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In photoelectric effect mass reduce or increase ?

  1. Nov 2, 2012 #1
    Hello all
    when atom absorbed a photon , photon changes to virtual photon in atom and mass of atom must increase .
    but in other form electron absorbed the photon and pull off atom like photoelectric effect .
    My question is in photoelectric effect , mass of metal base increase or decrease and what happen to the photon that metal base absorbed ?
    sorry for my english
  2. jcsd
  3. Nov 2, 2012 #2
    when an atom absorbs photon,it means that photon is destroyed(it is not inside the atom) and when it comes out ,it means a photon has been created.it does not mean any more in quantum theory of radiation.
  4. Nov 2, 2012 #3
    When the photon is absorbed by an atom, the energy of the photon serves to increase the energy of the atom, not its mass. The energy is then transferred to an orbiting electron allowing it to transition to a higher energy level.
  5. Nov 2, 2012 #4

    Simon Bridge

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    The mass of the metal goes down by the mass of the ejected electrons.
    The energy of the photon goes to potential and kinetic energy in the ejected electron.
    Other replies have addressed the other misconceptions.
    I'm guessing you have been thinking of the mass-energy relation here?
  6. Mar 28, 2013 #5
    ANS-The Photoelectric Effect is a phenomenon where electrons can be emitted from the surface of a metal when light of a sufficiently small wavelength shines on the surface. Note that the electrons typically only come off when there is an electric field that *pulls* them off!

    The atoms stay behind (the nucleus and the rest of the electrons); they do not leave the metal, but they do become positively charged (because they are missing an electron). If this happens many times, and many electrons are pulled off the metal, the metal will gain a noticeable positive charge (because the negative charges have left the metal!). This positive charge will quickly begin to attract *other* electrons to come back to the metal, neutralizing the metal. If you somehow try to prevent this, the charge will keep building up until it is very hard to pull more electrons off in the first place. So the mass of the metal will not change over time -- eventually it will pull back the missing electrons and have the same mass as before.
  7. Mar 28, 2013 #6


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    Er... hang on. There are several misleading information being given in here.

    First of all, the typical photoelectric effect is done on metals. This means that the electrons involved are conduction electrons (i.e. they reside in the metal's conduction BANDS, not in some atomic orbitals).

    Secondly, the metals are grounded, so any electrons leaving the metals are quickly replenished to prevent charging effects.

    Thirdly, one does not need to apply any kind of a field to "pull off" the electrons. In photoemission spectroscopy experiments, such fields are, in fact, detrimental to what we want to study, because the field will add extra energies and modify the electron's trajectory, which is not something we want.

    Finally, all the theoretical description of the photoelectric effect includes no "mass increase" of any kind. The energy of the original photon is well-accounted for in overcoming the work function, binding energy inside the solid, and in the kinetic energy of the photoelectrons.

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