White objects reflect and black objects absorb energy, an ideal black body is defined as one which absorbs all the radiation which falls upon it. However, no perfect blackbody is known. Such a thing would not be seen anyway, being similar to blackhole that can even suck light. A good approximation at the most is a surface painted with lampblack coating. A small hole in the wall of a metal tube appears darker than the surrounding surface, because almost all the light entering the hole is absorbed which is in principle, can be considered a blackbody. Objects whose surfaces are in such condition that they are good absorbers of radiation are also good radiators. If two metal balls, one painted black, are heated in a small furnace, the blackened ball will absorb more energy. Thus, heating, the blackened ball will also radiate more energy.
An ideal blackbody is also an ideal radiator. The implications of a controlled blackbody is efficiently storing energy from a renewable source such as heat from a volcano or radiation from the sun and effectively converting this energy to electrical for consumption. Another illustration of the effect of radiant energy on a body is the radiometer. This device has four vanes mounted at right angles to each other, one side of each vane being white and the other side being black; all of the white sides face the same direction. The vanes are mounted on a low-friction vertical axle and placed in a glass bulb which has been partially evacuated of air. When exposed to radiation, i.e., heat energy, the vanes begin to turn in a motion where the black vanes turning away from heat source. This motion is explained by the fact that the remaining air near the black vane got agitated and thus moves away from the black vane. This movement creates reaction forces that cause the vane to spin if the force is multiplied.
Posted 2011-01-29 and updated on Jun 07, 2011 9:44pm by crisd