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B Transparency and Reflection

  1. Apr 3, 2016 #1
    I'm not sure if this belongs here however some of you may know the answer to my question.
    If I am correct, transparency occurs when light hits an object however the light does not reach the threshold frequency to energize an electron. Thus, the light does not get absorbed and is able to pass through.
    My question is pertaining to reflection. When does reflection happen?
     
  2. jcsd
  3. Apr 3, 2016 #2

    blue_leaf77

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    Resonance frequency.
    Reflection as a result of a phase-matched backward propagation of the waves reemitted by the atoms/molecules/lattices of the object the incoming light is reflected off.
     
  4. Apr 3, 2016 #3
    "Reflection as a result of a phase-matched backward propagation of the waves reemitted by the atoms/molecules/lattices of the object the incoming light is reflected off."
    Thanks for the answer, however I'm not sure if it completely answers what causes the light to reflect.
     
  5. Apr 3, 2016 #4

    blue_leaf77

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    Both reflection and refraction are caused by the medium reemitting light with the same frequency as the incident one. These secondary waves must be emitted such that the wave emitted at different locations in the medium superpose constructively, this is what is called the phase-matched condition. But the primary cause is that the medium reemit the incoming light - photon energy is converted to another photon energy. If most portion of the light is absorbed due to resonance frequency, only little will be reflected and refracted.
     
  6. Apr 4, 2016 #5

    DrDu

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    While that's true, I want to add that many highly absorptive materials reflect light strongly where the absorption coefficient is highest. Try to write with a coloured transparency marker on a black sheet of paper to see what I mean.
     
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