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A Relation between IR radiation and warming in metals

  1. Jun 7, 2016 #1
    As far as I know, in most of metals, IR radiation is reflected almost entirely and is not absorbed by metals. How does a metal become warmed under IR radiation? or does reflection, on its own, can warm up a metal?
     
  2. jcsd
  3. Jun 7, 2016 #2

    Charles Link

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    If you are referring to how sunlight can heat up something like a (hot) metal slide on a playground, it must be that some regions of the solar spectrum must be absorbing the sunlight (perhaps the visible and UV). Another factor that could also play a role in making the metal warm is that if the emissivity is low throughout much of the IR for the metal (for each wavelength, emissivity=1-reflectivity i.e. ## \epsilon(\lambda)=1-R(\lambda) ## . If ## R(\lambda) ## is nearly unity, then emissivity is small.) you won't get much radiative cooling. (You will get conductive cooling from the air). And the other factor that can make the metal feel so warm is the high degree of thermal conduction, so that if you make contact with the metal with a cooler object, heat will flow quickly and steadily into the cooler object. Perhaps this is helpful in answering your question.
     
  4. Jun 8, 2016 #3
    Do you mean that IR, on its own, doesn't warm up a metal?
     
  5. Jun 8, 2016 #4

    Charles Link

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    You would need to look up the spectral characteristics, and impurities and roughened surfaces could affect the reflectivity, but if the reflectivity is in the 95% range or higher, most of the heating is probably coming from other regions of the spectrum. With a very bright source with a lot of IR (such as the sun), even 5% absorption could cause appreciable heating.
     
    Last edited: Jun 8, 2016
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