3blue1brown
patreon
Any questions related to the index of refraction?
🕑 Added 2023-11-01 12:30:53 +0000 UTCI'm aiming to get a draft of the next video to you within the next week. It digs into the math behind why light slows down as it passes through certain media, like water or glass. In particular, it aims to give a solid intuition for why the amount it slows down depends on the color of the light, which when I was a student was just sort of handed down as a fact from on high. This, in turn, explains why prisms, water droplets in the air, and the barber pole demo all display a spectrum of colors, though, in each of those cases, there's a bit of an added twist to the story.
As I'm putting it together, I wanted to reach out and see if any of you had questions related to the topic or anything you've ever wondered about prisms and indices of refraction. I can't promise to include all in the video, but I'll try my best for the ones that fit well!
Comments
3blue1brown
Great question! In the main video, note how we ultimately explain dispersion due to the (ω_r^2 - ω_l^2) term in the denominator of our final expression, where ω_l is the (angular) frequency of the light, and ω_r is the resonant angular frequency for charges in the material. Note how this means dispersion will be greater when both frequencies are close since there's where small changes to ω_l cause bigger changes to the ultimate expression. I briefly mentioned at the end how it's important to also include a damping term in our differential equation, which ultimately explains how materials absorb the energy of incoming light. What I didn't mention is that this absorption is strongest when ω_r and ω_l are close. Intuitively, this should make some sense, because if the dynamics are such that without a damping term, the oscillator gets going with some huge amplitude, then when you throw in that damping, the corresponding high-velocity will give a lot of "friction", meaning more energy loss.
Christopher Moon
I am very interested in the refraction of em radiation and its limits for example, how do you calculate the RI of a gamma ray or that of a microwave? I know there are some optics formulas for this, but I haven't found a reference so far despite years of very casual-looking (not just my clothes!)
Peter Pearson
I believe I've been told that if a material is highly dispersive in some range of wavelengths, there must be a strongly absorbent band nearby. The explanation involved waving hands and mentioning the "Kramers-Kronig relation", but seemed a bit beyond my reach. Is the math involved too strenuous for this video?
Probably completely naive, but I have always wondered if, beyond red, orange, yellow, green and blue, there is purple light? By "purple", I mean purple in the sense that it activates not only the receptors in our eyes that are sensitive to blue light, but also those that are sensitive to red light. That just doesn't seem plausible.
I'd love to see a neat explanation for total internal reflection being '100% efficient', intuitively it doesn't work since normal mirrors aren't perfect but this does. I thought it was so neat when I initially learnt of it
