Wiens law states that the wave length corresponding to ________ is proportional to the absolute temperature.
Minimum energy
Maximum energy
Both (A) and (B)
None of these
Correct Answer :
B. Maximum energy
Related Questions
Thermal diffusivity is
A dimensionless parameter
Function of temperature
Used as mathematical model
A physical property of the material
In heat exchangers, degree of approach is defined as the difference between temperatures of
Cold water inlet and outlet
Hot medium inlet and outlet
Hot medium outlet and cold water inlet
Hot medium outlet and cold water outlet
Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
h = k/ ρS
h = ρS/k
h = S/ρk
h = kρ/S
The heat transfer takes place according to
Zeroth law of thermodynamics
First law of thermodynamics
Second law of thermodynamics
Kirchhoff's law
In case of liquids and gases, the heat transfer takes place according to
Conduction
Convection
Radiation
None of these
The most commonly used method for the design of duct size is the
Velocity reduction method
Equal friction method
Static regains method
Dual or double method
Thermal diffusivity of a substance is
Directly proportional to thermal conductivity
Inversely proportional to density of substance
Inversely proportional to specific heat
All of the above
Thermal conductivity of non-metallic amorphous solids with decrease in temperature
Increases
Decreases
Remain constant
May increase or decrease depending on temperature
The transfer of heat by molecular collision is smallest in
Solids
Liquids
Gases
None of these
Heat is closely related with
Liquids
Energy
Temperature
Entropy
In heat transfer, conductance equals conductivity (kcal/hr/sq.m/ °C/cm) divided by
Hr (time)
Sq. m (area)
°C (temperature)
K.cal (heat)
Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
1 : 1
2 : 1
1 : 2
4 : 1
The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as
Thermal coefficient
Thermal resistance
Thermal conductivity
None of these
A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
k₁ k₂
(k₁ + k₂)
(k₁ + k₂)/ k₁ k₂
2 k₁ k₂/ (k₁ + k₂)
Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
Thermal resistance
Thermal coefficient
Temperature gradient
Thermal conductivity
Film coefficient is defined as the ratio of
Thermal conductivity to the equivalent thickness of the film of fluid
Temperature drop through the films of fluids to the thickness of film of fluids
Thickness of film of fluid to the thermal conductivity
Thickness of film of fluid to the temperature drop through the films of fluids
Cork is a good insulator because it has
Free electrons
Atoms colliding frequency
Low density
Porous body
If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of
6
9
27
81
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)
Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)
Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]
Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)
Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)
The unit of Stefan Boltzmann constant is
Watt/cm² °K
Watt/cm4 °K
Watt²/cm °K⁴
Watt/cm² °K⁴
The highest thermal diffusivity is of
Iron
Lead
Concrete
Wood
The use of heat exchangers is made in
Radiators in automobile
Condensers and boilers in steam plants
Condensers and evaporators in refrigeration and air conditioning units
All of the above
The heat transfer by conduction through a thick sphere is given by
Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)
Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)
Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)
Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)
A steam pipe is to be insulated by two insulating materials put over each other. For best results
Better insulation should be put over pipe and better one over it
Inferior insulation should be put over pipe and better one over it
Both may be put in any order
Whether to put inferior OIL over pipe or the better one would depend on steam temperature
Reynolds number is the ratio of
Energy transferred by convection to that by conduction
Kinematic viscosity to thermal diffusivity
Inertia force to viscous force
None of the above
The ratio of surface convection resistance to the internal conduction resistance is known as
Grashoff number
Biot number
Stanton number
Prandtl number
The rate of energy transferred by convection to that by conduction is called
Stanton number
Nusselt number
Biot number
Peclet number
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
Absolute temperature
T²
T⁵
T
The expression Q = ρ AT4 is called
Fourier equation
Stefan-Boltzmann equation
Newton Reichmann equation
Joseph-Stefan equation
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
Grey body
Brilliant white polished body
Red hot body
Black body