[Waves] Wavelength and surfaces penetration

In summary, Bobby doesn't believe that sunglasses are necessary to protect against UV radiation. He recommends that people learn more about the dangers of UV radiation and seek quality protection.
  • #1
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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
 
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  • #2
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.
 
  • #3
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
 
  • #4
Drakkith said:
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.

Yeh, I imagined that material would have a role in this problem. Thank you for your answer!
.
Bobbywhy said:
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

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!
 
  • #5
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).
 
  • #6
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.
 

1. What is the relationship between wavelength and surface penetration?

The shorter the wavelength of a wave, the easier it is for it to penetrate through a surface. This is because shorter wavelengths have higher frequencies and higher energy, allowing them to pass through obstacles more easily.

2. How does the angle of incidence affect the penetration of waves?

The angle of incidence refers to the angle at which a wave hits a surface. The more perpendicular the angle of incidence, the easier it is for the wave to penetrate through the surface. This is because a perpendicular angle allows the wave to travel directly through the surface, rather than at an angle.

3. Can the material of a surface affect the penetration of waves?

Yes, the material of a surface can greatly affect the penetration of waves. For example, materials that are denser, such as metals, are more difficult for waves to penetrate through compared to materials that are less dense, such as air or water.

4. What is the difference between surface waves and bulk waves in terms of penetration?

Surface waves, also known as Rayleigh waves, travel along the surface of a material and have a circular motion. They have a lower penetration depth compared to bulk waves, which travel through the interior of a material and have a back-and-forth motion. Bulk waves have a higher penetration depth and can travel through thicker materials.

5. How does the frequency of a wave affect its penetration through a surface?

The higher the frequency of a wave, the easier it is for it to penetrate through a surface. This is because higher frequency waves have shorter wavelengths, allowing them to pass through obstacles more easily. However, very high frequency waves can also be absorbed by certain materials, limiting their penetration depth.

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