Heat MCQs | Heat Short Questions(MCQs) & Answers

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Questions
41 According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
A grey body
B brilliant white polished body
C red hot body
D black body

Answer: black body
42 The unit of overall coefficient of heat transfer is
A kcal/m2
B kcal/hr °C
C kcal/m2 hr °C
D kacl/m hr °C

Answer: kcal/m2 hr °C
43 Joule sec is the unit of
A universal gas constant
B kinematic viscosity
C thermal conductivity
D Planck's constant

Answer: Planck's constant
44 The value of Prandtl number for air is about
A 0.1
B 0.3
C 0.7
D 1.7

Answer: 0.7
45 Total emissivity of polished silver compared to black body is
A same
B higher
C more or less same
D very much lower

Answer: very much lower
46 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

Answer: fourth power of absolute temperature
47 The unit of Stefan Boltzmann constant is
A watt/cm2 °K
B watt/cm4 °K
C watt2/cm °K4
D watt/cm2 °K4

Answer: watt/cm2 °K4
48 In free con-vection heat transfer, Nusselt number is function of
A Grashoff no. and Reynold no.
B Grashoff no. and Prandtl no.
C Prandtl no. and Reynold no.
D Grashoff no., Prandtl no. and Reynold no.

Answer: Grashoff no. and Prandtl no.
49 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

Answer: more than those for liquids
50 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 the above

Answer: all of the above
51 Depending on the radiating properties, a body will be white when
A p = 0, x = 0 and a = 1
B p=l,T = 0anda = 0
C p = 0, x = 1 and a = 0
D x = 0, a + p = 1

Answer: p=l,T = 0anda = 0
52 Depending on the radiating properties, a body will be opaque when
A p = 0, x = 0 and a = 1
B p = 0, x = 1 and a = 0
C x - 0, a + p = 1
D a=0,x + p= 1

Answer: x - 0, a + p = 1
53 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

Answer: time
54 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

Answer: absorptive power
55 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

Answer: all of the above
56 The emissive power of a body depends upon its
A temperature
B wave length
C physical nature
D all of the above

Answer: all of the above
57 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

Answer: when system is under thermal equi-librium
58 Planck's law holds good for
A black bodies
B polished bodies
C all coloured bodies
D all of the above

Answer: black bodies
59 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 81

Answer: 81
60 Depending on the radiating properties, body will be transparent when
A p = 0, x = 0 and a = 1
B p=l,x = 0,anda = 0
C p = 0, T= l,anda = 0
D X = 0, a + p = 1

Answer: p = 0, T= l,anda = 0

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