Download PDF
Free download in PDF Heat Transfer Short Questions and Answers for competitive exams. These short objective type questions with answers are very important for competitive exams like IIT-JEE, AIIMS, NEET etc. as well as Board exams. These short solved questions or quizzes are provided by Gkseries.
41
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
42
Planck’s law holds good for
[A]
Black Bodies
[B]
Polished Bodies
[C]
All Coloured Bodies
[D]
All Of The Above
43
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
Answer: does not vary with temperature and wave length of the incident ray
44
The time constant of a thermocouple is
[A]
the time taken to attain the final temperature to be measured
[B]
the time taken to attain 50% of the value of initial temperature difference
[C]
the time taken to attain 63.2% of the value of initial temperature difference
[D]
determined by the time taken to reach 100°C from 0°C
Answer: the time taken to attain 63.2% of the value of initial temperature difference
45
The concept of overall coefficient of heat transfer is used in heat transfer problems of
[A]
conduction
[B]
convection
[C]
radiation
[D]
conduction and comte_ction
Answer: conduction and comte_ction
46
In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by
[A]
hr (time)
[B]
sqm (area)
[C]
°C (temperature)
[D]
cm (thickness)
Answer: Planck’s constant
47
Thermal Conductivity Of Glass-Wool Varies From Sample To Sample Because Of Variation In
[A]
Composition
[B]
Density
[C]
Porosity
[D]
All Of The Above
48
Moisture would find its way into insulation by vapour pressure unless it is prevented by
[A]
high thickness of insulation
[B]
high vapour pressure
[C]
less thermal conductivity insulator
[D]
a vapour seal
49
Thermal diffusivity is
[A]
a dimensionless parameter
[B]
function of temperature
[C]
used as mathematical model
[D]
a physical property of the material
Answer: a physical property of the material
50
Thermal diffusivity of a substance is .
[A]
proportional of thermal conductivity
[B]
inversely proportional to k
[C]
proportional to (k)
[D]
inversely proportional to k2
Answer: proportional of thermal conductivity
51
Thermal Conductivity Of Wood Depends On
[A]
Moisture
[B]
Density
[C]
Temperature
[D]
All Of The Above
52
Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called
[A]
thermal resistance
[B]
thermal coefficient
[C]
temperature gradient
[D]
thermal conductivity
Answer: thermal conductivity
53
A grey body is one whose absorptivity
[A]
varies with temperature
[B]
varies with wavelength of the incident ray
[C]
is equal to its emissivity
[D]
does not vary with temperature and. wavelength of the incident ray
Answer: is equal to its emissivity
54
Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
[A]
1 :1
[B]
2: 1
[C]
1 : 2
[D]
4 : 1
55
In heat exchangers, degree of approach is defined as the difference between temperatures of
[A]
cold water inlet and outlet
[B]
hot medium inlet and outlet
[C]
hot medium outlet and cold water inlet
[D]
hot medium outlet and cold water outlet
Answer: hot medium outlet and cold water outlet
56
According of Kirchhoff’s law,
[A]
radiant heat is proportional to fourth power of absolute temperature
[B]
emissive power depends on temperature
[C]
emissive power and absorptivity are constant for all bodies
[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.
Answer: ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
57
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
58
The concept of overall coefficient of heat transfer is used in case of heat transfer by
[A]
conduction
[B]
convection
[C]
radiation
[D]
conduction and convection
Answer: conduction and convection
59
The value of Prandtl number for air is about
[A]
0.1
[B]
0.3
[C]
0.7
[D]
1.7
60
Log mean temperature difference in case of counter flow compared to parallel flow will be
[A]
same
[B]
more
[C]
less
[D]
depends on other factors
Please share this page