Why is glass transparent?
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a quick, intuitive explanation of transparency and energy gaps, often as the starting point for follow-up questions about absorption, x-rays and reflection.
Recommended by 2 people across 2 different months, 2012 to 2025.
What it is
A short Sixty Symbols video in which Professor Phil Moriarty explains why glass is transparent, using the idea of an energy (band) gap that visible-light photons cannot bridge. The description includes a correction: the final sentence was misspoken, and the point is that photons lack the energy to excite electrons across the gap, so light passes through.
What people said
Recommends Alfavoufsila · 2012-10 · Physics Stack Exchange · on “What is primary reason for a matter to be transparent as Cornea is?”
I found out inspiring teaching on transparency of glass and why it is transparent for some frequencies( light). -http: [this video]
Recommends Michal · 2014-05 · Physics Stack Exchange · on “Why doesn't more light bounce off of things in the manner of sound?”
This happens because sound wave Defract [LINK] (bend around corners), this only happen when the wavelength is roughly comparable in size to the gap in question. Human hearable (20Hz to 20kHz) sound waves have a wavelength on the order of a couple cm to 2 meters, which is similar to commonly encountered gaps such as a door cracked open. Heres a calculator [LINK] to find it exactly. On the other hand visible light waves have a wavelength on the order of a couple hundred nanometers - too small to diffract in a doorway. However radio wave (also electromagnetic radiation - just like visible light) have larger wavelengths and can diffract around such obstacles Another point involves sound passing
Cites Neon22 · 2012-12 · Physics Stack Exchange · on “Transparency of solids using bandgaps and relation to conduction and valence bands”
I think I understand how a solid can appear transparent as long as the energy of the photons travelling through it are not absorbed in the material's bandgap. But how does this band gap relate to conduction and valence bands which explain insulators, semconductors, and conductors as described in the 'band theory for solids' (say) here: [LINK] ? Specifically I wish to use answers to this question to construct a useful visualisation of this aspect - trying to explain to lay people why some solids are transparent and some are semiconductors (or both) and using the bandgap to do so. See a basic, perhaps rushed, explanation of transparency started here: [this video] There are two good reference questi
Cites Goncalo Fonseca · 2018-03 · Physics Stack Exchange · on “Energy Levels: Reflection or Absorption and Emission / Color of Objects and Emission Spectrum”
This is a question that involves different topics that are related to each-other and I think it´s faster more enlightening to put everything in one question than to have multiple questions. First of all, one of the first things that I learned on this subject was that the color of an object is the result of the reflection of one color/wavelength and the absorption of all the other colors/wavelengths in the visible light spectrum . Until here everything is fine and simple, and now I move on to learn about light reflection, and I learn that light on a flat surface reflects light at the same angle of the incident light. After that I started to learn about the energy levels of elements and how el
Cites Oleg Riabov · 2022-12 · Physics Stack Exchange · on “How does photons bounce back after being absorded by the atoms?”
I just watched a video from the channel "Sixty Symbols" called "Why is glass transparent?". Link: [this video] The explanation about why some materials absorb light and some don't was something like this: "When a photon passes through an electron, it elevates the energy level of this electron from the ground level to the upper level and because of that the electron is being absorbed, but in glass this energy gap is too large, so the photon just passes through the atoms." So, do I understand correctly, that if the photon hit the wall it has to be absorbed. If all the photons are being absorbed by the wall, then how do they bounce back into my eye? As far as I know objects reflect the light that th
Cites ranieri · 2025-02 · Physics Stack Exchange · on “Why doesn't the energy gap prevent x-ray radiation through mediums?”
Just watched this [this video] video titled 'Why is glass transparent?' The professor basically sums it up as, "All materials have an energy gap, bricks have a lower energy gap than glass so electrons will absorb visible light in bricks but not in glass". This logic is really intuitive but I wondered, since x-ray radiation has higher energy levels than visible light, shouldn't it be more prone to be absorbed by materials. How come x-rays are used exactly to look through materials that don't let light through, then? There must be a logical caveat I'm missing.