How wiggling charges give rise to light | Optics puzzles 2

An equally valuable form of support is to simply share the videos.

Timestamps:
0:00 - Recap
0:44 - The radiation law
6:10 - Simulating the radiation law
11:11 - Why the diagonal stripes?
16:31 - Why does it twist?

Thanks to these viewers for their contributions to translations
Hebrew: Omer Tuchfeld
Indonesian: akhyarr

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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.

[oreopoj]

In all honesty, from someone who completed a 4 year undergrad degree in physics and subsequently went on to do a PhD on a topic that involved polarized light - this video does a fantastic job of explaining the phenomenon and clarified many difficult concepts that usually get lost in the mathematical details about light-matter interactions. Bravo I say! I think it’s the animations that this channel author produces which have a magical way of making traditional static textbook diagrams come to life.

[timgabby]

This should be nominated for a communication prize. A winning video. Bravo.

[matthewparker]

Nothing makes me happier than seeing part 2 uploaded less than half an hour after part 1.

[roncho]

I have no words to express my admiration for.your work. I have been styudying EM waves for more than 30 years and its th first time I know somebody that can show 3D/EM waves in with this level.of detail in such a clear way. This animations should be what a genius like Maxwell could imagine more than 100 years ago. Its hard to classify you as a simple professor, because all this stuff requiere a high level of artistic sense too...you are like modern matematician artist as Leonardo Davinci was 500 years ago.

[bluebrown]

A few commenters have asked whether you'd see different angles for the diagonal stripes as you change the distance from the tube, as this explanation would imply. It's a good question! We actually did those measurements, where our expectation was for the diagonal angles to become more vertical as the camera moves away from the tube (i.e. there should be less variation in color as you scan your eyes from the top to the bottom). But, that's not what you see! If anything, the boundaries become more horizontal, in direct contradiction to what you'd predict from this explanation.

The tentative plan is to talk more about this in the following video because there's a nuance here that's actually related to indices of refraction. I believe what's going on here is that we need to incorporate the lensing effect of the tube. Even when you're standing far away, and the line of sight to the top of the tube is nearly parallel to the line of sight to the bottom, because of how those lines of sight will bend as they pass through the circular boundary of the glass and water, and they will no longer be nearly parallel as they enter the water itself.

So in effect, the explanation offered in this video is qualitatively correct, but to make quantitative predictions you need to add more detail.

[Danyel]

For those interested in a textbook that explains all of this and more, the best one I know is "Absorption and Scattering of Light by Small Particles" by Bohren and Huffman. It goes in detail for example in the difference between circular vs linear birefringence and dichroism. Also it was the first source that thought me about the Ewald-Oseen theorem---that's the secret sauce to understand what the index of refraction really is.

[iankrasnow]

In organic chemistry, we learned that you can measure how much the polarized light "rotates" to determine the ratio of left handed to right handed chiral molecules in a racemic mixture. What's surprising, and beautiful, is that this effect is visible on such a length scale. Each full twist is a significant fraction of a meter in length, rather than being microns in length, so it's actually visible and really easy to see!

[Infinitum-]

Frankly, there is not a single channel on this entire platform, that is a of a higher quality. Concise, rigorous, profound; broad and foundational. So most importantly: beautiful! Grant, you are a treasure.

[allanjmcpherson]

Fun fact: The charge wiggling in the z-direction is called dipole radiation, and it's what antennas use. The drop to zero in the z-direction is why you actually get very poor cell reception when you're directly under a cell tower.

[calinacho]

Take a shot every time he says "polarised"

[DrDeuteron]

FYI: this effect is used in GPS. The ionosphere rotates the polarization of the L-band signal (Faraday rotation). By transmitting circular polarized radio at 2 frequencies, L1 and L2, the difference in the delay can be used to find the total delay, and since GPS is based on timing, you need to know the travel time btw satellite and receiver.

[MinecraftLiqid]

I am an undergrad math-physics student that will go on to teach others. Having worked in Manim a bit I cannot fathom the amount of time/skill you had to employ in making this short video. Yet you have already surpassed most of my phisics teachers and I can finally see, that it is indeed possible to learn and teach these things without all the pain I had to endure. This is so much different from the explanations I had been given that I wouldn't even believe it was possible with this much elegance and apparent simplicity of this problem. I can only dream and pray that I will achieve this level of expertise in explaining concepts. You are really the best role model I could dream of and since I hope to be using Manim while teaching as well, I can only thank you for your huge effort you already did for us. You helped me see math and physics with the kind of passion and beauty I saw it before the hardships of university came. I hope this motivation will help me with my studies and that I will have the opportunity to pass this feeling onto my students in the future. You really are among the most brilliant minds in modern times, at least in the field of pedagogy. Hats off to you.

[James]

This is what finally made the concept of "light is a wave" click for me. No amount of time in my physics class would have done that. So cool!

[bimblinghill]

Something in my brain went click. Having experienced years of education, dozens of books, hundreds of videos in this general area, this video makes several fundamentals I've never understood just jump out. An outstanding piece of educational work. Thank you!

[bolognious]

The visualizations of the fields youve created are honestly astounding. I am a post-masters student with a specialty in Quantum Optics and it was just so nice to see this visualized this way. Sometimes the visual connection really just helps it all make more sense.

[catcatcatcatcatcatcatcatcatca]

I almost feel tricked as you offered a very intuitive model and explanation for electromagnetic field and maxwell equations, as well as light polarisation.

Through deception you fooled me into developing some intuition of induction.

[Biga]

Wow. This, and the part 1, are just mesmerizing to watch. Very well put together and just beautiful with the combination of the footage from the setup and the animations. Some of the best editing I have seen and the cadence of the presentation matches so well with it and delivers the information at a very natural pace.

I especially appreciate the little caveats that you give. They really help to keep people on track.

[juanamenabar]

As an Artist an Math/Science Lover (I`ve watched all af your videos), This touches me deeply, I can only be grateful through a youtube comment, but really and truly, your work has influenced me deeply for years, at some part of the video I clapped out of joy!
Yours truly.
- Juan (Amenaza) Amenabar

[logician]

We all just got linearly polarized in order to get to this video

[mayflowerlash]

Grant, this is simply brilliant. Imagining how the electric field from a charge (a moving charge) acts on another charge is damn near impossible. The mind of a cave man did not evolve to deal with the task. Yet you have shown you are capable. That is mind blowing.
Do you intent to make an animation showing how the magnetic field oscillates as light is propagated?
Thank you for enlightening we mere mortals with such a brilliant and clear explanation.