A perfect black body is one which

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A perfect black body is one which

A. Is black in colour

B. Reflects all heat

C. Transmits all heat radiations

D. Absorbs heat radiations of all wave lengths falling on it

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Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.

A. Cold body to hot body

B. Hot body to cold body

C. Smaller body to larger body

D. Larger body to smaller body

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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.

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Thermal conductivity of non-metallic amorphous solids with decrease in temperature

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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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

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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

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The unit of overall coefficient of heat transfer is

A. W/m²K

B. W/m²

C. W/mK

D. W/m

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Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

A. One

B. Two

C. Three

D. Four

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Thermal conductivity of wood depends on

A. Moisture

B. Density

C. Temperature

D. All of the above

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Thermal diffusivity of a substance is

A. Directly proportional to thermal conductivity

B. Inversely proportional to density of substance

C. Inversely proportional to specific heat

D. All of the above

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An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

A. 25 mm

B. 40 mm

C. 160 mm

D. 800 mm

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Depending on the radiating properties, body will be transparent when

A. P = 0, x = 0 and a = 1

B. P=1, x = 0, and a = 0

C. P = 0, T= 1, and a = 0

D. X = 0, a + p = 1

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The logarithmic mean temperature difference (t_m) is given by (where Δt₁ and Δt₂ are temperature differences between the hot and cold fluids at entrance and exit)

A. t_m = (Δt₁ - Δt₂)/ log_e (Δt₁/Δt₂)

B. t_m = log_e (Δt₁/Δt₂)/ (Δt₁ - Δt₂)

C. t_m = t_m = (Δt₁ - Δt₂) log_e (Δt₁/Δt₂)

D. t_m = log_e (Δt₁ - Δt₂)/ Δt₁/Δt₂

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The heat transfer by conduction through a thick sphere is given by

A. Q = 2πkr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)

B. Q = 4πkr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)

C. Q = 6πkr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)

D. Q = 8πkr₁ r₂ (T₁ - T₂)/ (r₂ - r₁)

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In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

A. Reynold's number

B. Grashoff's number

C. Reynold's number, Grashoff's number

D. Prandtl number, Grashoff's number

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When heat is transferred by molecular collision, it is referred to as heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Scattering

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Thermal conductivity of water at 20°C is of the order of

A. 0.1

B. 0.23

C. 0.42

D. 0.51

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The transfer of heat by molecular collision is smallest in

A. Solids

B. Liquids

C. Gases

D. None of these

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Which of the following is expected to have highest thermal conductivity?

A. Steam

B. Solid ice

C. Melting ice

D. Water

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According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

A. Absolute temperature

B. Square of the absolute temperature

C. Cube of the absolute temperature

D. Fourth power of the absolute temperature

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Heat transfer in liquid and gases takes place by

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

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Cork is a good insulator because it has

A. Free electrons

B. Atoms colliding frequency

C. Low density

D. Porous body

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40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is

A. 0.45

B. 0.55

C. 0.40

D. 0.75

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The highest thermal diffusivity is of

A. Iron

B. Lead

C. Concrete

D. Wood

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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

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Which of the following is the case of heat transfer by radiation?

A. Blast furnace

B. Heating of building

C. Cooling of parts in furnace

D. Heat received by a person from fireplace

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All radiations in a black body are

A. Reflected

B. Refracted

C. Transmitted

D. Absorbed

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A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

A. h₁ + h₂ + h₃

B. (h₁.h₂.h₃)1/3

C. 1/h₁ + 1/h₂ + 1/h₃

D. None of these

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Film coefficient is defined as Inside diameter of tube

A. Equivalent thickness of film

B. Thermal conductivity Equivalent thickness of film Specific heat × Viscosity

C. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity

D. Film coefficient × Inside diameter Thermal conductivity

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The transfer of heat by molecular collision is known as

A. Conduction

B. Convection

C. Radiation

D. None of these

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Thermal diffusivity is

A. A dimensionless parameter

B. Function of temperature

C. Used as mathematical model

D. A physical property of the material

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Accepted Answer

D. Absorbs heat radiations of all wave lengths falling on it

A perfect black body is one which

Correct Answer :

Show all Heat & Mass Transfer MCQ

Related Questions

Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.

According of Kirchhoff's law

Thermal conductivity of non-metallic amorphous solids with decrease in temperature

A grey body is one whose absorptivity

According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

The unit of overall coefficient of heat transfer is

Thermal conductivity of wood depends on

Thermal diffusivity of a substance is

An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

Depending on the radiating properties, body will be transparent when

The logarithmic mean temperature difference (t_m) is given by (where Δt₁ and Δt₂ are temperature differences between the hot and cold fluids at entrance and exit)

The heat transfer by conduction through a thick sphere is given by

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

When heat is transferred by molecular collision, it is referred to as heat transfer by

Thermal conductivity of water at 20°C is of the order of

The transfer of heat by molecular collision is smallest in

Which of the following is expected to have highest thermal conductivity?

According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Heat transfer in liquid and gases takes place by

Cork is a good insulator because it has

40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is

The highest thermal diffusivity is of

The thermal diffusivities for gases are generally

Which of the following is the case of heat transfer by radiation?

All radiations in a black body are

A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

Film coefficient is defined as Inside diameter of tube

The transfer of heat by molecular collision is known as

Thermal diffusivity is

Also checkout

A perfect black body is one which

Correct Answer :

Show all Heat & Mass Transfer MCQ

Related Questions

Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.

According of Kirchhoff's law

Thermal conductivity of non-metallic amorphous solids with decrease in temperature

A grey body is one whose absorptivity

According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

The unit of overall coefficient of heat transfer is

Thermal conductivity of wood depends on

Thermal diffusivity of a substance is

An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

Depending on the radiating properties, body will be transparent when

The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)

The heat transfer by conduction through a thick sphere is given by

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

When heat is transferred by molecular collision, it is referred to as heat transfer by

Thermal conductivity of water at 20°C is of the order of

The transfer of heat by molecular collision is smallest in

Which of the following is expected to have highest thermal conductivity?

According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Heat transfer in liquid and gases takes place by

Cork is a good insulator because it has

40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is

The highest thermal diffusivity is of

The thermal diffusivities for gases are generally

Which of the following is the case of heat transfer by radiation?

All radiations in a black body are

A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

Film coefficient is defined as Inside diameter of tube

The transfer of heat by molecular collision is known as

Thermal diffusivity is

Also checkout

The logarithmic mean temperature difference (t_m) is given by (where Δt₁ and Δt₂ are temperature differences between the hot and cold fluids at entrance and exit)