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Absorption of light in a mirror

  1. Oct 10, 2014 #1
    I read in some place that the mirror be it 100 per cent reflective, will also absorb if a light strikes to it. Is it true? what does it absorbs?
    Last edited by a moderator: Oct 10, 2014
  2. jcsd
  3. Oct 10, 2014 #2


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    No mirror is 100% reflective, so yes, some amount of light will be absorbed no matter what. A perfectly reflective mirror would, by definition, reflect 100% of the light and absorb none. But these do not exist.
  4. Oct 10, 2014 #3
    Ok but what does it absorbs? does it absorbs all the color a little bit or something else happens
  5. Oct 10, 2014 #4


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    This doesn't quite make any sense, does it? If it is 100% reflective, then there is no absorption.

    What exactly are you asking here? Are you asking on what happened to the light that is not reflected in a typical mirror? Or are you asking for something else?

  6. Oct 10, 2014 #5


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    It will absorb a little bit of all the wavelengths. Mirrors can be made from many different materials to enhance their reflectivity of certain parts of the EM spectrum. For example, mirrors designed to reflect near-infrared light are typically made of gold because it reflects a larger portion of near IR light than most other kinds of mirrors. Aluminum is typically used to make visible light mirrors since it reflects a significant portion of visible light that falls on it, but will reflect less of other types of EM radiation such as UV or IR (it's also much cheaper than most alternative materials).

    See the graph below, which comes from here: http://en.wikipedia.org/wiki/Reflectivity


    As you can see, the amount of light reflected (measured by the Y-axis) changes depending on the wavelength and the type of mirror. Note that visible light has a wavelength between 400 nm to 700 nm. In this range the aluminum (Al) mirror reflects more light than the other two. Gold (Au) and silver (Ag) reflect more light in the near-IR range which is the right half of the graph.
  7. Oct 10, 2014 #6


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    Just FYI, posts from another thread have been merged into this one.
  8. Oct 10, 2014 #7


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    Aluminium also reflects different wavelengths more evenly, so the reflections appear in the same colors as the original.

    As seen from the side, mirrors often look greenish, revealing that they are not perfect mirrors but absorb different wavelengths a bit differently.
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