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How can low energy light be detected if it's too weak to knock out an electron?

  1. Dec 17, 2012 #1
    A long wavelength light has too little energy to knock out electrons, so how do scinetists detect them? and how does a light with low energy ever cease to exist since it can never be absorbed?
     
  2. jcsd
  3. Dec 17, 2012 #2

    DrDu

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    Do you know how a radio works?
     
  4. Dec 17, 2012 #3
    I have taken a look at it, but don't fully get it, something about the magnetic field of the wave pushing current..


    but then I just thought, to push a current is kind of like knocking out electrons, since they are jumping from their atoms.

    oh but to push a current the wave needs to behave like a wave and interact with its magnetic field with the metal atoms, without collapsing, but waves interacting behave as particles? now I'm just more and more confused.
     
  5. Dec 17, 2012 #4

    DrDu

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    The wave accelerates the electrons in a metal due to their electric field, i.e. electric currents are induced. The electrons in a metal are not bound to any specific ions but can move freely. However the accelerated electrons can also scatter from the atomic cores and thus loose the energy they received from the electric field creating thermal motion of the atoms, i.e. heat. That's the reason for the resistance of metals.
    In a radio, basically the currents induced are used to move the membrane of the loud speakers. This also diminishes the current as the energy of the currents is converted into sound waves.
     
  6. Dec 17, 2012 #5
    so the interstellar telescopes are basically just giant radio-antennas who turn the information into pictures.
     
  7. Dec 17, 2012 #6

    Drakkith

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    Staff: Mentor

    Yep.
     
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