Polarized light in sugar water | Optics puzzles 1 

Can't wait for the final video! As always, your animations add so much clarity.

Fun fact: Measuring the angle between the two filters can provide an estimation of the amount of sugar in the solution. This trick is applied to precisely evaluate the amount of sugar in wine grapes and must. These animations are awesome!

Hey folks, Quinn here. Lots of people have been asking how they can make this demo themselves, so here’s how I built it: Materials: ⁃ Table sugar (sucrose) ⁃ Water ⁃ A glass tube that you can fill and seal, although it would be cool to experiment with different materials for the tube, since different material = different index of refraction. More on this in part 3 of the video. The tube should be long enough so that you can actually see the effect from the sides - our tube is 1 meter long, but you’d probably be able to see the effect with a ~0.5m tube. You also might want to make sure the tube is easy to open so you can clean it. See “Things to consider” for more. For the mini-demo, I just used a drinking glass! [FYI, the tube in this demo was custom-made for the MIT Physics Department. I’m not sure exactly where it came from or what type of glass it is exactly…] ⁃ A source of white, unpolarized light. We used a Dedo lamp, and if you make the demo as big as we did, you need a pretty powerful light source. For the mini-demo, I used my phone’s flashlight! ⁃ Two linear polarizing filters. You can get ‘em online pretty easily! Directions: ⁃ For our demo, we made a sugar solution of 300g of sugar per 400g of water. So, you should measure the volume of your tube and scale this ratio accordingly. ⁃ Boil the water and mix in the sugar until it’s dissolved. ⁃ Let the solution cool, then fill the tube with solution. Close up the tube. ⁃ Place the light source so it’s shining down the length of the tube, then place a filter between the light and the tube. ⁃ Place the other filter at the end of the tube. ⁃ Voila! You can rotate the first filter to see the whole spiral move up and down the tube, or you can rotate the last filter to see the color coming out of the end of the tube (and through the last filter) change. Things to consider: ⁃ You really want the tube to be clean before you start, since the solution can get moldy. If you look up close, you’ll actually see little floating things in the solution - those are some bacterial friends :) ⁃ We try to replace the sugar solution frequently so that the demo is clearer. ⁃ The shorter the tube is, the more concentrated you want the sugar solution to be in order to see a similar effect. ⁃ The amount of rotation of the polarization angle is proportional to the concentration of the solution (this is called the specific rotation!) ⁃ The light might get hot the longer you keep it on, so be careful! As always, observe sensible safety procedures. ⁃ You could do this with different sugars! Glucose would also rotate light to the right, but slightly less than sucrose. Fructose rotates light to the left! If you recreate this/do something else cool with it, I’d love to see!

Love to see Grant branching out. He's truly made an impact on all online education, not just math! ❤

I've studied light/matter interactions for 20 years, published papers and such, and had never seen this before. I was pleasantly surprised! I wouldn't have thought you'd see light via the side. How great The more you learn the more you realize you know next to NOTHING

What a beautiful demo setup!

I'm an optical engineer. I have solid intuitions about light. I still said "what?!" out-loud involuntarily when the lights dropped the first time. What an amazing video!

A landmark in science communication. Thank you and congratulations.

This is like being at the center of the research table of grant, listening to the ideas and just absolutely loving your time learning. This is exactly what college/higher education needs to be, collaborative on a world level. Ofcourse, i am only a viewer and not a collaborator, but it just feels insanely amazing to be able to listen to this information

I first saw this in 1973, in Walter Lewin's class on vibrations & waves at MIT. Damn, he was a great lecturer.

