Why can you see through some glass, but other types are reflective?
In: Physics
How much a material reflects light really depends on a lot of stuff: angle, frequency, how apart are the atoms, and so on (you can guess that different glass use different materials). So, I’m going to explain how some light gets reflected in the first place. Because of how I want to explain it (by talking about atoms), I won’t get into the atomic difference of different types of glass and how they interact wth light.
First, you need to understand how glass is transparent. These ELI5 comments can explain better than me([1](https://www.reddit.com/r/explainlikeimfive/comments/l474j3/eli5_how_do_electromagnetic_waves_like_wifi/gknfdm6?utm_source=share&utm_medium=web2x&context=3), [2](https://www.reddit.com/r/explainlikeimfive/comments/l6o63n/eli5_what_makes_glass_transparent/)).
But, their explanation doesn’t explain 2 things, refraction and reflection. That’s because electrons do in fact interact in light, kinda. A better way to put it is that they respond to light. The light doesn’t *just* go through as they explain.
When a light that doesn’t have the exact energy level passes an electron, it causes the electron to vibrate. How? Well, light and electrons are both waves in the same field, the electromagnetic field. That means when one passes through, it causes the other to wave, or in the electron’s case, vibrate. This then causes the electron to emit its own light (the same reason as to why the electron vibrates).
The “new” light has the same frequency as the “original” (” ” because they both still exist), but it’s dimmer and slightly delayed. That means their peaks don’t line up, and since it’s dimmer, their height is different (but remember the same frequency). Now, when 2 light waves exist close to each other, they interfere, like [this](https://en.wikipedia.org/wiki/Wave_interference#/media/File:Interference_of_two_waves.svg).
Now, we were only taking about 1 electron, but imagine there are millions, billions of them all in random locations (like an actual piece of glass). Every electron responds in a different way, due to atomic spacing, response lag, resonance (electrons prefer some light over others), and so on. But, most of the wave cancels each other but in 2 directions; you get refraction and reflection.
Now from all of that you can see how the material and the type of light (frequency) affect how much light gets reflected. While every electron responds differently, depending on the material, one way of responding is more likely to happen than others.
I’m sorry this isn’t for 5-year-olds, but this is the most I can simplify without leaving out the details.
If you’re interested in how it can be explained by quantum mechanics, Richard Feynman’s book, “QED: The Strange Theory of Light and Matter”, if I remember correctly, explained it. I’m reading it again, and if you’re interested in the properties of light, I recommend it. There’s barely any math.
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