91. 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
(e) area and time.
Ans: d
92. 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
(e) none of the above.
Ans: a
93. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
(a) 0.45
(b) 0.55
(c) 0.40
(d) 0.75
(e) 0.60.
Ans: a
94. The amount of radiation mainly depends on
(a) nature of body
(b) temperature of body
(c) type of surface of body
(d) all of the above
(e) none of the above.
Ans: d
95. The emissive power of a body depends upon its
(a) temperature
(b) wave length
(c) physical nature
(d) all of the above
(e) none of the above.
Ans: d
96. Two 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
(e) radiation and convection.
Ans: d
97. 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 equiplibrium
(d) at critical temperature
(e) for a polished body.
Ans: c
98. In re generator 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
(e) indirect transfer.
Ans: c
99. 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
(e) fully opaque.
Ans: d
100. Planck's law holds good for
(a) black bodies
(b) polished bodies
(c) all colored bodies
(d) all of the above
(e) none of the above.
Ans: a
101. If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
(a) 3
(b) 6
(c) 9
(d) 27
(e) 81.
Ans: e
102. Depending on the radiating properties, body will be transparent when
(a) p = 0, x = 0 and a = 1
(b) p=l,x = 0, and a = 0
(c) p = 0, T= l, and a = 0
(d) X = 0, a + p = 1
(e) a = 0,x + p= 1.
Ans: c
103. 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
(e) there is no such criterion.
Ans: d
Read More Questions:
Heat Transfer - Mechanical MCQs Part1
Heat Transfer - Mechanical MCQs Part2
(a) temperature
(b) thickness
(c) area
(d) time
(e) area and time.
Ans: d
92. 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
(e) none of the above.
Ans: a
93. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
(a) 0.45
(b) 0.55
(c) 0.40
(d) 0.75
(e) 0.60.
Ans: a
94. The amount of radiation mainly depends on
(a) nature of body
(b) temperature of body
(c) type of surface of body
(d) all of the above
(e) none of the above.
Ans: d
95. The emissive power of a body depends upon its
(a) temperature
(b) wave length
(c) physical nature
(d) all of the above
(e) none of the above.
Ans: d
96. Two 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
(e) radiation and convection.
Ans: d
97. 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 equiplibrium
(d) at critical temperature
(e) for a polished body.
Ans: c
98. In re generator 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
(e) indirect transfer.
Ans: c
99. 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
(e) fully opaque.
Ans: d
100. Planck's law holds good for
(a) black bodies
(b) polished bodies
(c) all colored bodies
(d) all of the above
(e) none of the above.
Ans: a
101. If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
(a) 3
(b) 6
(c) 9
(d) 27
(e) 81.
Ans: e
102. Depending on the radiating properties, body will be transparent when
(a) p = 0, x = 0 and a = 1
(b) p=l,x = 0, and a = 0
(c) p = 0, T= l, and a = 0
(d) X = 0, a + p = 1
(e) a = 0,x + p= 1.
Ans: c
103. 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
(e) there is no such criterion.
Ans: d
Read More Questions:
Heat Transfer - Mechanical MCQs Part1
Heat Transfer - Mechanical MCQs Part2
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