Heat And Mass Transfer(Mechanical Engineering ) Questions and Answers

Question 1. All radiations in a black body are
  1.    Reflected
  2.    Refracted
  3.    Transmitted
  4.    Absorbed
Explanation:-
Answer: Option D. -> Absorbed
an object that absorbs all radiation falling on it, at all wavelengths, is called a black body.
When a black body is at a uniform temperature, its emission has a characteristic frequency distribution that depends on the temperature.
Its emission is called black-body radiation.
Question 2. The heat is transferred by conduction, convection and radiation in
  1.    Melting of ice
  2.    Boiler furnaces
  3.    Condensation of steam in condenser
  4.    None of these
Explanation:-
Answer: Option B. -> Boiler furnaces
The heat is transferred by conduction, convection and radiation in Boiler Furnaces
Question 3. The amount of heat flow through a body by conduction is
  1.    Directly proportional to the surface area of the body
  2.    Directly proportional to the temperature difference on the two faces of the body
  3.    Dependent upon the material of the body
  4.    All of the above
Explanation:-
Answer: Option D. -> All of the above
The amount of heat flow through a body by conduction is
- Directly proportional to the surface area of the body
- Directly proportional to the temperature difference on the two faces of the body
- Dependent upon the material of the body
Question 4. Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in
  1.    Electric heater
  2.    Steam condenser
  3.    Boiler
  4.    Refrigerator condenser coils
Explanation:-
Answer: Option C. -> Boiler
Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in Boiler
Question 5. The radiation emitted by a black body is known as
  1.    Black radiation
  2.    Full radiation
  3.    Total radiation
  4.    All of these
Explanation:-
Answer: Option D. -> All of these
When a black body is at a uniform temperature, its emission has a characteristic frequency distribution that depends on the temperature. Its emission is called black-body radiation
Question 6. According of Kirchhoff's law
  1.    Radiant heat is proportional to fourth power of absolute temperature
  2.    Emissive power depends on temperature
  3.    Emissive power and absorptivity are constant for all bodies
  4.    Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body
Explanation:-
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
Kirchhoff's law states that the emissivity and the absorptivity of a surface at a given temperature and wavelength are equal.
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 Kirchhoff's law
Question 7. Thermal conductivity of wood depends on
  1.    Moisture
  2.    Density
  3.    Temperature
  4.    All of the above
Explanation:-
Answer: Option D. -> All of the above
Thermal conductivity is a material property. It will not differ with the dimensions of a material, but it is dependent on the temperature, the density and the moisture content of the material. The thermal conductivity of a material depends on its temperature, density and moisture content.
Question 8. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
  1.    Emissivity
  2.    Transmissivity
  3.    Reflectivity
  4.    Intensity of radiation
Explanation:-
Answer: Option D. -> Intensity of radiation
The intensity of radiation is defined as the rate of emission of radiation in a given direction from a surface per unit solid angle and per unit projected area of a radiating surface on a plane perpendicular to the direction of radiation.
Question 9. The ratio of the energy absorbed by the body to total energy falling on it is called
  1.    Absorptive power
  2.    Emissive power
  3.    Absorptivity
  4.    Emissivity
Explanation:-
Answer: Option A. -> Absorptive power
Absorptive power is a measure of heat absorbed by an object. When heat is incident on the surface an object, a part of it is absorbed and the remaining part is reflected. Usually the absorbed radiation is converted to thermal energy, increasing the object's temperature.
Question 10. Which of the following is the case of heat transfer by radiation?
  1.    Blast furnace
  2.    Heating of building
  3.    Cooling of parts in furnace
  4.    Heat received by a person from fireplace
Explanation:-
Answer: Option D. -> Heat received by a person from fireplace
Radiation refers to the emission of energy in rays or waves. Heat moves through space as energy waves. It is the type of heat one feels when sitting in front of a fireplace or around a campfire.
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