Questions and answers for exam Preparation

MCQs

Total Questions : 448 | Page 9 of 45 pages

Question 81. Joule sec is the unit of

Universal gas constant
Kinematic viscosity
Thermal conductivity
Planck's constant

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Answer: Option D. -> Planck's constant

Question 82. 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

Wien's law
Stefan's law
Kirchhoff's law
Planck's law

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Answer: Option C. -> Kirchhoff's law

Question 83. Which of the following statement is correct?

A grey body is one which absorbs all radiations incident on it.
At thermal equilibrium, the emissivity and absorptivity are same.
The energy absorbed by a body to the total energy falling on it, is called emissivity.
A perfect body is one which is black in colour.

Discuss Question

Answer: Option B. -> At thermal equilibrium, the emissivity and absorptivity are same.

Question 84. In free convection heat transfer, Nusselt number is function of

Grashoff number and Reynold number
Grashoff number and Prandtl number
Prandtl number and Reynold number
Grashoff number, Prandtl number and Reynold number

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Answer: Option B. -> Grashoff number and Prandtl number

Question 85. In regenerator type heat exchanger, heat transfer takes place by

Direct mixing of hot and cold fluids
A complete separation between hot and cold fluids
Flow of hot and cold fluids alternately over a surface
Generation of heat again and again

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Answer: Option C. -> Flow of hot and cold fluids alternately over a surface

Question 86. Heat flows from one body to other when they have

Different heat contents
Different specific heat
Different atomic structure
Different temperatures

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Answer: Option D. -> Different temperatures

Question 87. Which of the following would lead to a reduction in thermal resistance?

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
In convection, stirring of the fluid and cleaning the heating surface.
In radiation, increasing the temperature and reducing the emissivity.
All of the above

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Answer: Option D. -> All of the above

Question 88. The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to

-1/3
-2/3
1
-1

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Answer: Option A. -> -1/3

Question 89. Heat transfer in liquid and gases takes place by

Conduction
Convection
Radiation
Conduction and convection

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Answer: Option B. -> Convection

Question 90. According of Kirchhoff's law

Radiant heat is proportional to fourth power of absolute temperature
Emissive power depends on temperature
Emissive power and absorptivity are constant for all bodies
Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

Discuss Question

Answer: Option D. -> Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body