Heat transfer MCQ with Answers

71) Stefan Boltzmann law is applicable for heat transfer by

Answer is:

radiation

Explanation:

Stefan Boltzmann law is applicable for heat transfer by radiation. According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature.

72) The thermal diffusivities for gases are generally

Answer is:

more than those for liquids

73) The thermal diffusivities for solids are generally

Answer is:

more than those for liquids and gases

74) Thermal diffusivity of a substance is

Answer is:

all of the above

Explanation:

Thermal diffusivity of a substance is
* directly proportional to the thermal conductivity
* inversely proportional to density of substance
* inversely proportional to specific heat

75) 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

Answer is:

71) Stefan Boltzmann law is applicable for heat transfer by

radiation

72) The thermal diffusivities for gases are generally

more than those for liquids

73) The thermal diffusivities for solids are generally

more than those for liquids and gases

74) Thermal diffusivity of a substance is

all of the above

75) 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

Krichoff′s law