heat transfer objective questions with answers part3

Q1. Total emissivity of polished silver compared to black body is
(A) same
(B) higher
(C) more or less same
(D) very much lower

Q2. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
(A) absolute temperature
(B) square of temperature
(C) fourth power of absolute temperature
(D) fourth power of temperature

Q3. Which of the following property of air does not increase with rise in temperature
(A) thermal conductivity
(B) thermal diffusivity
(C) density
(D) dynamic viscosity

Q4. In free con-vection heat transfer, Nusselt number is function of
(A) Grashoff number and Reynold number
(B) Grashoff number and Prandtl number
(C) Prandtl number and Reynold number
(D) Grashoff number, Prandtl number and Reynold number

Q5. Stefan Boltzmann law is applicable for heat transfer by
(A) conduction
(B) convection
(C) radiation
(D) conduction and radiation combined

Q6. 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

Q7. The thermal diffusivities for solids are generally
(A) less than those for gases
(B) jess than those for liquids
(C) more than those for liquids and gases
(D) more or less same as for liquids and gases

Q8. 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 these

Q9. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
(A) Krichoff’s law
(B) Stefan’s law
(C) Wien’ law
(D) Planck’s law

Q10. According to Wien’s law, the wavelength corresponding to maximum emission is proportional to
(A) absolute temperature (T)
(B) f
(C) t
(D) inverse of absolute temperature (T)

Q11. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
(A) temperature
(B) thickness
(C) area
(D) time

Q12. 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

Q13. he amount of radiation mainly depends on
(A) nature of body
(B) temperature of body
(C) type of surface of body
(D) All of these

Q14. The emissive power of a body depends upon its
(A) temperature
(B) wave length
(C) physical nature
(D) All of these

Q15. 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

Q16. 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

Q17. 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

Q18. 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

Q19. Planck’s law holds good for
(A) black bodies
(B) polished bodies
(C) all coloured bodies
(D) All of these

Q20. 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