Part 2 is available now: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-aXRTczANuIs.htmlsi=m6DgY1ogMrwTRrUP Some viewers have asked about how to make this demo for themselves, and Quinn kindly wrote up the description below. Materials: ⁃ Table sugar (sucrose) ⁃ Water ⁃ A glass tube that you can fill and seal, although it would be cool to experiment with different materials for the tube, since different material = different index of refraction. More on this in part 3 of the video. The tube should be long enough so that you can actually see the effect from the sides - our tube is 1 meter long, but you’d probably be able to see the effect with a ~0.5m tube. You also might want to make sure the tube is easy to open so you can clean it. See “Things to consider” for more. For the mini-demo, I just used a drinking glass! [FYI, the tube in this demo was custom-made for the MIT Physics Department. I’m not sure exactly where it came from or what type of glass it is exactly…] ⁃ A source of white, unpolarized light. We used a Dedo lamp, and if you make the demo as big as we did, you need a pretty powerful light source. For the mini-demo, I used my phone’s flashlight! ⁃ Two linear polarizing filters. You can get ‘em online pretty easily! Directions: ⁃ For our demo, we made a sugar solution of 300g of sugar per 400g of water. So, you should measure the volume of your tube and scale this ratio accordingly. ⁃ Boil the water and mix in the sugar until it’s dissolved. ⁃ Let the solution cool, then fill the tube with solution. Close up the tube. ⁃ Place the light source so it’s shining down the length of the tube, then place a filter between the light and the tube. ⁃ Place the other filter at the end of the tube. ⁃ Voila! You can rotate the first filter to see the whole spiral move up and down the tube, or you can rotate the last filter to see the color coming out of the end of the tube change. Things to consider: ⁃ You really want the tube to be clean before you start, since the solution can get moldy. If you look up close, you’ll actually see little floating things in the solution - those are some bacterial friends :) ⁃ We try to replace the sugar solution frequently so that the demo is clearer. ⁃ The shorter the tube is, the more concentrated you want the sugar solution to be in order to see a similar effect. ⁃ The amount of rotation of the polarization angle is proportional to the concentration of the solution (this is called the specific rotation!) ⁃ The light might get hot the longer you keep it on, so be careful! As always, observe sensible safety procedures. ⁃ You could do this with different sugars! Glucose would also rotate light to the right, but slightly less than sucrose. Fructose rotates light to the left!

The visualisations is on another level. I am incredibly impressed by how you can create these moving 3D animations to show super complicated concepts.

Im a chemist. the dependence of angle of polarization by a chiral molecule on frequency of light is a very useful phenomenon which gives rise to cotton effect. Different molecules and even parts of a molecule have a different signature and thus the plot of angular dispersion vs. freq can help identify a molecule and functional or structural motifs. See Circular Dichorism spectroscopy

every video of this guy is a phd paper

I remember learning about chirality in Chemistry 201. Most of the time I'm mostly along for the ride, but today it did feel intuitive. Learning from you has completely changed my view of mathematics, and I thank you for that.

Steve Mould and Grant Sanderson has the best therapy voice of all time. ;)

I came to this video as someone who only vaguely remembers some HS optical physics so I didn't expect to be too intrigued. Instead, that animation and explanation moved mo to the verge of tears. So beautiful and curiosity-enabling

3blue1brown never disappoints. The videos are always of high quality, it's borderline rare, Plus this guy is a great source of inspiration, just that, well done. Hello from a guy in France.

This is such a great video with the way it's setting up other discussions. Thank you for making physics accessible!!!

My jaw dropped when the spiral rainbow appeared. So freakin cool!

Having played around with a lot of polarizing filters and looked through a ton of information about how it works with scattering, I have built up an intuition, and I am really excited to see how you make it easier to understand.

You have such a gift at explaining complicated subjects in interesting and engaging ways. Thanks for another excellent video!

A day with a 3blue1brown video is always great but a day with 2 uploads is exceptional!

As always, your visualizations are beautiful in their elegance and simplicity, and really help to explain the concepts. Well done.

I saw this video as one of the great documents some immense scientist from the 19th century left as his legacy. What youre doing is just incredible, a friend of mine and I literally chose our graduation courses (Mathematics for him, Mech. Eng. for me), greatly thanks to your influence during our high school. Thank you for your ridiculously amazing work!

Grant is trying something new, adding a bit of physics experiments to the recipe! Glad to see that the channel is looking towards a bit of variety. Not that the usual maths animations were bad, they were exceptional as ever, but this is great to exploit the viz towards more intertwined maths and physics, I love it. Keep it up, Grant!

