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4

Heat transfer by radiation mainly depends upon

A. Its temperature

B. Nature of the body

C. Kind and extent of its surface

D. All of the above

Correct Answer :

D. All of the above


Related Questions

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Fourier's law of heat conduction is valid for

A. One dimensional cases only

B. Two dimensional cases only

C. Three dimensional cases only

D. Regular surfaces having non-uniform temperature gradients

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4

In regenerator type heat exchanger, heat transfer takes place by

A. Direct mixing of hot and cold fluids

B. A complete separation between hot and cold fluids

C. Flow of hot and cold fluids alternately over a surface

D. Generation of heat again and again

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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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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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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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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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The thermal diffusivities for solids are generally

A. Less than those for gases

B. Less than those for liquids

C. More than those for liquids and gases

D. More or less same as for liquids and gases

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4

The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

A. Equal to one

B. Greater than one

C. Less than one

D. Equal to Nusselt number

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4

Heat transfer by radiation mainly depends upon

A. Its temperature

B. Nature of the body

C. Kind and extent of its surface

D. All of the above

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4

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 diffusivity is a

A. Function of temperature

B. Physical property of a substance

C. Dimensionless parameter

D. All of these

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Upto the critical radius of insulation,

A. Added insulation will increase heat loss

B. Added insulation will decrease heat loss

C. Convective heat loss will be less than conductive heat loss

D. Heat flux will decrease

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4

Total heat is the heat required to

A. Change vapour into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid or vapour

D. Convert water into steam and superheat it

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4

The heat transfer takes place according to

A. Zeroth law of thermodynamics

B. First law of thermodynamics

C. Second law of thermodynamics

D. Kirchhoff's law

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Unit of thermal conductivity in S.I. units is

A. J/m² sec

B. J/m °K sec

C. W/m °K

D. Option (B) and (C) above

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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

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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 unit of overall coefficient of heat transfer is

A. W/m²K

B. W/m²

C. W/mK

D. W/m

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Which of the following statement is correct?

A. A grey body is one which absorbs all radiations incident on it.

B. At thermal equilibrium, the emissivity and absorptivity are same.

C. The energy absorbed by a body to the total energy falling on it, is called emissivity.

D. A perfect body is one which is black in colour.

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4

According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

A. Directly proportional to the surface area

B. Directly proportional to the difference of temperatures between the two bodies

C. Either (A) or (B)

D. Both (A) and (B)

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Sensible heat is the heat required to

A. Change vapour into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid of vapour

D. Convert water into steam and superheat 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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All radiations in a black body are

A. Reflected

B. Refracted

C. Transmitted

D. Absorbed

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The automobile radiator is a heat exchanger of

A. Parallel flow type

B. Counter flow type

C. Cross flow type

D. Regenerator type

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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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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

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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4

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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4

Temperature of steam at around 540°C can be measured by

A. Thermometer

B. Thermistor

C. Thermocouple

D. None of these

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4

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