Question: Stefan Boltzmann law is applicable for heat transfer by __________________?

• 1. conduction
• 2. convection
• 3. radiation
• 4. conduction and radiation combined

Question: Thermal diffusivity of a substance is __________________?

• 1. directly proportional to thermal con¬ductivity
• 2. inversely proportional to density of substance
• 3. inversely proportional to specific heat
• 4. all of the above

Question: The thermal diffusivities for gases are generally_____________________?

• 1. more than those for liquids
• 2. less than those for liquids
• 3. more than those for solids
• 4. dependent on the viscosity

Question: A grey body is one whose absorptivity _________________?

• 1. varies with temperature
• 2. varies with the wave length of incident ray
• 3. varies with both
• 4. does not vary with temperature and wave length of the incident ray

Question: Planck’s law holds good for________________?

• 1. black bodies
• 2. polished bodies
• 3. all coloured bodies
• 4. all of the above

Question: A perfect black body is one which_______________?

• 1. is black in colour
• 2. reflects all heat
• 3. transmits all heat radiations
• 4. abslprbs heat radiations of all wave lengths falling on it

Question: If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of___________________?

• 1. 3
• 2. 6
• 3. 9
• 4. 81

Question: In regenerator type heat exchanger, heat transfer takes place by___________________?

• 1. direct mixing of hot and cold fluids
• 2. a complete separation between hot and cold fluids
• 3. flow of hot and cold fluids alternately over a surface
• 4. generation of heat again and again

Question: Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by ___________________?

• 1. convection
• 2. free convection
• 3. forced convection
• 4. radiation

Question: Depending on the radiating properties, body will be transparent when________________?

• 1. p = 0, x = 0 and a = 1
• 2. p=l,x = 0,anda = 0
• 3. p = 0, T= l,anda = 0
• 4. X = 0, a + p = 1