Related Questions

Absorptivity of a body will be equal to its emissivity
A At all temperatures
B At one particular temperature
C When system is under thermal equilibrium
D At critical temperature
Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity?
A Aluminium foil
B Refractory bricks
C Iron plate
D Coke breeze
In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)
A α = 1; ε ≠ 1
B α ≠ 1, ε = 1
C α ≠ 1, ε ≠ 1
D α = 1; ε = 1
The sum of reflectivity and absorptivity for an opaque body is equal to
A 0.5
B 1
C 0
D 2
Emissivity of a white polished body in comparison to a black body is
A Higher
B Lower
C Same
D Depends upon the shape of body
The emissivity of a polished silver body is _________ as compared to black body.
A Same
B Low
C Very low
D High
A body is called grey if the monochromatic emissivity of the body is
A Zero
B Unity
C Same for all wavelengths
D Different for all wavelengths
While the total emissivity of a perfect black body is unity, the same for a real body is
A 0
B 1
C > 1
D Between 0 and 1
Heat transfer by radiation from a hot body will be most rapid, if its surface is __________ because of its higher emissivity.
A White & rough
B Black & rough
C White & polished
D Black & polished
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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