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B What actually is threshold frequency?

  1. Oct 9, 2016 #1
    For example a metal atom have 3 electrons which occupies 2 energy level. Is the threshold frequency = the energy needed to bring an electron in E2 to E(infinity) / h?
  2. jcsd
  3. Oct 9, 2016 #2


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    You need to understand one very important concept here. When atoms are together to form a solid, many of the individual properties of isolated atoms are no longer relevant. A solid has many properties that an individual atom does not have. This includes the formation of "energy bands" in solids, whereas in atoms, you have discrete energy levels.

    So your question here doesn't make any sense because you are asking a question about a "metal", which is a solid, based on the valence shell of an individual atom. While this may be relevant when one probes deeper energy state of the metal, it is no longer relevant when you talk about "threshold" frequency or energy to cause the first ionization.

    For example, the first ionization energy of Cu atom is ~7.7 eV. Yet, for Cu metal, the work function, and thus, the threshold energy for photoemission, is ~4.6 eV. These two numbers are different!

    More is Different! Solid state physics is not simply "a lot of atomic physics".

  4. Oct 9, 2016 #3
    Thanks for telling me that an atom from a metal has different properties from a metal.

    So work function is a term for a solid only?

    If I consider an atom only, is "threshold frequency * h" or "energy to cause the first ionization "= The energy needed to raise an electron from the highest energy level to infinity?

    thanks a lot
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