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Mirrors, Atoms and Light Question

  1. May 10, 2010 #1
    According to my knowledge and understanding of things, mirrors reflect light perfectly because they are almost perfectly flat, or at least uniformly flat at most places.
    (\ and / are light rays)


    But if all matter is composed of atoms, then a mirror would not be flat and would look like this (_ and \ are light rays)
    therefore light would not reflect perfectly, and mirrors would just look like a white surface.
    But this is obviously not the case. Why? What am I misunderstanding?
    Thanks in advance.
  2. jcsd
  3. May 10, 2010 #2


    Staff: Mentor

    My guess is that the imperfections in the glass are much smaller than the wavelength of visible light, which is 390 to 750 nm.
  4. May 11, 2010 #3

    Andy Resnick

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    No, surfaces are good reflectors because they don't transmit or absorb. Specifically 'why' depends on the nature of the reflecting surface- it can be an interference effect (thin film bragg reflectors) or because the material is conductive (metallic reflectors), it can be total internal reflection, or perhaps some other effect.

    'good' mirrors are flat, yes- or rather, smooth on the scale of the wavelength. Atoms are much smaller than a wavelength.
  5. May 11, 2010 #4

    Claude Bile

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    If the phase "error" induced by a rough surface is much smaller than the wavelength, then the surface will still appear smooth. The surface roughness of a typical optical element for example is the wavelength/8.

  6. May 14, 2010 #5


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    On the atomic scale, what causes reflection? how does it work?
  7. May 14, 2010 #6


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    In metals the electrons are not localized but distributed over the whole piece of metal. As the electronic structure is "smoothed" out the light waves are reflected by a nearly homogeneous structure, not by localized structures.
  8. May 14, 2010 #7

    Andy Resnick

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    That's a very open-ended question, and generally leads to a never-ending series of "but what caused that?" type questions.

    Fundamentally, reflection is like any other scattering process, involving the interaction of light and matter.
  9. May 14, 2010 #8
    Maybe get a book on quantum optics or feynmans book - QED: The Strange Theory of Light and Matter
  10. May 14, 2010 #9


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    The way I think of it is, the incident light wave causes electrons near the material surface to oscillate at the same frequency as the light. The oscillating electrons emit waves of the same frequency, and that is seen as outgoing, reflected light ... as well as transmitted (refracted) light if the material is transparent.
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