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Photoelectric effect (questions)

  1. Mar 21, 2008 #1
    hi, Just had a few questions on the topic.

    With say a sheet of metal exposed to sun light, what happens when all the electrons are gone? Is it still a sheet of metal? Just without the negative charge? will it look any different?

    And how long until all electrons are gone? Is there a life time limit for solar panels converting light to energy?

    Thanks in Advance.
  2. jcsd
  3. Mar 21, 2008 #2


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    Staff: Mentor

    Assuming that the metal is isolated, that is, not part of an electric circuit...

    When you knock some (negatively charged) electrons off, the metal becomes positively charged, right? What does that positive charge do when you try to knock more (negatively charged) electrons off?
  4. Mar 21, 2008 #3

    Andy Resnick

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    I'm not sure, but I think you are confusing the photelectric effect and how photovoltaics work. Solar cells don't have free electrons shooting off a surface; electrons are promoted from the valence to conduction band, where they participate in a closed circuit of current. As electrons leave the device, new ones are brought in (becasue the circuit is closed).

    For the photoelectric effect, as electrons are liberated, the work function must increase- it becomes more difficult to liberate additional electrons.
  5. Mar 21, 2008 #4
    thanks for the help.

    So after a while no more electrons will be free on the peice of metal?

    What about high energy gamma rays. Can they strip the atoms of every electron in every electron shell?

    Then would it still look & be a peice of metal?

  6. Mar 21, 2008 #5
    Electrons from the environment would be quickly attracted to the metal and repopulate the atoms that earlier lost them. It is a common thing for materials to lose electrons and then get some back again. All of your experiences with static electricity, like clingy clothes coming out of the drier, or if you rub a balloon on your sweater and them it will stick to the wall, in such cases friction has scraped electrons off of atoms. When the stickiness goes away that means the population of electrons has gone back to normal. It will go back to normal faster for a metal than for other materials. Going back to the neutral condition is slowest for insulators.
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