All radiations in a black body are
Reflected
Refracted
Transmitted
Absorbed
Correct Answer :
D. Absorbed
Related Questions
Fourier's law of heat conduction gives the heat flow for
Irregular surfaces
Nonuniform temperature surfaces
One dimensional cases only
Two dimensional cases only
The natural convection air cooled condensers are used in
Domestic refrigerators
Water coolers
Room air conditioners
All of these
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
Conduction
Convection
Radiation
Conduction and convection
Absorptivity of a body will be equal to its emissivity
At all temperatures
At one particular temperature
When system is under thermal equilibrium
At critical temperature
Emissivity of a white polished body in comparison to a black body is
Higher
Lower
Same
Depends upon the shape of body
Which of the following has least value of conductivity?
Glass
Water
Plastic
Air
Depending on the radiating properties, a body will be opaque when
P = 0, x = 0 and a = 1
P=1, x = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.
Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)
RN = hl/k
RN = μ cp/k
RN = ρ V l /μ
RN = V²/t.cp
In counter flow heat exchangers
Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
Both the fluids at inlet are in their hottest state
Both the fluids at exit are in their hottest state
One fluid is in hottest state and other in coldest state at inlet
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
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
Unit of thermal conductivity in M.K.S. units is
K cal/kg m² °C
K cal m/hr m² °C
K cal/hr m² °C
K calm/hr °C
Joule sec is the unit of
Universal gas constant
Kinematic viscosity
Thermal conductivity
Planck's constant
Conduction is a process of heat transfer
From one particle of the body to another without the actual motion of the particles
From one particle of the body to another by the actual motion of the heated particles
From a hot body to a cold body, in a straight line, without affecting the intervening medium
None of the above
An ordinary passenger aircraft requires a cooling system of capacity.
2 TR
4 TR
8 TR
10 TR
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)
The emissivity for a black body is
0
0.5
0.75
1
The ratio of the energy absorbed by the body to total energy falling on it is called
Absorptive power
Emissive power
Absorptivity
Emissivity
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
First law of thermodynamics
Newton's law of cooling
Newton's law of heating
Stefan's law
According to Prevost theory of heat exchange
It is impossible to transfer heat from low temperature source to t high temperature source
Heat transfer by radiation requires no medium
All bodies above absolute zero emit radiation
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
Depending on the radiating properties, a body will be black when
P = 0, x = 0 and a = 1
P= 1, T = 0 and a = 0
P = 0, x = 1 and a = 0
X = 0, a + p = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.
Heat transfer takes place as per
Zeroth law of thermodynamics
First law of thermodynamic
Second law of the thermodynamics
Kirchoff's law
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
The better insulation must be put inside
The better insulation must be put outside
One could place either insulation on either side
One should take into account the steam temperature before deciding as to which insulation is put where
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 perfect black body is one which
Is black in colour
Reflects all heat
Transmits all heat radiations
Absorbs heat radiations of all wave lengths falling on it
The value of the wave length for maximum emissive power is given by
Kirchhoff's law
Stefan's law
Wines law
Planck's law
The concept of overall coefficient of heat transfer is used in heat transfer problems of
Conduction
Convection
Radiation
Conduction and convection
Stefan Boltzmann law is applicable for heat transfer by
Conduction
Convection
Radiation
Conduction and radiation combined
The unit of Stefan-Boltzmann constant is
Watt/mK
Watt/m²K²
Watt/m²K4
Watt/mK²
The heat transfer takes place according to
Zeroth law of thermodynamics
First law of thermodynamics
Second law of thermodynamics
Kirchhoff's law