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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

Correct Answer :

D. Different temperatures


Related Questions

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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

An ordinary passenger aircraft requires a cooling system of capacity.

A. 2 TR

B. 4 TR

C. 8 TR

D. 10 TR

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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

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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4

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.

A. Equal to

B. Directly proportional to

C. Inversely proportional to

D. None of these

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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

The amount of heat flow through a body by conduction is

A. Directly proportional to the surface area of the body

B. Directly proportional to the temperature difference on the two faces of the body

C. Dependent upon the material of the body

D. All of the above

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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 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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4

The emissivity for a black body is

A. 0

B. 0.5

C. 0.75

D. 1

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4

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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4

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

A. First law of thermodynamics

B. Newton's law of cooling

C. Newton's law of heating

D. Stefan's law

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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 heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

A. Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)

B. Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]

C. Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)

D. Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)

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4

Log mean temperature difference in case of counter flow compared to parallel flow will be

A. Same

B. More

C. Less

D. Depends on other factors

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4

Which of the following has maximum value of thermal conductivity?

A. Aluminium

B. Steel

C. Brass

D. Copper

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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

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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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

Fouling factor is used

A. In heat exchanger design as a safety factor

B. In case of Newtonian fluids

C. When a liquid exchanges heat with a gas

D. None of the above

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4

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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4

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 unit of Stefan Boltzmann constant is

A. Watt/cm² °K

B. Watt/cm4 °K

C. Watt²/cm °K⁴

D. Watt/cm² °K⁴

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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

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

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

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

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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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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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