Home

What is the correct answer?

4

The highest thermal diffusivity is of

A. Iron

B. Lead

C. Concrete

D. Wood

Correct Answer :

B. Lead


Related Questions

What is the correct answer?

4

The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

A. Move actually

B. Do not move actually

C. Affect the intervening medium

D. Does not affect the intervening medium

What is the correct answer?

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

What is the correct answer?

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

What is the correct answer?

4

The product of Reynolds number and Prandtl number is known as

A. Stanton number

B. Biot number

C. Peclet number

D. Grashoff number

What is the correct answer?

4

According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

A. Grey body

B. Brilliant white polished body

C. Red hot body

D. Black body

What is the correct answer?

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

What is the correct answer?

4

A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

A. h₁ + h₂ + h₃

B. (h₁.h₂.h₃)1/3

C. 1/h₁ + 1/h₂ + 1/h₃

D. None of these

What is the correct answer?

4

The heat of sun reaches to us according to

A. Conduction

B. Convection

C. Radiation

D. None of these

What is the correct answer?

4

Thermal conductivity of glass wool varies from sample to sample because of variation in

A. Composition

B. Density

C. Porosity

D. All of the above

What is the correct answer?

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

What is the correct answer?

4

Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

A. k. A. (dT/dx)

B. k. A. (dx/dT)

C. k. (dT/dx)

D. k. (dx/dT)

What is the correct answer?

4

When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

What is the correct answer?

4

In counter flow heat exchangers

A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

B. Both the fluids at inlet are in their hottest state

C. Both the fluids at exit are in their hottest state

D. One fluid is in hottest state and other in coldest state at inlet

What is the correct answer?

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

What is the correct answer?

4

When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a

A. Black body

B. Grey body

C. Opaque body

D. White body

What is the correct answer?

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

What is the correct answer?

4

The highest thermal diffusivity is of

A. Iron

B. Lead

C. Concrete

D. Wood

What is the correct answer?

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.

What is the correct answer?

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

What is the correct answer?

4

Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

A. One

B. Two

C. Three

D. Four

What is the correct answer?

4

Moisture would find its way into insulation by vapour pressure unless it is prevented by

A. High thickness of insulation

B. High vapour pressure

C. Less thermal conductivity insulator

D. A vapour seal

What is the correct answer?

4

In case of liquids and gases, the heat transfer takes place according to

A. Conduction

B. Convection

C. Radiation

D. None of these

What is the correct answer?

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

What is the correct answer?

4

A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

A. The better insulation must be put inside

B. The better insulation must be put outside

C. One could place either insulation on either side

D. One should take into account the steam temperature before deciding as to which insulation is put where

What is the correct answer?

4

The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)

A. tm = (Δt1 - Δt2)/ loge (Δt1/Δt2)

B. tm = loge (Δt1/Δt2)/ (Δt1 - Δt2)

C. tm = tm = (Δt1 - Δt2) loge (Δt1/Δt2)

D. tm = loge (Δt1 - Δt2)/ Δt1/Δt2

What is the correct answer?

4

Joule sec is the unit of

A. Universal gas constant

B. Kinematic viscosity

C. Thermal conductivity

D. Planck's constant

What is the correct answer?

4

All radiations in a black body are

A. Reflected

B. Refracted

C. Transmitted

D. Absorbed

What is the correct answer?

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

What is the correct answer?

4

Stefan Boltzmann law is applicable for heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Conduction and radiation combined

What is the correct answer?

4

The heat is transferred by conduction, convection and radiation in

A. Melting of ice

B. Boiler furnaces

C. Condensation of steam in condenser

D. None of these