Black body radiation

  • Thread starter Amith2006
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Sir,
A polished metal plate with a rough black spot on it is heated to about 1400 Kelvin and quickly taken into a dark room. It is said that the black spot will appear brighter than the plate. Is it because the black spot is a perfect black body and hence is a better absorber of heat than the plate?
 

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Andrew Mason
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Amith2006 said:
Sir,
A polished metal plate with a rough black spot on it is heated to about 1400 Kelvin and quickly taken into a dark room. It is said that the black spot will appear brighter than the plate. Is it because the black spot is a perfect black body and hence is a better absorber of heat than the plate?
The plate has a lower emissivity than the black spot (ie it is not a perfect absorber of radiation - it reflects radiation whereas the black spot absorbs almost all incident radiation). So in the black-body radiation equation:

[tex]P = \sigma Ae(T^4)[/tex]

the power emitted by the black spot is higher for the black spot (higher e value).

AM
 

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