Practice Heat And Mass Transfer Multiple Choice Questions Quiz-2

Q.1

The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

Equal to
Directly proportional to
Inversely proportional to
None of these

Q.2

The use of heat exchangers is made in

Radiators in automobile
Condensers and boilers in steam plants
Condensers and evaporators in refrigeration and air conditioning units
All of the above

Q.3

The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

First law of thermodynamics
Newton's law of cooling
Newton's law of heating
Stefan's law

Q.4

Which of the following statement is wrong?

The heat transfer in liquid and gases takes place according to convection
The amount of heat flow through a body is dependent upon the material of the body
The thermal conductivity of solid metals increases with rise in temperature
Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference

Q.5

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

α = 1, ρ = 0 and τ = 0
α = 0, ρ = 1 and τ = 0
α = 0, ρ = 0 and τ = 1
α + ρ = 1 and τ = 0

Q.6

Planck’s law holds good for

black bodies
polished bodies
all coloured bodies
all of the above

Q.7

Thermal conductivity of a material may be defined as the

Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C
Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
All of the above

Q.8

A perfect black body is one which

Is black in colour
Reflects all heat
Transmits all heat radiations
Absorbs heat radiations of all wave lengths falling on it

Q.9

Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called

Thermal resistance
Thermal coefficient
Temperature gradient
Thermal conductivity

Q.10

The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as

Thermal coefficient
Thermal resistance
Thermal conductivity
None of these

Q.11

Depending on the radiating properties, a body will be white when
(Where a = absorptivity, p = reflectivity, x = transmissivity)

P = 0, x = 0 and a = 1
P=1, T = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 1

Q.12

In heat transfer, conductance equals conductivity (kcal/hr/sq.m/°C/cm) divided by

Hr (time)
Sq. m (area)
°C (temperature)
K.cal (heat)

Q.13

Depending on the radiating properties, body will be transparent when
(Where a = absorptivity, p = reflectivity, x = transmissivity)

P = 0, x = 0 and a = 1
P=1, x = 0, and a = 0
P = 0, x= 1, and a = 0
X = 0, a + p = 1

Q.14

The expression Q = ρ AT4 is called

Fourier equation
Stefan-Boltzmann equation
Newton Reichmann equation
Joseph-Stefan equation

Q.15

The time constant of a thermocouple is

The time taken to attain the final temperature to be measured
The time taken to attain 50% of the value of initial temperature difference
The time taken to attain 63.2% of the value of initial temperature difference
Determined by the time taken to reach 100°C from 0°C

Q.16

The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit

Temperature
Thickness
Area
Time

Q.17

Heat transfer takes place as per

Zeroth law of thermodynamics
First law of thermodynamic
Second law of the thermodynamics
Kirchoff's law

Q.18

Thermal diffusivity is

A dimensionless parameter
Function of temperature
Used as mathematical model
A physical property of the material

Q.19

Conduction is a process of heat transfer

From one particle of the body to another without the actual motion of the particles
From one particle of the body to another by the actual motion of the heated particles
From a hot body to a cold body, in a straight line, without affecting the intervening medium
None of the above

Q.20

According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

Pb = pa - pv
Pb = pa + pv
Pb = pa × pv
Pb = pa/pv

Q.21

A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

k₁ k₂
(k₁ + k₂)
(k₁ + k₂)/ k₁ k₂
2 k₁ k₂/ (k₁ + k₂)

Q.22

Total emissivity of polished silver compared to black body is

Same
Higher
More or less same
Very much lower

Q.23

Depending on the radiating properties, a body will be black when
(Where a = absorptivity, p = reflectivity, X = transmissivity.)

P = 0, x = 0 and a = 1
P= 1, T = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 0

Q.24

The unit of overall coefficient of heat transfer is

kcal/m²
kcal/hr °C
kcal/m² hr °C
kcal/m hr °C

Q.25

Unit of thermal conductivity in S.I. units is

J/m² sec
J/m °K sec
W/m °K
Option (B) and (C) above

Q.26

According to Wien's law, the wavelength corresponding to maximum energy is proportion to

Absolute temperature (T)
I²
F
T

Q.27

Which of the following has least value of conductivity?

Glass
Water
Plastic
Air

Q.28

According to Prevost theory of heat exchange

It is impossible to transfer heat from low temperature source to t high temperature source
Heat transfer by radiation requires no medium
All bodies above absolute zero emit radiation
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

Q.29

When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Conduction
Convection
Radiation
Conduction and convection

Q.30

The concept of overall coefficient of heat transfer is used in case of heat transfer by

Conduction
Convection
Radiation
Conduction and convection

The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

The use of heat exchangers is made in

The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

Which of the following statement is wrong?

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

Planck’s law holds good for

Thermal conductivity of a material may be defined as the

A perfect black body is one which

Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called

The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as

Depending on the radiating properties, a body will be white when (Where a = absorptivity, p = reflectivity, x = transmissivity)

In heat transfer, conductance equals conductivity (kcal/hr/sq.m/°C/cm) divided by

Depending on the radiating properties, body will be transparent when (Where a = absorptivity, p = reflectivity, x = transmissivity)

The expression Q = ρ AT4 is called

The time constant of a thermocouple is

The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit

Heat transfer takes place as per

Thermal diffusivity is

Conduction is a process of heat transfer

According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

Total emissivity of polished silver compared to black body is

Depending on the radiating properties, a body will be black when (Where a = absorptivity, p = reflectivity, X = transmissivity.)

The unit of overall coefficient of heat transfer is

Unit of thermal conductivity in S.I. units is

According to Wien's law, the wavelength corresponding to maximum energy is proportion to

Which of the following has least value of conductivity?

According to Prevost theory of heat exchange

When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

The concept of overall coefficient of heat transfer is used in case of heat transfer by

0 h : 0 m : 1 s

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Depending on the radiating properties, a body will be white when
(Where a = absorptivity, p = reflectivity, x = transmissivity)

Depending on the radiating properties, body will be transparent when
(Where a = absorptivity, p = reflectivity, x = transmissivity)

Depending on the radiating properties, a body will be black when
(Where a = absorptivity, p = reflectivity, X = transmissivity.)