A. At a particular temperature
B. For circular bodies
C. Under thermal equilibrium
D. None of these
Related Mcqs:
- 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 - The sum of reflectivity and absorptivity for an opaque body is equal to____________________?
A. 0.5
B. 1
C. 0
D. 2 - 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 - 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 - Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be_________________?
A. 0.35
B. 0.45
C. 0.55
D. 0.85 - The absorptivity of a grey body at a given temperature _____________ with increasing wavelength of radiation?
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease; depends on the material - Absorptivity and reflectivity of a perfect black body are respectively _______________?
A. 1 and 0
B. 0 and 1
C. 1 and ∞
D. 0 and 0.5 - What is the absorptivity of a black body?
A. 1
B. 0
C. 0.78
D. 0.95 - The ratio of total radiating power to the absorptivity of the body depends upon the _____________ as per Kirchoff‟s law?
A. Wavelength of radiation
B. Nature of the body
C. Temperature of the body
D. None of these - As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the_______________?
A. Temperature of the body only
B. Wavelength of monochromatic radiation
C. Both A. and B.
D. Nature of material of body
