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4

The emissive power of a body depends upon its

A. Temperature

B. Wave length

C. Physical nature

D. All of the above

Correct Answer :

D. All of the above


Related Questions

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4

Unit of thermal diffusivity is

A. m²/hr

B. m²/hr °C

C. kcal/m² hr

D. kcal/m. hr °C

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4

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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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 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

Free convection flow depends on

A. Density

B. Coefficient of viscosity

C. Gravitational force

D. All of these

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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 transfer of heat by molecular collision is smallest in

A. Solids

B. Liquids

C. Gases

D. None of these

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4

A steam pipe is to be insulated by two insulating materials put over each other. For best results

A. Better insulation should be put over pipe and better one over it

B. Inferior insulation should be put over pipe and better one over it

C. Both may be put in any order

D. Whether to put inferior OIL over pipe or the better one would depend on steam temperature

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4

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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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

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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4

Thermal conductivity of a material may be defined as the

A. Quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C

B. Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

C. Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

D. All of the above

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4

The value of the wavelength for maximum emissive power is given by

A. Wien's law

B. Planck's law

C. Stefan's law

D. Fourier's law

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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

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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4

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

A. α = 1, ρ = 0 and τ = 0

B. α = 0, ρ = 1 and τ = 0

C. α = 0, ρ = 0 and τ = 1

D. α + ρ = 1 and τ = 0

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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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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

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

The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called

A. Conduction

B. Convection

C. Radiation

D. None of these

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4

According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

A. Pb = pa - pv

B. Pb = pa + pv

C. Pb = pa × pv

D. Pb = pa/pv

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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

Depending on the radiating properties, a body will be opaque when

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

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

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

D. X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.

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4

Unit of thermal conductivity in M.K.S. units is

A. K cal/kg m² °C

B. K cal m/hr m² °C

C. K cal/hr m² °C

D. K calm/hr °C

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4

The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as

A. Thermal coefficient

B. Thermal resistance

C. Thermal conductivity

D. None of these

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4

If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called

A. Absorptive power

B. Emissive power

C. Emissivity

D. None of these

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4

The ratio of surface convection resistance to the internal conduction resistance is known as

A. Grashoff number

B. Biot number

C. Stanton number

D. Prandtl number

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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

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 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