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Homework Help: Which photon has more mass?

  1. Jan 19, 2010 #1
    Which of the following has the greatest mass?
    An infra-red photon
    A UV photon
    An optical photon
    An x-ray photon

    This question is on a past exam paper that I'm going through. I thought photons have no rest rest mass, so how can one have more mass than another? I have tried the textbook, the lecture notes and the internet but cant find anything of any use.
  2. jcsd
  3. Jan 19, 2010 #2


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    Gold Member

    Trick question?
  4. Jan 19, 2010 #3
    I thought that, but it seems a bit harsh to put it on a proper exam, when it gives you no option but to answer one ; it's the multiple choice part of the exam.
  5. Jan 19, 2010 #4

    Doc Al

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    Staff: Mentor

    They are most likely talking about the so-called 'relativistic mass', not the usual rest mass. They should have just asked which photon has the greatest energy.

    Read: http://www2.corepower.com:8080/~relfaq/photon_mass.html" [Broken]
    Last edited by a moderator: May 4, 2017
  6. Jan 19, 2010 #5


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    Gold Member

    Ah. Then that would be a nasty trick...
  7. Jan 19, 2010 #6
    ah thanks very much, I didn't think of that.
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