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Why does electromagnetic radiation (energy) excite electrons?

  1. Oct 21, 2012 #1
    Hello everyone,

    I've been told many times that when the right frequency of electromagnetic radiation hits an electron, it is excited to another energy level. My question is this, "why do electrons get excited to higher energy levels when hit by electromagnetic radiation?" Why does the cause (being hit by electromagnetic radiation) bring about the effect (raising the electron to a higher energy level)? If you could answer this for me, it would be great.

    Thanks,

    Vanmaiden
     
  2. jcsd
  3. Oct 21, 2012 #2
    Because the electrons are charged particles, and they interact with the electromagnetic field. As for the condition for the right frequency, it follows from the law of conservation of energy during the process.
     
  4. Oct 21, 2012 #3
    Electromagnetic waves contain electric fields, and electric fields push on charges. So that's why being hit by electromagnetic waves affects electrons: the electric field pushes the charge around.

    Now, why does the effect depend on the frequency of the wave? Imagine you are pushing someone in a swing, trying to get them swinging higher. You'll need to repeatedly push them at a certain frequency, so that you always push them while they're swinging forward (speeding them up) instead of pushing them while they are swinging backwards (slowing them down). An analogous thing happens in atoms: in order to get the electron vibrating in a certain way, you need to push on it with electric fields at a certain frequency, so you need to hit it with an electromagnetic wave of a certain frequency.
     
  5. Oct 21, 2012 #4

    Drakkith

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    Staff: Mentor

    The EM wave exerts a force on the electron. In a conductor such as an antenna there are practically an unlimited amount of energy states available for many of the electrons so all frequencies will excite electrons, causing them to move. In a non-conductor only certain energy states are available, so some of the light is going to be the wrong frequency and will either be reflected or passed through instead of absorbed.
     
  6. Oct 21, 2012 #5
    When an electromagnetic wave pushes on the electron, what causes the electron to release energy in the form of radiation?
     
  7. Oct 21, 2012 #6

    Drakkith

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    Staff: Mentor

    It doesn't. The opposite happens and it absorbs energy.
     
  8. Oct 22, 2012 #7
    For a different but related perspective, try reading a the first section or two here:

    http://en.wikipedia.org/wiki/Energy_level

     
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