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4

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

Correct Answer :

D. All of the above


Related Questions

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4

The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

A. Stanton number

B. Biot number

C. Peclet number

D. Grashoff number

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4

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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4

Conduction is a process of heat transfer

A. From one particle of the body to another without the actual motion of the particles

B. From one particle of the body to another by the actual motion of the heated particles

C. From a hot body to a cold body, in a straight line, without affecting the intervening medium

D. None of the above

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4

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

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Heat conducted through per 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

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4

The insulation ability of an insulator with the presence of moisture would

A. Increase

B. Decrease

C. Remain unaffected

D. May increase/decrease depending on temperature and thickness of insulation

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4

Thermal diffusivity is a

A. Function of temperature

B. Physical property of a substance

C. Dimensionless parameter

D. All of these

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4

Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)

A. h = k/ ρS

B. h = ρS/k

C. h = S/ρk

D. h = kρ/S

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4

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

A. Wien's law

B. Stefan's law

C. Kirchhoff's law

D. Planck's law

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4

The critical temperature is the temperature

A. Below which a gas does not obey gas laws

B. Above which a gas may explode

C. Below which a gas is always liquefied

D. Above which a gas will never liquefied

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4

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

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4

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

A. Hr (time)

B. Sq. m (area)

C. °C (temperature)

D. K.cal (heat)

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4

Thermal conductivity of water in general with rise in temperature

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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4

The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as

A. Emissivity

B. Transmissivity

C. Reflectivity

D. Intensity of radiation

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4

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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4

Emissivity of a white polished body in comparison to a black body is

A. Higher

B. Lower

C. Same

D. Depends upon the shape of body

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4

Which of the following has least value of conductivity?

A. Glass

B. Water

C. Plastic

D. Air

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If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of

A. 6

B. 9

C. 27

D. 81

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4

Heat transfer in liquid and gases takes place by

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

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4

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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4

Thermal conductivity of solid metals with rise in temperature normally

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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4

Which of the following is a case of steady state heat transfer?

A. I.C. engine

B. Air preheaters

C. Heating of building in winter

D. None of the above

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4

Thermal diffusivity of a substance is

A. Directly proportional to the thermal conductivity

B. Inversely proportional to density of substance

C. Inversely proportional to specific heat

D. All of the above

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4

The most commonly used method for the design of duct size is the

A. Velocity reduction method

B. Equal friction method

C. Static regains method

D. Dual or double method

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4

Reynolds number is the ratio of

A. Energy transferred by convection to that by conduction

B. Kinematic viscosity to thermal diffusivity

C. Inertia force to viscous force

D. None of the above

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4

Heat flows from one body to other when they have

A. Different heat contents

B. Different specific heat

C. Different atomic structure

D. Different temperatures

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Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

A. RN = hl/k

B. RN = μ cp/k

C. RN = ρ V l /μ

D. RN = V²/t.cp

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4

Heat transfer takes place as per

A. Zeroth law of thermodynamics

B. First law of thermodynamic

C. Second law of the thermodynamics

D. Kirchoff's law

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4

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as

A. Conduction

B. Free convection

C. Forced convection

D. Radiation

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4

The product of Reynolds number and Prandtl number is known as

A. Stanton number

B. Biot number

C. Peclet number

D. Grashoff number