Choose the false statement

Thermal conductivity of dry material is lower than that of damp material

For pure metal thermal conductivity is more

Thermal conductivity decreases with increase in the density of the substance

Thermal conductivity of dry material is lower than that of damp material

Heat treatment causes variation in thermal conductivity

Most metals are good conductor of heat because of

Free electrons and frequent collision of atoms

Thermal conductivity is defined as the heat flow per unit time

When temperature gradient is unity

Across the wall with no temperature

Through a unit thickness of the wall

Across unit area where temperature gradient is unity

Negative sign in Fourier heat conduction equation indicates

Heat always flow is in the direction of positive temperature gradient

Heat always flow in the direction of negative temperature gradient

Here are some assumptions that are made for Fourier law. Identify the wrong one

Isotropic and homogenous material

Non- linear temperature profile

Isotropic and homogenous material

The relation Ϫ² t =0 is referred to as

Fourier heat conduction equation

Solution for transient conduction

The diffusion equationsɎ²t + q g = (1/α) (d t/d r)Governs the temperature distribution under unsteady heat flow through a homogenous and isotropic material. The Fourier equation follows from this expression when

Temperature doesn’t depends on time

There is no internal heat generation

Steady state conditions prevail

There is no internal heat generation but unsteady state condition prevails

37 + Mcqs in Fourier Equation And Thermal Conductivity in Heat Transfer Page 1 McqOptions

1.	What is the thermal conductivity of magnetite in W/m K?
A.	3.7
B.	3.8
C.	3.9
D.	4.0
Answer» C. 3.9

Discussion

2.	Heat conduction in gases is due to
A.	Elastic impact of molecules
B.	Movement of electrons
C.	EM Waves
D.	Mixing of gases
Answer» B. Movement of electrons

Discussion

3.	Which one is having lowest thermal conductivity?
A.	Furnace
B.	Wool
C.	Saw dust
D.	Glass wool
Answer» E.

Discussion

4.	Which one is having highest thermal conductivity?
A.	Silver
B.	Copper
C.	Glass
D.	Earth
Answer» B. Copper

Discussion

5.	The heat energy propagation due to conduction heat transfer will be minimum for
A.	Lead
B.	Water
C.	Air
D.	Copper
Answer» D. Copper

Discussion

6.	Cork is a good insulator because
A.	It is flexible
B.	It can be powdered
C.	Low density
D.	It is porous
Answer» E.

Discussion

7.	Choose the false statement
A.	For pure metal thermal conductivity is more
B.	Thermal conductivity decreases with increase in the density of the substance
C.	Thermal conductivity of dry material is lower than that of damp material
D.	Heat treatment causes variation in thermal conductivity
Answer» C. Thermal conductivity of dry material is lower than that of damp material

Discussion

8.	What is the thermal conductivity of ice in W/m K?
A.	1.55
B.	1.66
C.	1.77
D.	1.88
Answer» E.

Discussion

9.	What is the thermal conductivity of cotton in W/m K?
A.	0.03
B.	0.04
C.	0.05
D.	0.06
Answer» E.

Discussion

10.	What is the thermal conductivity of coal in W/m K?
A.	0.25
B.	0.26
C.	0.27
D.	0.28
Answer» C. 0.27

Discussion

11.	Most metals are good conductor of heat because of
A.	Transport of energy
B.	Free electrons and frequent collision of atoms
C.	Lattice defects
D.	Capacity to absorb energy
Answer» C. Lattice defects

Discussion

12.	What is the thermal conductivity of asphalt in W/m K?
A.	0.064
B.	0.063
C.	0.062
D.	0.061
Answer» D. 0.061

Discussion

13.	Mark the matter with least value of thermal conductivity
A.	Air
B.	Water
C.	Ash
D.	Window glass
Answer» B. Water

Discussion

14.	Which one of the following forms of water have the highest value of thermal conductivity?
A.	Boiling water
B.	Steam
C.	Solid ice
D.	Melting ice
Answer» D. Melting ice

Discussion

15.	The average thermal conductivities of water and air conform to the ratio
A.	50:1
B.	25:1
C.	5:1
D.	15:1
Answer» C. 5:1

Discussion

16.	Identify the very good insulator
A.	Saw dust
B.	Cork
C.	Asbestos sheet
D.	Glass wool
Answer» E.

Discussion

17.	“Thermal conductivity represents the amount of heat conducted across unit area when a temperature difference of one kelvin”. True or false
A.	True
B.	False
C.	May be
D.	Can't say
Answer» C. May be

Discussion

18.	Which of the following is the unit of thermal resistance?
A.	degree/kcal
B.	hour degree
C.	s degree/kcal
D.	degree/W
Answer» E.

