Why some medium are transparent?
Some medium, or media, plural, are classified as transparent because they allow all wavelengths of visible light to pass through them. Not only do they allow the light to pass through them, they do not diffract, or bend the waves in any manner. No distortion or fuzziness occurs as does in translucent media, which allow the same wavelengths to pass, but have enough substance in their material to cause the bending and deflection of some of the waves. A good example of a medium that is transparent is plastic sandwich wrap, commonly called Saran-wrap. Sandwiches wrapped in this material are easily identified because you can see right through them. An example of a translucent medium would be wax paper, which you can still see through, but not as well. It is harder to tell what type of sandwich is wrapped with wax paper. Then you have the opaque medium, which does not allow light to pass through it in any form whatsoever. Aluminum foil is a great example of opaque media; sandwiches wrapped in this material are a "guessing game", because you can't see through aluminum foil at all.