A. Zero
B. Unity
C. Same for all wavelengths
D. Different for all wavelengths
Related Mcqs:
- The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body)?
A. αT
B. α × 1/T
C. α T4
D. Independent of T - 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 - 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 - Which one gives the monochromatic emissive power for black body radiation ?
A. Planck’s law
B. Kirchhoff’s law
C. Wien’s law
D. Stefan-Boltzmann law - The absorptivity of a body is equal to its emissivity _________________?
A. At a particular temperature
B. For circular bodies
C. Under thermal equilibrium
D. None of these - What is the emissivity of a black body ?
A. 0
B. 1
C. 0.5
D. 0.90 - 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 - With increase in temperature, the total emissivity of conductors____________________?
A. Increases
B. Decreases
C. Remain same
D. Decreases linearly - The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by__________________?
A. Painting the surface black
B. Painting the surface white (with aluminium paint)
C. Giving the surface a mirror finish
D. Roughening the surface - A _____________ surface has the maximum thermal emissivity out of the following ?
A. Black & smooth
B. Black & rough
C. White & smooth
D. White & rough