Discussion

19.	Transmission of heat i.e. molecular is smallest in case of
A.	Gases
B.	Liquids
C.	Alloys
D.	Solids
Answer» B. Liquids

Discussion

20.	Thermal conductivity is defined as the heat flow per unit time
A.	When temperature gradient is unity
B.	Across the wall with no temperature
C.	Through a unit thickness of the wall
D.	Across unit area where temperature gradient is unity
Answer» E.

Discussion

21.	Which one is not the unit of thermal conductivity?
A.	kcal/m hr K
B.	KJ/m hr K
C.	W/m s K
D.	Cal/cm s K
Answer» D. Cal/cm s K

Discussion

22.	What is the thermal conductivity of apple in W/m K?
A.	0.513
B.	0.613
C.	0.713
D.	0.813
Answer» B. 0.613

Discussion

23.	Consider the following statements:The Fourier heat conduction equationQ = -k A d t /d xPresumesi) Steady state conditionsii) Constant value of thermal conductivityiii) Uniform temperature at the wall surfaceiv) One dimensional heat flowWhich of these statements are correct?
A.	1, 2 and 3
B.	1, 2 and 4
C.	2, 3 and 4
D.	1, 3 and 4
Answer» E.

Discussion

24.	The famous Fourier series is named after
A.	Diller and Ryan
B.	J.B. Joseph Fourier
C.	Stefan- Boltzmann
D.	Wein’s
Answer» C. Stefan- Boltzmann

Discussion

25.	Negative sign in Fourier heat conduction equation indicates
A.	Heat always flow is in the direction of positive temperature gradient
B.	Heat always flow in the direction of negative temperature gradient
C.	No heat flow is there
D.	Data is insufficient
Answer» C. No heat flow is there

Discussion

26.	Fourier law of heat conduction is best represented by
A.	Q = -k A d t /d x
B.	Q = k A d x/d t
C.	Q = -k A
D.	Q = k d t/d x
Answer» B. Q = k A d x/d t

Discussion

27.	Here are some assumptions that are made for Fourier law. Identify the wrong one
A.	No internal heat generation
B.	Steady state heat conduction
C.	Non- linear temperature profile
D.	Isotropic and homogenous material
Answer» D. Isotropic and homogenous material

Discussion

28.	The thermal conductivity and the electrical conductivity of a metal at absolute temperature are related as
A.	k/σ T
B.	k/σ
C.	k σ/T
D.	k/T
Answer» B. k/σ

Discussion

29.	The relation Ϫ² t =0 is referred to as
A.	Poisson’s equation
B.	Fourier heat conduction equation
C.	Solution for transient conduction
D.	Laplace equation
Answer» E.

Discussion

30.	The unit of thermal diffusivity is
A.	m²/hr-K
B.	kcal/m²-hr
C.	m²/hr
D.	m/hr-K
Answer» D. m/hr-K

Discussion

31.	To effect a bond between two metal plates, 2.5 cm and 15 cm thick, heat is uniformly applied through the thinner plate by a radiant heat source. The bonding must be held at 320 K for a short time. When the heat source is adjusted to have a steady value of 43.5 k W/m², a thermocouple installed on the side of the thinner plate next to source indicates a temperature of 345 K. Calculate the temperature gradient for heat conduction through thinner plate. In the diagram, the upper plate is 2.5 cm thick while the lower is 15 cm thick.
A.	– 1000 degree Celsius/m
B.	– 2000 degree Celsius/m
C.	– 3000 degree Celsius/m
D.	– 4000 degree Celsius/m
Answer» B. – 2000 degree Celsius/m

Discussion

32.	The diffusion equationsɎ²t + q g = (1/α) (d t/d r)Governs the temperature distribution under unsteady heat flow through a homogenous and isotropic material. The Fourier equation follows from this expression when
A.	Temperature doesn’t depends on time
B.	There is no internal heat generation
C.	Steady state conditions prevail
D.	There is no internal heat generation but unsteady state condition prevails
Answer» E.

