The unit of Stefan Boltzmann constant is ____________________?

A. Watt/cm2 °k
B. Watt/cm4 °k
C. Watt2/cm °k4
D. Watt/cm2 °k4

Stefan Boltzmann law is applicable for heat transfer by __________________?

A. Conduction
B. Convection
C. Radiation
D. Conduction and radiation combined

Thermal diffusivity of a substance is __________________?

A. Directly proportional to thermal con¬ductivity
B. Inversely proportional to density of substance
C. Inversely proportional to specific heat
D. All of the above

The thermal diffusivities for gases are generally_____________________?

A. More than those for liquids
B. Less than those for liquids
C. More than those for solids
D. Dependent on the viscosity

A grey body is one whose absorptivity _________________?

A. Varies with temperature
B. Varies with the wave length of incident ray
C. Varies with both
D. Does not vary with temperature and wave length of the incident ray

Planck’s law holds good for________________?

A. Black bodies
B. Polished bodies
C. All coloured bodies
D. All of the above

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

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

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

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