Science Questions

Why is glass transparent?

Sun, 11th Oct 2009

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Question

Neil Denom asked:

Why is glass transparent? Iíve heard that glass can be made from sand. How is this given that sand is not transparent, you canít see through it, but you can see through glass?

Answer

Well if you look very, very carefully at a single grain of sand, especially if youíve polished up the surfaces, it is actually transparent.  Iíve looked through lumps of sand, quartz- white sand, through microscopes.  As long as itís polished, you can see through it.  Sand is intrinsically transparent.  The reason why you canít see through it on a beach is because it is in lots of lumps.  If you ever looked at the world through a glass or a piece of glass, especially if itís curved, everything looks distorted behind it because when light hits it, it slows down, it bends, it goes around a corner it gets refracted, and the light kind of gets bounced off.  Now, if you're looking at something large, you can still make up a picture behind that.  But if youíve got thousands and thousands of very small glasses, the light would all get refracted off one.  It would get refracted offsome others, and all the pictures will get mixed up and mixed up and mixed up, until eventually they get overlaid over one another and it looks white.

Chris -   So it must be the same phenomenon as snow looking white, but the water itís made from Ė if you see it in fish tank, is transparent.

Dave -   Yeah and even in ice itís also transparent.

Helen -   And then youíve got sort of yellow sands, black sands, and the other impurities that are giving it that kind of tinge of a different colour path.

Dave -   Yeah, you get different rocks in it.  Black sands are normally from basalts which is intrinsically black and those just arenít transparent and yeah, a bit of patchy clays and all sorts of things in there.

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