What a fabulous demo. I would have loved to see this kind of display when I was taking college physics. The coordination between the rotation angle of the polarization, the brightness of the output color, all coordinated. Brilliant. This reminded me strongly of Feyneman's book, QED. Thanks Grant!

This is the first physics video I have seen from this channel.

I have never seen this phenomenon before, which is a surprise because I love Steve’s videos. What a beautiful phenomenon that’s quite easy to replicate! Seeing this in science class as a kid would have seemed like magic.

3b1b physics videos are a delight to see

the visualizations add so much depth to the explanations, actually awesome stuff.

These animations and narration are sublime.

Thanks for lighting me to this new knowledge.

This is a phenomenon occurring due to optical activity of sugar. Known as optical isomerism. If a compound is optically active , it will bend light to a certain degree. I don’t know why this wasn’t mentioned in the video.

Incredible collaboration, another video gem packed with knowledge and clean understandable explanation, thank you!

This is such a lovely video. The explanation, the slow build-up to the problem expressed at the beginning, and the music... sooo good

Oh nice, glad to see a new 3B1B video!

I am a British Physics teacher working in China. I really appreciate the questions you ask and how you ask them/ explore ways of answering. gets to the core of what we are trying to encourage in our students. Great work

Great video, Grant! This is a really interesting topic. I loved Steve Mould's introduction of this phenomenon. Quinn Brodsky did a fantastic job with that setup! I love the mesh of the visceral demo and your animations. I can't wait to watch all of your videos on this!

I insist. This guy deserves the Nobel Prize in Education. And given that it doesn't exist, he also deserves it to be created.

Wow! I’ve loved your videos for quite some time, @3blue1brown, but I’ve never felt so excited as just now seeing this teaser. I did a PhD and postdoc in optics 20 years ago, in areas very close what you’ve shown here. This is the clearest and most beautiful video I’ve seen on this topic and I am already learning something I didn’t know before. Thank you so much for everything that you for maths and physics education around the globe!

Very nice topic! When Math meets Physics, things get interesting :)

This is better than Christmas...I love these very tangible, available examples of the complexity in the world and how it leads to fascinating experiences.

You have a gift and I am so grateful to watch this without paying you any money.

I am very much using this video in my classes, and my heart jumped a little when I saw you could do the demo yourself! We are adding optics back into our curriculum (highschool physics) and this will be so interesting to see

Subtitle nitpick at 6:04: s/weekly/weakly/ Very much looking forward to the next video 👍

The way you mentioned the answers without explicitly stating the methods really jogged my brain in an exciting way. Being able to think about twisting polarized light and angles of refraction together really gave me an AHA moment that saying "polarized light twisted at a sufficient angle from a surface would experience total internal reflection" just wouldn't have provided

This concept is pretty simple and just another beautiful display of the properties of the universe unfolding through our ideas for setups.

My feeling for question 3 could be due to the tube acting like a prism, scattering different light at slightly different directions, magnified by the lens effect of the cylindrical tube.

Holy mother of god this is great! Optics was one of my weakest subjects in physics. It felt like a lot of it was just "this is how it is." I'm so excited to follow this series. I feel embarrassed, though, that as someone with a degree in chemistry that I didn't even consider the chirality of the sugar. I've used polarimeters in lab! Duh!

I did a presentation on this last term form my final physics project. There was not a whole lot of information online so it was very fun to figure out! Great job explaining it. I also didn’t think to look at the side of the tube when preforming the experiment.

Very intriguing! Eager to watch the next video.

As a polarimetrist-- this is so great! I'm so exited for these videos. You and Steve Mould are my favourite STEM communicators (and not just because you have both covered polarization multiple times). So exited for this series (And thanks to Quinn for coming up with this!)

I can’t find my old correction so I am reposting it here: Hey there, I have a fundamental correction to the visuals in this video. The polarizing filters are oriented incorrectly. When the polarizer is vertical, it will transmit horizontal and reflect vertical. It’s a common misconception, if you would like to hear more I would be happy to share! (I am an electrical engineer with a passion for light haha) PS these are some amazing quality videos! Edit 1 for clarification: An experiment I performed in undergrad involved a square with equally spaced vertical wires. We placed it between a transmitter and receiver (transmitting vertically polarized EM waves, maybe 3GHz but I don’t recall). When the wires aligned with the direction of polarization, the receiver signal dropped drastically and vice versa.

