If an object can absorb its thermal radiation falling on it without any reflection or dispersion, then it is called black object or black body. It can radiates its own heat and temperature completely. The emissivity of an ideal black body is most, assumed as one in the same environment; a black body absorbs, and excludes temperature faster than a body, which is not black.
What is black body characteristics?
The ultra-reagent heat absorber surfaces have the following characteristics-
- The color is, as much closer as black, it will absorb as much as radiation.
- Whatever the color of the surface’s smoothness, small or rough surface can absorb much radiation than the smooth and bright surface. Closed furnaces behave like a black body, which is why an appropriate temperature can be got from it. If the furnace’s radiation can be measured with a small aperture, then the temperature inside the furnace will be measured. Radiation pyrometer is used to measure such kind of temperature.
If, E=the falling radiation on an object (W/m2)
a=partial radiation absorbed by the object
So that, e=aE/E
The emissivity of a common copper foiling rough surface is 0.97 and in a smooth surface is 0.08, cast iron in the rough surface is 0.95 and in the
smoothsurface is 0.21, and aluminum oxide surface is 0.11 in a smooth surface is 0.028. However, the value of emissivity is increased with temperature.