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When are materials heated

  1. Mar 17, 2012 #1
    no its not a homework question it was in a quiz but i believe the teacher is wrong about it
    materials are heated when they absorb:
    -electromagnetic radiation of any type
    -infrared radiation only
    -microwaves and infrared only

    please choose and explain
    Thanks in advance
     
  2. jcsd
  3. Mar 17, 2012 #2

    DaveC426913

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    What was your answer? Explain.
     
  4. Mar 17, 2012 #3
    my answer was a)electromagnetic radiation of any type
    I am in grade 10 IGCSE I don't have a lot of background in physics but I thought that visible light(which is part of the electromagnetic spectrum)is able to heat objects
    like in lamps
    and in nuclear fission when gamma radiation is emitted from the U-236 nuclei it heats the water to produce steam that runs the generator
     
  5. Mar 17, 2012 #4

    DaveC426913

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    That would be my answer too.

    It is true that some materials are transparent to certain frequencies of radiation. But if that were true, then one would not say that the material absorbed that frequency.

    So if it's absorbed at all, it will result in a rise in temperature.
     
  6. Mar 17, 2012 #5
    Thanks for your quick reply
     
    Last edited: Mar 17, 2012
  7. Mar 17, 2012 #6

    DaveC426913

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    Your teacher may be thinking of examples like how a glass window is not heated by visible light. Well, that's because the light passes through the window; it is not absorbed.

    And the question as you wrote it specifically says "absorbed".
     
  8. Mar 17, 2012 #7
    I believe that will simplify many things,the question really did say "absorbed"
    Man thanks a lot
    and sorry for my poor english
     
  9. Mar 17, 2012 #8
    A superconducting antena could absorb a radio signal without heating up. The energy would be passed along to the reciever without loss so energy in = energy out.

    This opens up a debate about what constitutes "absorption". Does an antena absorb the radio wave and produce an electrical output or does it focus energy on the reciever like a lense or mirror?
     
  10. Mar 17, 2012 #9

    sophiecentaur

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    The antenna itself would not absorb energy - the load to which it was connected would, however. If there were no resistive element involved, the EM would just be reflected / scattered. The whole receiving apparatus would not (could not - by definition) be a superconductor.
     
  11. Mar 17, 2012 #10
    guys Im lost
    what does that mean?
     
  12. Mar 17, 2012 #11
    They were hypothesizing about some perfectly efficient way of converting radio waves into electrical energy without losing energy to heat. But, for all practical purposes, we always get some heat when we convert energy from one form to another.
     
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