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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

Correct Answer :

D. Time


Related Questions

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4

The value of Prandtl number for air is about

A. 0.1

B. 0.3

C. 0.7

D. 1.7

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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 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

The amount of radiation mainly depends upon the

A. Nature of the body

B. Temperature of the body

C. Type of surface of the body

D. All of these

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4

Stefan Boltzmann law is applicable for heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Conduction and radiation combined

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4

The critical thickness of insulation for a sphere is

A. k/h₀

B. 2k/h₀

C. h₀/k

D. h₀/2k

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4

The unit of Stefan-Boltzmann constant is

A. Watt/mK

B. Watt/m²K²

C. Watt/m²K4

D. Watt/mK²

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4

The time constant of a thermocouple is

A. The time taken to attain the final temperature to be measured

B. The time taken to attain 50% of the value of initial temperature difference

C. The time taken to attain 63.2% of the value of initial temperature difference

D. Determined by the time taken to reach 100°C from 0°C

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4

LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is

A. Higher

B. Lower

C. Same

D. Depends on the area of heat exchanger

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4

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

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

A. Absolute temperature (T)

B.

C. F

D. T

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4

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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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

In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.

A. Same

B. Less

C. Greater

D. None of these

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4

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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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

Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in

A. Electric heater

B. Steam condenser

C. Boiler

D. Refrigerator condenser coils

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4

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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4

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

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

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4

Kirchhoff's law states that

A. The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature

B. The wave length corresponding to the maximum energy is proportional to the absolute temperature

C. 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

D. None of the above

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4

The rate of energy transferred by convection to that by conduction is called

A. Stanton number

B. Nusselt number

C. Biot number

D. Peclet number

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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. Kirchoffs law

B. Stefan's law

C. Wien' law

D. Planck's law

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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

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

Pick up the wrong case. Heat flowing from one side to other depends directly on

A. Face area

B. Time

C. Thickness

D. Temperature difference

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4

According to Prevost theory of heat exchange

A. It is impossible to transfer heat from low temperature source to t high temperature source

B. Heat transfer by radiation requires no medium

C. All bodies above absolute zero emit radiation

D. Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

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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

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

A. Absolute temperature

B.

C. T⁵

D. T

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4

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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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