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[Waves] Wavelength and surfaces penetration

  1. Sep 21, 2013 #1
    Hi everybody!

    Just 2 important notes: I don't study physics and so I'm not sure if this question belongs here (but I don't know where should I put it..); second I'm not english native, so ask me if I did not explain somthing enough.

    My electronic professor told once in my class, that you don't have to buy expensive sunglasses to be protected from UV rays. He said that UV rays have a wavelength under 400nm and therefore they can't penetrate in objects with higher thickness. Unfortunately I wasn't able to find anything online about wavelength and penetration capability.
    Was him right? If so could you explain me how this thing works?

    Thank you so much, bye
     
  2. jcsd
  3. Sep 21, 2013 #2

    Drakkith

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    Staff: Mentor

    Not exactly true. Visible light has a wavelength of about 400-650 nm yet it still penetrates glass many inches thick. Some materials are transparent to UV light. I don't know the details well enough to say anymore than that, sorry.
     
  4. Sep 21, 2013 #3

    Bobbywhy

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    Gold Member

    Ultraviolet (UV) radiation can damage human eyes permanently. Do NOT take any risks with your eyes...you cannot undo the damage the UV radiation causes.

    Learn about the subject, be sure you understand it, and always use certified, known quality protection for your eyes. Here are 3 websites to start you off on your learning process:

    1. “UV Protection
    Ultraviolet (UV) rays from the sun can damage your eyes by contributing to cataracts, macular degeneration and growths on the eye, including cancer. All of the sunglasses offered at REI block 100% of UV light.
    • UVB rays are the main concern for eyes. According to the American Academy of Ophthalmology, "Long-term exposure to ultraviolet (UV) radiation in sunlight is linked to eye disease. UVB radiation is considered more dangerous to eyes and skin than UVA radiation."
    • UVA rays are the primary ones absorbed by your eyes. While they pose far less concern than UVB, doctors still recommend that they be avoided.
    • UVC rays are not a concern, as they are blocked by the atmosphere.
    UV protection information should be printed on the hangtag or price sticker of any sunglasses you buy, no matter where you buy them. If it isn't, find a different pair. Also keep in mind that cheap, tinted sunglasses with limited UV protection can actually do more harm than good, as they cause your eye lenses to open up wider, leaving them even more vulnerable to UV rays. Kids' eyes are especially vulnerable to UV light, since they don't have the same level of natural protection as adults.”
    http://www.rei.com/learn/expert-advice/sunglasses.html

    2. http://www.mayoclinic.com/health/uv-protection/AN00832

    3. http://www.glaucoma.org/treatment/a-guide-to-sunglasses.php
     
  5. Sep 21, 2013 #4
    Yeh, I imagined that material would have a role in this problem. Thank you for your answer!
    .
    Thanks to you too Bobby, safty before everything and I would not exchange my rayban for anything. But the post itself is about UV under a physics point of view, the sunglasses story is just a 'background' to point out my doubts.

    For future answers, please stay int the physics area!
     
  6. Sep 21, 2013 #5

    BruceW

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    Homework Helper

    the physics answer is what Drakkith said. it depends on the material. Probably the simplest model for attenuation of EM wave is an exponential decay law http://en.wikipedia.org/wiki/Penetration_depth So the wave never dies off fully, but you could calculate the distance at which the wave has 1% its original intensity (for example).
     
  7. Sep 21, 2013 #6

    Claude Bile

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    Science Advisor

    As a rule of thumb, most silicate glasses have a wavelength transmission cut-off around 320-340 nm.

    It is well documented though that UV radiation greater than 340 nm still has adverse effects, and so ideally you should ensure that your UV protection extends into the visible.

    Claude.
     
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