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The mass of photon

  1. May 17, 2007 #1
    "the mass of photon"

    I definitely know that photons don't have any mass if it is moving with it's well-known speed. However, it has its rest mass. So my question is

    The energy of photons depend on their frequencies, however the freq. may differ from photon to photon. So I think their rest mass should also differ from photon to photon...

    Am I right, or .....?
    thanks a lot
  2. jcsd
  3. May 17, 2007 #2

    Doc Al

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    Staff: Mentor

    Photons are massless--they have zero rest mass.
  4. May 17, 2007 #3
    And that speed is always a constant (i.e. has the same value irrespective of the frame of reference) having the value c. The rest mass of any particle which moves with speed = c will have zero rest mass.
    You're not quite right in the sense that you're speaking about two different definitions of mass as if they were one. The value E = pc for a photon means that its rest mass is zero but that its inertial mass is not zero.

  5. May 18, 2007 #4
    I asked this same question many moons ago
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