Discussion

33.	Consider the following parameters(i) Composition(ii) Density(iii) Porosity(iv) StructureThen, thermal conductivity of glass wool varies from sample to sample because of variation is
A.	1 and 2
B.	1, 2, 3 and 4
C.	1 and 3
D.	1, 2 and 3
Answer» C. 1 and 3

Discussion

34.	Low temperature insulation are used when the enclosure is at a temperature lower than the ambient temperature. Which one of the following is not a low temperature insulation?
A.	Asbestos
B.	Cork
C.	Cattle hair
D.	Slag wool
Answer» B. Cork

Discussion

35.	The diagram shows heat conduction through a plane wall. The surface temperature is 475 K and it radiates heat to the surroundings at 335 K. If thermal conductivity of the material is 12.5 W/m degree, find the temperature gradient. Let convective coefficient be 80 W/m² degree and radiation factor is 0.9
A.	– 1052.4 degree celsius
B.	– 2052.4 degree celsius
C.	– 3052.4 degree celsius
D.	– 4052.4 degree celsius
Answer» B. – 2052.4 degree celsius

Discussion

36.	From the concept of kinetic theory, mean travel velocity of the gas molecules is prescribed by the relation(Where,G = Universal gas constantM = Molecular weight of the gasT = Absolute temperature)
A.	V = (3M/GT)⅟₂
B.	V = (3GT/M)⅟₂
C.	V = (6T/GM)⅟₂
D.	V = (3GT/2M)⅟₂
Answer» C. V = (6T/GM)⅟₂

Discussion

37.	The value of Lorenz number in 10¯⁸ W ohms/K² is
A.	2.02
B.	2.35
C.	2.56
D.	2.45
Answer» E.

Discussion

Explore topic-wise MCQs in Heat Transfer.

What is the thermal conductivity of magnetite in W/m K?

Heat conduction in gases is due to

Which one is having lowest thermal conductivity?

Which one is having highest thermal conductivity?

The heat energy propagation due to conduction heat transfer will be minimum for

Cork is a good insulator because

Choose the false statement

What is the thermal conductivity of ice in W/m K?

What is the thermal conductivity of cotton in W/m K?

What is the thermal conductivity of coal in W/m K?

Most metals are good conductor of heat because of

What is the thermal conductivity of asphalt in W/m K?

Mark the matter with least value of thermal conductivity

Which one of the following forms of water have the highest value of thermal conductivity?

The average thermal conductivities of water and air conform to the ratio

Identify the very good insulator

“Thermal conductivity represents the amount of heat conducted across unit area when a temperature difference of one kelvin”. True or false

Which of the following is the unit of thermal resistance?

Transmission of heat i.e. molecular is smallest in case of

Thermal conductivity is defined as the heat flow per unit time

Which one is not the unit of thermal conductivity?

What is the thermal conductivity of apple in W/m K?

Consider the following statements:The Fourier heat conduction equationQ = -k A d t /d xPresumesi) Steady state conditionsii) Constant value of thermal conductivityiii) Uniform temperature at the wall surfaceiv) One dimensional heat flowWhich of these statements are correct?

The famous Fourier series is named after

Negative sign in Fourier heat conduction equation indicates

Fourier law of heat conduction is best represented by

Here are some assumptions that are made for Fourier law. Identify the wrong one

The thermal conductivity and the electrical conductivity of a metal at absolute temperature are related as

The relation Ϫ² t =0 is referred to as

The unit of thermal diffusivity is

The diffusion equationsɎ²t + q g = (1/α) (d t/d r)Governs the temperature distribution under unsteady heat flow through a homogenous and isotropic material. The Fourier equation follows from this expression when

Consider the following parameters(i) Composition(ii) Density(iii) Porosity(iv) StructureThen, thermal conductivity of glass wool varies from sample to sample because of variation is

Low temperature insulation are used when the enclosure is at a temperature lower than the ambient temperature. Which one of the following is not a low temperature insulation?

From the concept of kinetic theory, mean travel velocity of the gas molecules is prescribed by the relation(Where,G = Universal gas constantM = Molecular weight of the gasT = Absolute temperature)

The value of Lorenz number in 10¯⁸ W ohms/K² is