How well do you understand refraction? | Optics puzzles 4

Why bending, how can light go "faster" than light, and more
An equally valuable form of support is to simply share the videos.

Much of the last video, as well as this one, is based on the following Feynman Lecture:

Looking Glass Universe videos on the refractive index:

Timestamps:

0:00 - Why slowing implies bending
3:36 - Recap for how slowing happens
5:08 - Birefringence
6:19 - The barber pole
8:20 - When the refractive index is less than 1

Thanks to these viewers for their contributions to translations
French: LE PRAT Ronan, PyStL
Hebrew: Omer Tuchfeld
Portuguese: rose ✨
Russian: iverid

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These animations are largely made using a custom Python library, manim. See the FAQ comments here:

All code for specific videos is visible here:

The music is by Vincent Rubinetti.

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3blue1brown is a channel about animating math, in all senses of the word animate. If you're reading the bottom of a video description, I'm guessing you're more interested than the average viewer in lessons here. It would mean a lot to me if you chose to stay up to date on new ones, either by subscribing here on YouTube or otherwise following on whichever platform below you check most regularly.

testing an addition

[toxinlich]

I find this optics series great. Hope to see more physics videos from you in the future.

[kayturs]

This whole series just explained one of my greatest curiosities. I remember asking science teachers in high school who didn't care to give a detailed answer, and family and friends who didn't really think much about physics. I couldn't ask for a better visualization for something I've always wondered about. Thank you!!

[jounik]

Time to postpone the rest of today's plans by 13 minutes or so. That shouldn't be too much of a phase shift.

[al.]

Can we just appreciate how any type of Grant's series is more explanatory than the courses we have at literally our university education? We are blessed to have this free on internet.

[sammycorgi]

The fact that we have access to content like this for free is mad.

[stefanklass]

The 1st explanation of light bending and how to derive snells law is exactly how I was taught it in school. I had good science teachers

[JaredJeyaretnam]

The rotating pole is such a great analogy for why phase velocity can be greater than 1. I might have to steal that because it actually resembles a wave. (In fact, I’m saying now that if I ever end up teaching the appropriate course, I will 3D print exactly that model).

I’ve usually used the analogy of a laser pointer dot moving across the moon’s surface. If I flick my hand fast enough, I can make it move as fast as I like - even at speeds faster than c. But it’s an illusion too: the dot at one moment has nothing to do with the dot at an earlier moment, both came from my laser pointer on Earth.

[lopzag]

A quote that seems fitting: "Nowhere are the intimate connections between mathematics and physics more immediate then in optics" - Professor Michael Berry

[manuel_ao]

This video series that you have made is Gold and should be shown/taught in every optics lesson around the world.

[primenumberbuster]

Man please keep on with this Optics series. I want this series to reach Quantum level.

[PatricioHondagneuRoig]

I can't believe I totally understood this. You have a gift for explaining complex stuff 🎉

[Gork]

As an undergrad research assistant in an optics lab, this series is awesome.

Would love to see an explanation of evanescent fields if you’re continuing the optics stuff.

[barrypickford]

Making visually intuitive reps like this is what sets this Channel apart from others by light years.

[peterp-a-n]

Is this peak informational content? For real it doesn't get any better than this.
Stellar work!
I have goose bumps and teary eyes, I kid you not.

[joelklein]

3B1B is having his Physics arc😂

Great video! It's amazing how illustrative your explanations are even on science😊

[Luunnr]

The pure amount of things 3b1b taught me is genuinely impressive. Im in my early highschool years and you are the person that inspired me to learn math and math adjacent fields, Thank you so much.

[AlecHamilton]

9:44 is I feel the most critical point of all -- the light is NOT slowing down. I feel very strongly that this should have been mentioned almost first thing in the first video from a few days ago, because it was an unanswered curiosity in the forefront of my mind for that entire video. I think it's much, much more interesting to answer "why does light slow down in a medium?" with "it doesn't, actually -- it's actually a common misconception. But, it does APPEAR (in some ways) to slow down, because the very fact that it's interacting with electrons in the material generates a 2nd light wave, which intereferes with the original light wave. The result is a sum of 2 light waves as it travels through, a sum which gives the illusion of a slower wave, and here's how mathematically that works." Regardless, excellent videos. And if I am incorrect on some point here do let me know.

[poisionivy]

This series is amazing. I never guessed that the barber pole phenomena was because of different chiralities of the circular polarization of light! Thank you

[BlueRaja]

Another example I heard in school of something moving faster than the speed of light (without breaking causality): It takes about 1/80th of a second for light to travel from one end of the moon to the other. If you shine a laser light at the moon and flick your wrist, you could pretty easily make a laser dot travel across the surface of the moon faster than that.

[Ijaakcek]

Your all videos are absolute gems on youtube.
I was watching you for 6years and every time i watch whole video and in the end want to watch more.