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What objects block sunlight?


amg
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For homework, I have to decide whether some objects or conditions block sunlight and their Ultraviolet rays completely, mostly, somewhat, rarely or not at all.

 

I was given these following conditions:

 

Water (not a bunch of water, like 1 cm deep or dripping leftover water

Clothing (White Cotton Undershirt Sleeveless)

Eye Glasses (The one people wear on their faces to see better)

Window Glass

Sun Glasses

Sunscreen SPF 30

Copy Paper

Ziploc Plastic Bag

 

I'm guessing:

 

Water - It shouldn't block any UV rays

Clothing - It would probably block most UV rays

Eye Glasses - Maybe some rays, like 30-40%

Window Glass - It should block most UV rays but not all, like 80-90%

SunGlasses - It should block all UV rays

Sunscreen SPF 30 - It should block all UV rays

Copy Paper - It should block most, like around 70%-80%

Ziploc Plastic Bag - Maybe around 20-30%

 

 

Can someone tell me whether my guesses are correct or incorrect and if they are incorrect, it explain why. I tried to base most of my guesses from how transparent they are, but I am not sure if that is completely related to sunlight.

 

Edit: Or, I am looking at this incorrectly, maybe this is just a yes or no question on whether certain objects block UV rays or not, but I am not sure.

Edited by amg
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Water (not a bunch of water, like 1 cm deep or dripping leftover water

Clothing (White Cotton Undershirt Sleeveless)

Eye Glasses (The one people wear on their faces to see better)

Window Glass

Sun Glasses

Sunscreen SPF 30

Copy Paper

Ziploc Plastic Bag

 

Sunscreen(might depending on the brand)

Eye Glasses(No, but they do have new UV protection kind) In Sunglasses to

(Glasses often glare with sun and sometimes glass just amplify sun(If you cant stop the sun I doubt you are going to stop the UV rays)

Sun glasses(Its been proven shown normal sunglasses dont always protect against UV so they made special UV sun glasses)

 

They made a lot of new UV protection stuff in recent years since they did not protect against UV.

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It's very difficult to answer this question because the answer depends rather strongly on a few other things

What is UV?

and exactly what are the things made of.

Pure water doesn't absorb much of the UV that reaches us from the sun. Sea water or muddy water will.

 

My glasses are very good at blocking UV. It correlates fairly strongly with having a high refractive index. But a cheap pair with actual glass (rather than plastic) might hardly block UV at all.

 

If the sunscreen actually has a SPF of 30 (and the question says it does) then it lets through nominally 1/30 of the UV and blocks the other 29/30 so it blocks something like 97% of the UV.

 

Window glass- who knows?

It probably blocks a lot of the shorter wavelength UV but relatively little of the longer wavelength stuff.

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