This video is amazing. I love your videos in general, but this is the most amazingest you've done, imo.

Best video of yours I've ever watched. Fantastic

Yahhhh! Don't always like a cliffhanger but in this case, it means more 3B1B videos. Can't wait!

Didnt expect to see Blue's upload right on the start of September, cant wait to see another next month or in 2 months..

I love this gathering of a couple of my very favorite RU-vidrs.

Quantum physics lets go

QUINN BRODSKY DESERVES MAJOR PROPS! *What* an idea and solid execution of said demo! We likely wouldn't have had this video *without* her perspective. Thank you for returning to this in *force* 3B1B! And including Steve Mould was just icing on the cake~ 💎

These visualizations are absolutely top notch!

beautiful and fascinating ; well done ; looking forward to the rest of this indeed

I was guessing that the curvature of the pipe has something to do with the diagonal stripes. I was wondering if it would look different in a square tube. Looking forward to understanding the rest of this video series so I can make a hypothesis about what a square tube full of syrup would look like

Great content. Keep up the insane work 😊

Beautiful experiment. As someone who worked in spectroscopy with chiral molecules, I must say this is a must demonstration in graduate classrooms. The experiment has refravtive index, polarisations, optical rotation due to chiral molecules, all playing their role simultaneously.

Impressive experiment! So simple and so deep in knowledge! Mind blowing! Congratulations for the videos!

1:48 Ok, now I want a floor lamp filled with sugar water with a slowly rotating polarizing filter. Also I wonder what this would look like if you mirrored the far end so none of the light escapes out the top - would the light twist back to the original orientation and cancel out the apparent spiral of colors?

classic 1000% likes to views ratio right now

Really cool phenomena and an amazing delivery as usual! As a physicst I really like it

Watching this and I was just waiting to chip in about the Steve Mould video and, of course, you not only know of it, or give it a shout out, but you speak to the man himself. Really nice work, as always!

First

Finally a 3b1b video where I have an intuition for. Love your math vids and love to see your take here on my topic from physics.

That's pretty cool. took me just past half way, I paused for some seconds and the rest of it was confirmations but explained so much better than I could.

This is the best RU-vid video I've seen in years. You REALLY nailed this

I love this channel more than anything.

Love this channel. Thank you so much!

Man, you deserve a Nobel just fot those animations!

JUST AMAZING!! Congrats and thanks for this video!! I have some time wanting to create this experiment

Yes! I waited so long for this exact explanation of light

I love how attentive and interested the cat is that's watching the home experiment at 6:45 😻

Your videos are always brilliant. These are the instructional videos that would make physics (and maths) classes so much more understandable without mental visualisation gymnastics.

love these visuals they makin me fr interested

Thanks it's amazing to see a live full visible light spectrum . A landmark in science communication. Thank you and congratulations..

Neat video, can't wait for more of the series!

This was impressively well done. Thank you for a great lesson in light

Educational youtube is so enriching. I'm so grateful for this content.

such a joy that this dropped when i am studying about optical activity in my chemistry lectures.

Guy is such a good story teller

i like your way of explaining things so much

Thank you, fantastic video. This is really useful in the work I am doing on coloured light and primary colours.

how you ambushed him with the question was perfect👌🏽

This was a great video, can't wait for part 2.

Awesome! I didn't know you make physics videos. This is as good as your math videos! Keep up the great work!

Like the twist in dna or a gyroscope tracing the turn of the planet axis. Beautiful.

Great idea for a video series! Psyched to see it all!

was just thinking about Steve's original video this last week, and wondering about different methods of tuning the output color. perfect timing

Very impressive presentation. Thank you.

So humble. Grant refers to the beautifully illustrated and insightful animations as mere cartoons

This is a great teaser for my 3rd semester of physics, where we cover optics. Perfect timing 3B1B, thanks alot!