• Question: why is glass transparent since its a solid?

    Asked by to Becky, Clara, Daniel, Simon, Thomas on 12 Mar 2014. This question was also asked by .
    • Photo: Clara Nellist

      Clara Nellist answered on 12 Mar 2014:

      Hi @amran.

      Solid things can be transparent if they let light through. Since light can pass through glass (which is great because it’s how glasses work) we can see through it. Visible light (the bit we can see) is actually just a part of the light spectrum, which includes radio waves and x-rays. Some solids don’t let the light we can see through, but they do let x-rays through. This is how we can take a picture of a broken bone, even though we can’t see through it.

    • Photo: Simon Albright

      Simon Albright answered on 12 Mar 2014:

      It’s not being solid that matters, it’s what it’s made up of.

      Everything around us is made of atoms, a small positive nucleus surrounded by orbiting electrons. When a photon (a particle of light) hits an atom it can give it’s energy to one of the electrons but only if it has the right amount of energy. One of the things we learn from quantum mechanics is that the electrons in an atom can only exist with certain precisely defined energies. If a photon doesn’t have enough energy to make an electron jump from one energy to the next available energy it will pass through.

      So the reason that glass is transparent to visible light is that the electrons cannot exist in energy states to which the light could excite them. The reason ultra-violet is blocked is because it can excite the atoms in the glass, the reason infra-red is blocked is that it excites the molecular bonds within the glass. Visible light just can’t quite acheive either.

    • Photo: Thomas Elias Cocolios

      Thomas Elias Cocolios answered on 12 Mar 2014:

      Being transparent is indeed a very cool property of matter. Or should I say some matter.

      Fun fact: I heard last week that liquid helium (which is at -271 degrees!) is so transparent, you actually cannot see that there is anything in there! It looks completely like air. (like walking right into a window that is simply too clean…) I found that amazing and I had to share it =).

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