Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Photons (compton effect, pair production)

  1. Aug 28, 2005 #1


    User Avatar

    How can a photon knock an electron from a shell, entirely out of the atom?
    (i.e PhotoElectric Effect)

    Photons have 0 rest mass, and little relativistic mass?

    For force, F = ma

    For example, let m = negligable (like the photon's mass is) mass so = mn

    If F = (mn)a and mn is small, then no matter how fast the acceleration, in this case c = 3.0*10^8ms-1, Force will still be negligable.

    Yes, it is true that you cannot use classical mechanics and apply it directly to quantum physics, in this case it would be better to use relatavisitic calculations, but most formula's in QM were developed from classical motion formulas. Just take the bohr radius for example, its a contruction centripetal acceleration (classical circular motion), F = ma is even interpolated in it, Couloms Law and other formula's. This gives the bohr radius 0.0529 * 10^ -10m

    I propose that an electron can only absorb or reflect a photon...
    If it absorbs the photon, the electron will go into an exicted state, i.e its energy will be greater, and it will leave the discrete quantised energy level which requires the electrons to be at a certain energy.

    Both wavefunctions for electrons and photons are on the scale of nano meters or 10^-10 m. Is there a correllation between the W0 (work function) proposed by Einstien, - i.e the minimum energy needed to knock an electron out of an atom, and the wavelength of an electron in a particular energy level to the wavelength of the incident photon that has W0?
    Maybe wavefunctions of the same frequency or wavelength determine wheter a photon is absorbed or reflected?

    And why do we talk of photons as is they are comparable in anyway to a fermion or hadron? Like when we say when an electron jumps from a higher shell to a lower shell, it will emit one red photon for example.
  2. jcsd
  3. Aug 28, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    There are so many things that are wrong in here, I don't even know where to start.

    1. You must have slept through the class when Special Relativity was being taught. Photons have MOMENTUM. Now it is up to you to go look up how it can have a momentum but no rest mass.

    2. A photoelectric effect is done on SOLIDS such as metals. The conduction electrons are the ones typically involved in such a process. These electrons are not tired to any atom, but rather to the band structure of the metal. There are no photoionization involved.

    3. A photon isn't "absorbed" by an electron. This is impossible since it violates several conservation rules.

    4. A photon, however, CAN be absorbed by the whole atom, or the solid. The energy level that we all love is the result of WHOLE system, not just the electron (look at the Hamiltonian if you don't believe me). The atom, or solid, absorbs the photon, causing a transition.

    5. The work function has nothing to do with the photon. It has everything to do with the property of the material itself. It doesn't even have anything directly to do with the individual atoms in the material.

    Someone else can tackle the rest.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Photons (compton effect, pair production)
  1. Compton Effect (Replies: 3)

  2. Compton effect (Replies: 3)

  3. Compton effect (Replies: 3)