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Quesitons about scattering of light

  1. Aug 6, 2015 #1

    kelvin490

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    Gold Member

    I have several questions about the scattering of light.

    Air molecules scatter sunlight and makes the sky blue, many books say that the air molecules are oscillated by E field and so they becomes sources of EM wave. Is it because the air molecules have charges? I wonder if air molecules or molecules of other medium (e.g. water) are completely neutral (i.e. no excess charges at all), will they still be oscillated by the E field and scatter light?

    Air molecules can be oscillated by E field and re-radiate EM waves in different directions. However, if light is shined to a conductor the E field oscillate the free charges but the effect is to reflect the light or dissipated the energy by electrical resistance. Why there is such a difference?
     
    Last edited: Aug 6, 2015
  2. jcsd
  3. Aug 6, 2015 #2
    Yes, most of the air molecules are neutral. However the electric field will act on their electrons (mainly, due to their lower mass) and slightly distort the equilibrium configuration, resulting in a temporary (oscillating) dipole. This oscillating dipole radiates EM waves. This is a simplified model, of course.
    The effect on metals is much stronger because the electrons are "free" and not bound to specific ion cores.
     
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