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Free download in PDF Heat Short Questions & Answers for competitive exams. These objective type questions are very important for competitive exams like IIT-JEE, NEET, AIIMS, JIPMER etc. These short solved questions or quizzes are provided by Gkseries.
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
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
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
45
Total emissivity of polished silver compared to black body is
[A]
same
[B]
higher
[C]
more or less same
[D]
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
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
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
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
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
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
56
The emissive power of a body depends upon its
[A]
temperature
[B]
wave length
[C]
physical nature
[D]
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
59
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of
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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