and cold fluids
(C) flow of hot and cold fluids alternately over a surface
(D) generation of heat again and again
(D) indirect transfer
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of___________________?
(A) 3
(B) 6
(C) 9
(D) 27
(D) 81
A perfect black body is one which_______________?
(A) is black in colour
(B) reflects all heat
(C) transmits all heat radiations
(D) abslprbs heat radiations of all wave lengths falling on it
(D) fully opaque
Planck’s law holds good for________________?
(A) black bodies
(B) polished bodies
(C) all coloured bodies
(D) all of the above
(D) none of the above