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Photon kinetic energy

  1. Apr 29, 2008 #1
    How is a photon's energy determine in relation to it's wavelength and frequency?
    For example, 20hz vs. 400ghz electromagnetic waves.
  2. jcsd
  3. Apr 29, 2008 #2
    The energy of a photon, E (which can be considered as all kinetic energy since the proper energy = E0 = 0 and E = K + E0 = K), is related to the photon's frequency, f, by E = hf where h = Planck's constant = 6.626068 × 10-34m2kg/s.

  4. Apr 29, 2008 #3
    can E=1/2mv^2 be applied to photons ever?
    or E=mc^2
  5. Apr 29, 2008 #4
    The proper relativistic equation is
    :[tex]E^2 = p^2c^2 + m^2 c^4[/tex], which works just fine for photons when [tex]m = 0[/tex].

    For ordinary particles, one can Taylor expand [tex]E = \sqrt{p^2c^2 + m^2 c^4}[/tex] to get a non-relativistic equation most people use... but for photons, you can't do this, and [tex]E = pc[/tex] simply.

    According to de Broglie, [tex]p = h \nu[/tex], of course.
  6. Apr 30, 2008 #5

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