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Homework Help: Black body radiation

  1. May 24, 2006 #1
    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?
     
  2. jcsd
  3. May 24, 2006 #2

    Andrew Mason

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    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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